When I worked the KH1 DXpedition on several bands earlier this year I briefly celebrated. According to my records it was DXCC country #300 worked since I returned to the air in 2013. As it turned out my records contained a few errors. Baker Island was #299. Eventually #300 came along with Ducie Island VP6D, a DXpedition that is ongoing as I write this. Of these 280 are confirmed via LoTW, which is the only way I QSL nowadays.
It is a milestone that was achieved more slowly than I expected. Consider that I reached 225 countries in two years using a maximum of 10 watts and modest antennas. Spotting networks and information dissemination about activity in rare locales makes running up the country count easier than ever.
Amusingly, the first 100 countries were easy enough despite running QRP and recruiting the
aluminum eaves of my house in Ottawa as a random wire antenna. That was great fun. Doing it that way -- with a tiny station and low expectations -- played an important role in rekindling my passion for the hobby.
With DXCC the law of diminishing returns applies: as the country count increases each incremental country requires more work than the last. By the time 300 countries are reached the required effort is quite high and the progress slow.
My lifetime total is perhaps 315 or 320, reduced by deleted countries during the years I was inactive. But that number doesn't interest me. I wanted a fresh start after a 20 year hiatus from the hobby as a way to measure my progress. DXCC doesn't mean much to me and I have never applied for the award. I likely never will. It is the activity of DXing that I find appealing.
Maybe it's the excitement, maybe it's the competition and maybe it's the simply the magic of radio. Perhaps it's explained by catching the DXing bug when I was young, decades ago, when global communication was a rarity, except for those who got into ham radio. Youthful passions tend to linger.
Rather than dwell on the 300 country milestone what I'd like to do in this article is discuss the ones I have yet to work. With 340 countries on the current DXCC list that there are 40 countries left. By the end of this article it should be evident why working them all, or achieving the lesser but still heady level of DXCC Honour Roll, is so incredibly difficult. Most DXers who have done it have taken a lifetime to get there.
I'll group countries together where it makes sense to do so to keep this article from becoming repetitive and too long. Apart from the grouping, countries will be ordered by prefix.
3D2C Conway: I vaguely recall some DXpedition activity but have yet to work this one. Perhaps all this one will take is paying more attention. It shouldn't be difficult to work.
3Y Bouvet and 3Y Peter I: These Antarctic islands are remote and battered by severe sea and weather conditions. There was one recent DXpedition attempt to Bouvet island that failed to land due to the weather. I have both countries confirmed back in the 1980s. All one can do is wait for intrepid and well-financed DXpeditioners to make the attempt.
4U1UN United Nations: Only this summer has the station been rebuilt in compliance with the severe security regulations at the UN complex in New York. I have heard them weakly on 20 meters but not workable. New York is too close for reliable communication on the higher HF bands except by scatter and high power. I would be surprised if I don't have this one in the log by 2019.
7O Yemen, YK Syria: One word says it all -- war. Very sad and tragic, and these won't be resolved soon. Going back a few decades I have lots of cards from 7O and a few from YK. But for now they are not workable.
BS7H Scarborough Reef: For one elderly ham who lives nearby this is the only country he needs to have them all. Another longtime DXer of my acquaintance doesn't believe it'll ever be active again. I have no opinion. Even if it were active it would be very difficult to work during a solar minimum from this part of the world.
BV9P Pratas: Like Scarborough Reef I know little about this one. Both have flown under my radar since they appear to have become entities during my 20 years away from the hobby.
CE0X San Felix: I've worked CE0Y and CE0Z, yet failed to work this one. If there's been recent activity I've missed it since I keep confusing these Chilean islands, forgetting which is the one I haven't worked. Like many other entities I worked this one decades ago. I'll just have to pay closer attention to catch the next visitor to San Felix island.
EZ Turkmenistan: This former Soviet republic was uncommon but not rare back in the days of the USSR. Since then Turkmenistan has been jinxed with totalitarian rule. Although that is not necessarily incompatible with amateur radio, it is not the case here. There have been signs that the political situation may be improving. We can only wait.
FR/g Glorioso: Another rare island waiting for a group to launch a DXpedition. Again, all I can do is wait.
FR/t Tromelin: There was an excellent DXpedition a few years ago, one which I completely failed to work. It happens. At the time my antenna and power situation made it difficult. I will just have to wait for the next DXpedition, and that may be years away.
FT5W Crozet and FT5X Kerguelen: Like the US, France has become fiercely protective of the environment on isolated islands with unique flora and fauna. French hams have been trying and failing to gain permission to land on these islands. There is (was?) a ham on Crozet Island although I am only aware that he has worked /MM when asea, and I did work him there. But that doesn't count for DXCC.
HK0M Malpelo: No recent DXpeditions. As with some other environmentally sensitive islands permission to land and operate is not routine. I am unfamiliar with how restrictive Colombia is with respect to Malpelo island.
JD1 Minami Torashima: As with a number of entities on this list, there is occasional activity from this one. Unfortunately the path is not the easiest during a solar minimum and I have yet to catch up with them. I need propagation and activity to coincide, and to pay enough attention to notice when it does occur.
JX Jan Mayen: This one ought to be easy and there has been some activity. Maybe I just need to pay attention and try harder.
KH3 Johnston, KH4 Midway, KH7K Kure, KP5 Desecheo: Permission for Kure island was recently denied (again) and the others are similarly difficult. When DXpeditions are permitted I expect these to be relatively easy to work. Back in the 1970s and 1980s I worked Johnston and Midway islands many times, and Kure island at least once. I have never worked Desecheo island.
KH8 Swains: The propagation path is fairly easy, so all I need right now is a DXpedition. I can't recall whether there has been any recent activity from this Pacific island.
KH9 Wake: The K9W DXpedition was a good one for working what has become quite a rare DXCC entity. At the time I was running QRP and little antennas. The best I did was "VE3?" on 17 meters CW. Although there is a ham on Wake Island his activity level hasn't made it easy. In fact I've never heard him. It's likely I'll have to wait a number of years until another DXpedition is permitted.
P2 Papua New Guinea, XU Cambodia, XZ Myanmar VR2 Hong Kong: Southeast Asia is a difficult path from this part of the world. During the most recent solar cycle peak my station was tiny. Now that I have bigger antennas suitable conditions are elusive. I have heard activity from all of these countries, including a few big DXpeditions, but have not succeeded in getting through. They'll come to me eventually if I pay attention and make the effort.
P5 North Korea: The short bursts of activity that pop up at rare intervals have satisfied few DXers. Some have been doggedly persistent while most that have worked North Korea have simply been lucky. A difficult propagation path and little activity makes this a tough one for many, including me.
PY0S St. Peter & St. Paul Rocks: Another one waiting for a DXpedition. I don't recall there being one over the past 5 years.
ST Sudan: For a brief period after independence Z8 South Sudan was not difficult to work. However Sudan itself has been and continues to be hostile to amateur radio. This one will likely require a change in the political winds. Years ago I worked Sudan a few times.
SV/a: Mount Athos: I've heard more pirates than legitimate activity from Mount Athos. At the moment I am unaware of any activity at all. The one resident monk with a license is inactive and visiting hams have not been welcome.
T31 Central Kiribati: This one takes an DXpedition, but otherwise should not be difficult. Patience is a virtue.
VK0/m: Macquarie: No DXpeditions in the past few years and little ham activity from the occasional Australian stationed on the island. Despite the great distance this area of the world is not overly challenging to reach, even during a solar cycle minimum.
VP8/o: South Orkney:You would think that since I've worked the other and far more rare VP8 Antarctic islands such as South Sandwich and South Georgia this one would be easy. Sadly, no. To be honest I haven't paid much attention to which island is which and so I've missed a few opportunities.
VU4 Andaman & Nicobar: There have several DXpeditions to this entity. Although I've worked its neighbour VU7 numerous times, and once with QRP, this one has eluded me. I have tried though perhaps not as much as I ought to since I keep thinking there will be a next time. The path over the pole will be a difficult one for the next two years.
YI Iraq: Although there are hams currently active it has proved elusive. From what I can tell their stations are modest and difficult to work from here. A couple that have been heard were very weak and working Europeans.
YV0 Aves: There have been no DXpeditions recently, and this one is notable in that it requires cooperation of the Venezuelan navy. The most recent attempt was ultimately cancelled due to...reasons.
ZL8 Kermadec, ZL9 New Zealand Subantarctic islands: These entities see occasional activity but have not grabbed my attention sufficiently to make the effort to chase them.
ZS8 Prince Edward & Marion: These days about the only activity on this protected island group is when a ham is stationed on the island. Unfortunately activity over the past 5 years has been fleeting and I haven't made a great effort to track them down.
If you took the time to read this far it should be evident that I am not at all fanatical about DXing. I love it, yes, though not nearly to the degree of many others. Notice that for more than a few of the countries I've yet to work I cannot recall whether there has been any activity since 2013 when I returned to the hobby and chose to reset my DXCC count to zero.
Yet there are indeed quite a few of these DXCC entities that have been either completely or almost completely absent from the airwaves since 2013 and therefore impossible to work. For these it will take patience for the political situation to change, permission from the relevant government authorities or money and persistence to mount DXpeditions. I am in no great rush so I can wait.
For me chasing DX is a fun challenge though not an obsessive compulsion. With a little more dedication and persistence I can do better at working the less active and more distant entities that are in fact active from time to time. Whether I'll ever do so I just don't know. Towers and antennas, and of course contests, are more interesting to me.
Amateur radio is a big hobby with diverse activities to meet many tastes. DXing and the DXCC pursuit can be a small or large focus for each of us, and our interests change with the years. There are hams who will only turn on the rig when one of the few remaining entities they have yet to work comes on the air. That's an attitude I'll never understand. I just don't see the point.
Thursday, October 25, 2018
Sunday, October 21, 2018
Deja Vu: Planting Another Big Tower
I've been busy getting ready for the planting of my second big LR20 tower, among other urgent tasks to be complete this fall. The blog has not gotten my full attention so the pace of articles has slowed. This will continue for a while.
Earlier this week the tower was planted. Now I am waiting on the concrete to cure and the machine shop to fabricate a few needed items. Then I can proceed. With luck the tower will be up this fall. Luck includes good weather, friends to come out to help and no serious mishaps. It's doable.
This is my last big tower -- two is enough for me to do what I want without incurring excessive maintenance during my golden years. For those who have been following along, this tower was in my original site plan for this QTH, and is located within meters of that plan. The tower will be a nominal 140', and actually ~133', or 40 to 41 meters, taking into account section overlap for splicing and base pillar height. This is an excellent height for DX work since it is 1λ on 40 meters and 2λ on 20 meters, and not quite 3λ at the top of the mast for 15 meters.
Unlike the disaster that was the planting of the first LR20 tower this one took only 7 hours. That's remarkable. It is thanks to the presence of an old hand leading his large crew of four, lots of planning and preparation beforehand and a large measure of good luck.
While it might not seem necessary with this crowd in attendance I was very busy on site working and supervising work. I got a good deal on the crew since for most of them it was their first time planting a guyed tower and my tower was a training exercise. Everyone wins. But the inevitable mistakes had to be noticed and pointed out, then corrected. Fortunately I have lots of management experience.
In this article I'll mainly focus on why the work went so well in comparison to the first big tower, which was a months long expensive headache. This should be more interesting to read about than simple repetition. There are relatively few pictures because I was less motivated to take them. The young guys on the crew took many more to, I suppose, remember what was for them a novel event.
First, the updated site plan. The changes are the approximate final positions of the new tower and the 80 meter array in the north field. Placing the new tower to meet my many requirements was difficult. The major impediment was avoiding the trees and rock wall surrounding the yard while achieving an ideal orientation of one tower face aligned with Europe for side mount yagis. A similar orientation on a line through the original big tower allows experimentation with wire antennas for the low bands.
I got pretty close to my objectives. A lesser objective was to minimize the transmission line run from the tower to the Trylon tower within the yard (yellow ellipse), which is the location of the antenna switch. The distance is similar to that for the other big tower, depending on how I ultimately choose to route the cables, both underground and above ground. There are several approaches to do this while avoiding tree roots and other obstacles. I have until next year to decide.
Surveying was similar to what I did for the first guyed tower. I'll refer you to that article rather than repeat myself.
Pretzel machine
Once again I opted to do my own rebar cages for the anchor and base. This time I had no outside help at all. I recruited material on hand to make the bending jigs and did a few tests to ensure each bend was exactly where I wanted them. I'm getting much better at this compared to the first time.
I again used an LR20 tower section and side mount bracket to build the jig for bending the rebar ties. I call it my pretzel machine. The design is an improvement over what I used before. It worked very well. The main challenge was determining how far the rebar would advance to the left as the hickey was rotated counter-clockwise on the leftmost stud. With that known it was easy to achieve consistent and accurate bends.
The circular stirrups were more of a challenge. The trick was to exploit the natural bend radius the jib imparted and repeatedly advance the rebar when the correct arc for a 12" circle was achieved. A circular template was used to check progress and to correct errors. The resulting stirrups aren't pretty but they're perfectly good.
When all was done I had 12 square pretzels, 18" on a side, and 5 circular pretzels of 12" diameter. Straight lengths of 20M rebar were cut and then combined with the ties and stirrups to form the 3 anchor cages and base pillar cage. The base platform grid is comprised of straight lengths of 20M rebar.
To bend the 20M bars for the base pillar (equivalent to US #6 bars) I needed a heftier jig. As in the past I recruited a suitable tree and steel pipes. After looking at several dozen trees (I have thousands on my property) I found a birch that was perfect. With this jig the 8 bars for the pillar were given a 90° hook on the end for joining to the base platform grid.
Notice the construction of the completed anchor cage. There are extra bars on the top and front that assist with distributing the tension of 4 guys across the load bearing faces of the anchor. Without them there is a risk that the concrete could split in the middle under severe wind load.
The cage is 18" × 18" × 90". This leaves a minimum 3" of concrete on all sides for the 2' × 2' × 8' reinforced concrete anchors. This is standard procedure to ensure long term corrosion protection of the rebar.
Excavation
I had a chance to chat with the backhoe operator before the tower crew arrived. He looked and sounded familiar. I soon realized that he was the plumber who came to my rescue when the house pressure system failed soon after I moved in. Turns out he had been laid off and returned to his earlier job as a backhoe operator.
While this is an interesting story what was more important is that I admired the skill and meticulousness he demonstrated on the plumbing job. He brought the same attributes to this job. There are ways to use a backhoe that can greatly improve the excavations, if the operator cares enough and has the requisite skill. This was my lucky day.
Knowing that the anchor holes were to be 2' × 2' × 8' he brought a 2' bucket on the front. He was able to made these 3 excavations between 24" and 27" wide. That's excellent. This was so accurate that I had to get the crew to use their shovel to clear 3" around all sides of the rebar cages, including squaring the bottom corners. There was little margin for error with this quality of backhoe work.
The advantage is that the quantity of concrete was kept to a minimum, which saved me a few hundred dollars. While it is possible to build casings for the anchors it is more costly in labour and materials, and if the casing is to be removed it is necessary to bring back the backhoe a day or two later to backfill the holes. Using what they call "mud holes" is faster and cheaper. But to do it you need the right soil and soil conditions and a good backhoe operator. On this day everything went right. Casing was only used for the base.
Concrete
Readers may remember the fiasco with concrete delivery for the first big tower. The truck got stuck in the boggy November hay field. It and the concrete had to be rescued by backhoe. I had no intention of letting that happen again.
When the driver arrived we did a walkabout to decide what to do. The backhoe has a big bucket (front end loader) for concrete delivery, if necessary.
The driver declared the ground just fine and drove onto the hay field. His judgment was good. Despite the 5 m³ of concrete onboard there were only light indentations left in the field.
Delivering the concrete direct to the excavation by chute is by far the superior method of delivery. It avoiding shifting of the steel when dropping concrete from the bucket and leaving time to push concrete into all the nooks and crannies to minimize air pockets. It is also much faster.
A handheld electric concrete vibrator made it easy to encourage the concrete to flow into all those spaces and level the surface. There is also less risk of shifting the rebar when shovels are used to pump the concrete.
Alignment
The crew did not spend time checking my surveying. There was no need. The crew leader aligned the anchor rods the old school way, with a string. In his experience it's the fastest and most reliable way of doing it. Too often he's found that transits are out of calibration or improperly used, but a string never lies.
When I did my surveying I measured the levelness of the ground. In one case I adjusted the distance to the anchor to account for the 18" drop in that direction. This ensures that the angle of all guys of each set come down from the tower at the same angle. My low tech method was to use a long level on a platform at the future position of the base pillar. Point it to a marked stake at the anchor site, ensure the level is level, then sight along it to measure the elevation difference.
More modern tools were used to set the 38° angle of the anchor rods. Every member of the crew would pull out their smart phones, lay them on rods and use inclinometer apps to adjust the angle. The angle was checked during and after the concrete pour.
The rule of thumb I was taught was that there are 30 minutes after the concrete is poured to move and align the anchor rods. Allow 2 hours before back filling over the exposed concrete, which allows it to firm up.
Back fill
When all but the back filling was complete the crew left, leaving me and the backhoe operator. While we waited for the concrete to firm up I had him move dirt around. This was the excess soil and subsoil from the excavations displaced by the concrete.
Some was left in small piles at the four excavations. I will use those to level the surface once the soil settles. That will take until spring. Since I forgot to leave extra soil at the excavations for the first big tower I also had him leave some at those four locations. I had done some wheelbarrow work in the spring but gave that up since it was tedious manual labour.
As the clock advanced we proceeded to back fill the three anchors. These were done in the same order they were filled with concrete and first poked to check firmness. He started slow with granular soil until the concrete was covered to 1' depth and the space under the anchor rods was filled. For the latter I used a shovel. This helped to prevent the weight of the back fill from pushing the rods downward to a lower than intended angle.
Over the next two days I spent a few hours raking and shovelling the extra soil. Large stones were removed by wheelbarrow. Last year I chose a spot within the bush to place the displaced soil and stones from the excavations.
Pier pin
The pier pin for the base section was embedded at the centre of the pillar soon after the concrete was poured. The pin in this case is a standard pipe with an OD ~1.3". The opening on the base section is 1.625". I may add a shim to fill the gap, however that is not really necessary.
One day later I filled the pipe with no-shrink grout and cleaned the pipe of stray grout and rust. It will be painted before the load bearing plate is slipped over the pin and grouted.
As you can see the 10' ground rod is already in. It was placed at a corner of the excavation then hammered down into the undisturbed soil. They crew would normally drive it below ground level and fill around it with gravel for future access. I prefer the ground rod to poke up a few inches. The difference in lightning protection is not large. I can drive it down later should I change my mind.
With that we're done! All that's left is final preparation of the tower sections and building upward. That stage of construction is scheduled after the CQ WW SSB contest. It should go faster than the first tower since the rigging can be reused and the lifting process has become routine. Hopefully I can get the same hams out to serve as ground crew. It's a race against winter.
Earlier this week the tower was planted. Now I am waiting on the concrete to cure and the machine shop to fabricate a few needed items. Then I can proceed. With luck the tower will be up this fall. Luck includes good weather, friends to come out to help and no serious mishaps. It's doable.
This is my last big tower -- two is enough for me to do what I want without incurring excessive maintenance during my golden years. For those who have been following along, this tower was in my original site plan for this QTH, and is located within meters of that plan. The tower will be a nominal 140', and actually ~133', or 40 to 41 meters, taking into account section overlap for splicing and base pillar height. This is an excellent height for DX work since it is 1λ on 40 meters and 2λ on 20 meters, and not quite 3λ at the top of the mast for 15 meters.
Unlike the disaster that was the planting of the first LR20 tower this one took only 7 hours. That's remarkable. It is thanks to the presence of an old hand leading his large crew of four, lots of planning and preparation beforehand and a large measure of good luck.
While it might not seem necessary with this crowd in attendance I was very busy on site working and supervising work. I got a good deal on the crew since for most of them it was their first time planting a guyed tower and my tower was a training exercise. Everyone wins. But the inevitable mistakes had to be noticed and pointed out, then corrected. Fortunately I have lots of management experience.
In this article I'll mainly focus on why the work went so well in comparison to the first big tower, which was a months long expensive headache. This should be more interesting to read about than simple repetition. There are relatively few pictures because I was less motivated to take them. The young guys on the crew took many more to, I suppose, remember what was for them a novel event.
First, the updated site plan. The changes are the approximate final positions of the new tower and the 80 meter array in the north field. Placing the new tower to meet my many requirements was difficult. The major impediment was avoiding the trees and rock wall surrounding the yard while achieving an ideal orientation of one tower face aligned with Europe for side mount yagis. A similar orientation on a line through the original big tower allows experimentation with wire antennas for the low bands.
I got pretty close to my objectives. A lesser objective was to minimize the transmission line run from the tower to the Trylon tower within the yard (yellow ellipse), which is the location of the antenna switch. The distance is similar to that for the other big tower, depending on how I ultimately choose to route the cables, both underground and above ground. There are several approaches to do this while avoiding tree roots and other obstacles. I have until next year to decide.
Surveying was similar to what I did for the first guyed tower. I'll refer you to that article rather than repeat myself.
Pretzel machine
Once again I opted to do my own rebar cages for the anchor and base. This time I had no outside help at all. I recruited material on hand to make the bending jigs and did a few tests to ensure each bend was exactly where I wanted them. I'm getting much better at this compared to the first time.I again used an LR20 tower section and side mount bracket to build the jig for bending the rebar ties. I call it my pretzel machine. The design is an improvement over what I used before. It worked very well. The main challenge was determining how far the rebar would advance to the left as the hickey was rotated counter-clockwise on the leftmost stud. With that known it was easy to achieve consistent and accurate bends.
The circular stirrups were more of a challenge. The trick was to exploit the natural bend radius the jib imparted and repeatedly advance the rebar when the correct arc for a 12" circle was achieved. A circular template was used to check progress and to correct errors. The resulting stirrups aren't pretty but they're perfectly good.
When all was done I had 12 square pretzels, 18" on a side, and 5 circular pretzels of 12" diameter. Straight lengths of 20M rebar were cut and then combined with the ties and stirrups to form the 3 anchor cages and base pillar cage. The base platform grid is comprised of straight lengths of 20M rebar.
To bend the 20M bars for the base pillar (equivalent to US #6 bars) I needed a heftier jig. As in the past I recruited a suitable tree and steel pipes. After looking at several dozen trees (I have thousands on my property) I found a birch that was perfect. With this jig the 8 bars for the pillar were given a 90° hook on the end for joining to the base platform grid.
Notice the construction of the completed anchor cage. There are extra bars on the top and front that assist with distributing the tension of 4 guys across the load bearing faces of the anchor. Without them there is a risk that the concrete could split in the middle under severe wind load.
The cage is 18" × 18" × 90". This leaves a minimum 3" of concrete on all sides for the 2' × 2' × 8' reinforced concrete anchors. This is standard procedure to ensure long term corrosion protection of the rebar.
Excavation
I had a chance to chat with the backhoe operator before the tower crew arrived. He looked and sounded familiar. I soon realized that he was the plumber who came to my rescue when the house pressure system failed soon after I moved in. Turns out he had been laid off and returned to his earlier job as a backhoe operator.
While this is an interesting story what was more important is that I admired the skill and meticulousness he demonstrated on the plumbing job. He brought the same attributes to this job. There are ways to use a backhoe that can greatly improve the excavations, if the operator cares enough and has the requisite skill. This was my lucky day.
Knowing that the anchor holes were to be 2' × 2' × 8' he brought a 2' bucket on the front. He was able to made these 3 excavations between 24" and 27" wide. That's excellent. This was so accurate that I had to get the crew to use their shovel to clear 3" around all sides of the rebar cages, including squaring the bottom corners. There was little margin for error with this quality of backhoe work.
The advantage is that the quantity of concrete was kept to a minimum, which saved me a few hundred dollars. While it is possible to build casings for the anchors it is more costly in labour and materials, and if the casing is to be removed it is necessary to bring back the backhoe a day or two later to backfill the holes. Using what they call "mud holes" is faster and cheaper. But to do it you need the right soil and soil conditions and a good backhoe operator. On this day everything went right. Casing was only used for the base.
Concrete
Readers may remember the fiasco with concrete delivery for the first big tower. The truck got stuck in the boggy November hay field. It and the concrete had to be rescued by backhoe. I had no intention of letting that happen again.When the driver arrived we did a walkabout to decide what to do. The backhoe has a big bucket (front end loader) for concrete delivery, if necessary.
The driver declared the ground just fine and drove onto the hay field. His judgment was good. Despite the 5 m³ of concrete onboard there were only light indentations left in the field.
Delivering the concrete direct to the excavation by chute is by far the superior method of delivery. It avoiding shifting of the steel when dropping concrete from the bucket and leaving time to push concrete into all the nooks and crannies to minimize air pockets. It is also much faster.
A handheld electric concrete vibrator made it easy to encourage the concrete to flow into all those spaces and level the surface. There is also less risk of shifting the rebar when shovels are used to pump the concrete.
Alignment
The crew did not spend time checking my surveying. There was no need. The crew leader aligned the anchor rods the old school way, with a string. In his experience it's the fastest and most reliable way of doing it. Too often he's found that transits are out of calibration or improperly used, but a string never lies.
When I did my surveying I measured the levelness of the ground. In one case I adjusted the distance to the anchor to account for the 18" drop in that direction. This ensures that the angle of all guys of each set come down from the tower at the same angle. My low tech method was to use a long level on a platform at the future position of the base pillar. Point it to a marked stake at the anchor site, ensure the level is level, then sight along it to measure the elevation difference.
More modern tools were used to set the 38° angle of the anchor rods. Every member of the crew would pull out their smart phones, lay them on rods and use inclinometer apps to adjust the angle. The angle was checked during and after the concrete pour.
The rule of thumb I was taught was that there are 30 minutes after the concrete is poured to move and align the anchor rods. Allow 2 hours before back filling over the exposed concrete, which allows it to firm up.
Back fill
When all but the back filling was complete the crew left, leaving me and the backhoe operator. While we waited for the concrete to firm up I had him move dirt around. This was the excess soil and subsoil from the excavations displaced by the concrete.
Some was left in small piles at the four excavations. I will use those to level the surface once the soil settles. That will take until spring. Since I forgot to leave extra soil at the excavations for the first big tower I also had him leave some at those four locations. I had done some wheelbarrow work in the spring but gave that up since it was tedious manual labour.
As the clock advanced we proceeded to back fill the three anchors. These were done in the same order they were filled with concrete and first poked to check firmness. He started slow with granular soil until the concrete was covered to 1' depth and the space under the anchor rods was filled. For the latter I used a shovel. This helped to prevent the weight of the back fill from pushing the rods downward to a lower than intended angle.
Over the next two days I spent a few hours raking and shovelling the extra soil. Large stones were removed by wheelbarrow. Last year I chose a spot within the bush to place the displaced soil and stones from the excavations.
Pier pin
The pier pin for the base section was embedded at the centre of the pillar soon after the concrete was poured. The pin in this case is a standard pipe with an OD ~1.3". The opening on the base section is 1.625". I may add a shim to fill the gap, however that is not really necessary.
One day later I filled the pipe with no-shrink grout and cleaned the pipe of stray grout and rust. It will be painted before the load bearing plate is slipped over the pin and grouted.
As you can see the 10' ground rod is already in. It was placed at a corner of the excavation then hammered down into the undisturbed soil. They crew would normally drive it below ground level and fill around it with gravel for future access. I prefer the ground rod to poke up a few inches. The difference in lightning protection is not large. I can drive it down later should I change my mind.
With that we're done! All that's left is final preparation of the tower sections and building upward. That stage of construction is scheduled after the CQ WW SSB contest. It should go faster than the first tower since the rigging can be reused and the lifting process has become routine. Hopefully I can get the same hams out to serve as ground crew. It's a race against winter.
Tuesday, October 9, 2018
3-element 40 Meter Yagi on a 40' (12 m) Boom
My recent article about long boom yagis reminded me of an omission in my blogging practice. The 15 meter and 20 meter yagis had references to earlier articles or elsewhere so that readers could learn the details of design and performance. I did not do the same for the 40 meter yagis on a 40' (12 meter) boom.
The designs were done some time ago, which is probably why I forgot about them until then. Not long before I wrote that article I sent the EZNEC files to a ham in Europe who was inquiring whether I had a design handy for a 12 meter boom. But in that article I only mentioned them in passing. It is worth writing about them because they do have interesting performance characteristics in comparison to the usual 48' (14.7 meter) boom length commonly used for 3-element 40 meter yagis, including those with a fourth element (coupled resonator, OWA design).
Before diving in it is worthwhile to briefly recap a few points about 3-element yagi design.
Overview of the yagis to be compared
The 3-element yagi on a 48' boom in the ARRL Antenna Book is a useful baseline for comparison because of its balance between gain and SWR bandwidth. If that antenna interests you, look there because I won't get into the details here. To summarize, its 2:1 SWR bandwidth is ~200 kHz, gain rises from ~7.8 dbi at 7.0 MHz to ~8.7 at 7.3 MHz, and F/R is 21 db at 7.0 MHz, rises to 27 db at 7.1 MHz then falls to 12 db at 7.3 MHz.
The tuning spread of the parasitic elements is 15%, or ±7.4% of the design midpoint. I will use the latter convention in this article. It is not half of 15% since the exponential mean must be used. You get this with the square root of the ratio between the reflector and director lengths. This is good enough for our purposes though not absolutely precise since the tubing taper schedule has an effect.
For comparison, the 3-element yagi I discussed in an earlier article has a tuning spread of 6.4% to increase gain by ~0.5 db. F/B continues to be very good, although 2:1 SWR bandwidth is a little less than 200 kHz. With a coupled resonator added the SWR bandwidth is low from 7.0 MHz to 7.3 MHz.
Because reducing the boom length to 40' also reduces achievable gain I further tightened element tuning to 5.3%. This recovers much of the gain while sacrificing SWR bandwidth, as we'll see. The addition of a coupled resonator helps with the latter.
As you likely noticed I have reverted to English units for these yagis. I do this because the tubes and pipes I use are measured in these units and so I model the yagis accordingly. The figures on the left are the distances along the boom the elements are placed and the lengths of each half element. The addition of a couple resonator only affects the length of the driven element. Its length without the coupled resonator is in any case dependent on the matching network: gamma, beta, L-network, etc.
Half element tubing schedule is: 144" of 1.9" pipe; 96" of 1.5" tube; 66" of 1" tube; 66" of ⅞" tube and a variable length of ¾" tube. This is not likely how I would construct the elements. It was an experiment to determine how I could put my stock of aluminum pipe to good use. The idea was spurred by reading Dave Leeson's Physical Design of Yagi Antennas -- it's out of print but the author kindly sent me a copy. For other tapering schedules it is necessary to carefully scale the elements.
For interest I show the 4-element yagi element currents at a higher frequency to highlight one aspect of how the coupled resonator broadens the SWR bandwidth. With the coupled resonator tuned to a higher frequency its current dominates that of the driven element at the high end of the band. In a sense it becomes the driven element despite not being attached to the transmission line. Since it is offset toward the front of the yagi the gain and F/B are slightly affected at higher frequencies.
Performance comparison
In the chart I used the same colour lines for both curves of each antenna -- gain and F/B -- to make it easy to compare yagis. Gain and F/B ought to be easy to distinguish!
I chopped the top of the chart to further improve readability since F/B figures well above 30 db are very difficult to achieve in real antennas due to the precise cancellation of element fields required. It is sufficient to state that F/B is excellent over a portion of the band.
Gains of the 40' boom yagis are about 7.8 dbi at 7.0 MHz and 8.4 dbi at 7.3 MHz. Gains of their 48' boom sisters is a fairly consistent 0.7 db higher. That isn't a large sacrifice to make considering the substantial construction differences for equal robustness.
F/B is significantly better for the 40' boom yagis even though I hadn't planned for that. It may be that further tuning of the 48' boom yagis would erase some or most of the difference. Certainly the yagi in the ARRL Antenna Book does a little better than these gain optimized yagis.
With a fixed matching network the 2:1 SWR bandwidth of the 3-element yagi on a 40' boom is 180 kHz. That's good but not great. With a switchable L-network at the feed point it is possible to achieve a low SWR up to 7.25 MHz. Getting all the way up to 7.3 MHz would require one more switch position. I wouldn't bother though some might want it. At least in the Americas where we have a 300 kHz wide 40 meter band.
The coupled resonator version of the 40' boom yagi can achieve better than 2:1 SWR across the entire band. However I was unsuccessful bringing down the SWR lower than 1.4. Further tuning of the driven element and coupled resonator might do it, but there are no guarantees. My difficulty was exacerbated by NEC2 which has some difficulty correctly modelling the impedance of closely spaced elements even when great care is taken with element segmentation, as I did.
Perhaps in practice it'll do better than the model and can be tweaked once on the tower -- the driven element and coupled resonator are within easy reach. Otherwise it may be necessary to loosen the tuning of the parasitic elements to improve the SWR, at the expense of some gain. I did not explore this path for the present study.
Further work
Despite my best intentions I will not construct and raise a full size 40 meter yagi this year. Maybe not even next year. There is therefore time to play with the models and explore further options. For example, to give up some gain to recover SWR bandwidth. No matter what I do there will be have to be compromises made.
I hope the information in this article spurs a few ideas of your own. These antennas are far more challenging than the 40 meters wire yagis that have been so popular among the readers of this blog.
The designs were done some time ago, which is probably why I forgot about them until then. Not long before I wrote that article I sent the EZNEC files to a ham in Europe who was inquiring whether I had a design handy for a 12 meter boom. But in that article I only mentioned them in passing. It is worth writing about them because they do have interesting performance characteristics in comparison to the usual 48' (14.7 meter) boom length commonly used for 3-element 40 meter yagis, including those with a fourth element (coupled resonator, OWA design).
Before diving in it is worthwhile to briefly recap a few points about 3-element yagi design.
- Optimizing for gain only modestly reduces F/B but will significantly reduce the SWR bandwidth. The latter is due to the low radiation resistance associated with maximum gain.
- Frequency of maximum gain is above the usable bandwidth, while F/B tends to peak towards the low end of the usable bandwidth. In practical terms, a 3-element yagi typically has maximum gain on SSB and maximum F/B on CW.
- Designs which maximize SWR bandwidth sacrifice up to 1 db of gain. However F/B can remain good.
- Gain is optimized by bringing the self resonance of the director and reflector closer together. The spread in percentage is a convenient metric, one that I originally learned about in the venerable Yagi Antenna Design book by W2PV. Tuning of the driven element affects the match (and matching network) while having negligible effect on gain, F/B and SWR bandwidth.
- Best performance typically has the driven element offset toward the reflector end of the antenna a small amount.
Overview of the yagis to be compared
The 3-element yagi on a 48' boom in the ARRL Antenna Book is a useful baseline for comparison because of its balance between gain and SWR bandwidth. If that antenna interests you, look there because I won't get into the details here. To summarize, its 2:1 SWR bandwidth is ~200 kHz, gain rises from ~7.8 dbi at 7.0 MHz to ~8.7 at 7.3 MHz, and F/R is 21 db at 7.0 MHz, rises to 27 db at 7.1 MHz then falls to 12 db at 7.3 MHz.
The tuning spread of the parasitic elements is 15%, or ±7.4% of the design midpoint. I will use the latter convention in this article. It is not half of 15% since the exponential mean must be used. You get this with the square root of the ratio between the reflector and director lengths. This is good enough for our purposes though not absolutely precise since the tubing taper schedule has an effect.
For comparison, the 3-element yagi I discussed in an earlier article has a tuning spread of 6.4% to increase gain by ~0.5 db. F/B continues to be very good, although 2:1 SWR bandwidth is a little less than 200 kHz. With a coupled resonator added the SWR bandwidth is low from 7.0 MHz to 7.3 MHz.
Because reducing the boom length to 40' also reduces achievable gain I further tightened element tuning to 5.3%. This recovers much of the gain while sacrificing SWR bandwidth, as we'll see. The addition of a coupled resonator helps with the latter.
As you likely noticed I have reverted to English units for these yagis. I do this because the tubes and pipes I use are measured in these units and so I model the yagis accordingly. The figures on the left are the distances along the boom the elements are placed and the lengths of each half element. The addition of a couple resonator only affects the length of the driven element. Its length without the coupled resonator is in any case dependent on the matching network: gamma, beta, L-network, etc.
Half element tubing schedule is: 144" of 1.9" pipe; 96" of 1.5" tube; 66" of 1" tube; 66" of ⅞" tube and a variable length of ¾" tube. This is not likely how I would construct the elements. It was an experiment to determine how I could put my stock of aluminum pipe to good use. The idea was spurred by reading Dave Leeson's Physical Design of Yagi Antennas -- it's out of print but the author kindly sent me a copy. For other tapering schedules it is necessary to carefully scale the elements.
For interest I show the 4-element yagi element currents at a higher frequency to highlight one aspect of how the coupled resonator broadens the SWR bandwidth. With the coupled resonator tuned to a higher frequency its current dominates that of the driven element at the high end of the band. In a sense it becomes the driven element despite not being attached to the transmission line. Since it is offset toward the front of the yagi the gain and F/B are slightly affected at higher frequencies.
Performance comparisonIn the chart I used the same colour lines for both curves of each antenna -- gain and F/B -- to make it easy to compare yagis. Gain and F/B ought to be easy to distinguish!
I chopped the top of the chart to further improve readability since F/B figures well above 30 db are very difficult to achieve in real antennas due to the precise cancellation of element fields required. It is sufficient to state that F/B is excellent over a portion of the band.
Gains of the 40' boom yagis are about 7.8 dbi at 7.0 MHz and 8.4 dbi at 7.3 MHz. Gains of their 48' boom sisters is a fairly consistent 0.7 db higher. That isn't a large sacrifice to make considering the substantial construction differences for equal robustness.
F/B is significantly better for the 40' boom yagis even though I hadn't planned for that. It may be that further tuning of the 48' boom yagis would erase some or most of the difference. Certainly the yagi in the ARRL Antenna Book does a little better than these gain optimized yagis.
With a fixed matching network the 2:1 SWR bandwidth of the 3-element yagi on a 40' boom is 180 kHz. That's good but not great. With a switchable L-network at the feed point it is possible to achieve a low SWR up to 7.25 MHz. Getting all the way up to 7.3 MHz would require one more switch position. I wouldn't bother though some might want it. At least in the Americas where we have a 300 kHz wide 40 meter band.
The coupled resonator version of the 40' boom yagi can achieve better than 2:1 SWR across the entire band. However I was unsuccessful bringing down the SWR lower than 1.4. Further tuning of the driven element and coupled resonator might do it, but there are no guarantees. My difficulty was exacerbated by NEC2 which has some difficulty correctly modelling the impedance of closely spaced elements even when great care is taken with element segmentation, as I did.
Perhaps in practice it'll do better than the model and can be tweaked once on the tower -- the driven element and coupled resonator are within easy reach. Otherwise it may be necessary to loosen the tuning of the parasitic elements to improve the SWR, at the expense of some gain. I did not explore this path for the present study.
Further work
Despite my best intentions I will not construct and raise a full size 40 meter yagi this year. Maybe not even next year. There is therefore time to play with the models and explore further options. For example, to give up some gain to recover SWR bandwidth. No matter what I do there will be have to be compromises made.
I hope the information in this article spurs a few ideas of your own. These antennas are far more challenging than the 40 meters wire yagis that have been so popular among the readers of this blog.
Sunday, September 30, 2018
80 Meter 3-element Vertical Yagi: First Light
Much to my surprise I have been making slow and steady progress on my 3-element vertical yagi for 80 meters. I have many projects competing for my attention. Although significant work remains to see this project to completion there is finally enough in place to give it a actual on the air test. It is time for an update.
When I last visited this antenna the central full size vertical was built, with enough radials (34, with 700 meters of wire) that it easily became my antenna of choice for DX on 80. During September I did the following:
A set of 8 radials for each parasite was laid down before the elements were raised. They are each 15 meters long except for the one that ties the radial hubs for the parasite and the driven element. In earlier articles I described my radial system topology as overlapping rather than connected at busses placed between the 5 elements in order to reduce the work of soldering radials to busses at the expense of more radial wire.
After the parasitic elements were installed the impedance was measured and the radials increased to 16. The impedance was again measured to determine the trend toward non-resonance in the radial system, which strongly depends on the ground's dielectric constant and thus the velocity factor.
The EZNEC medium ground model for 20 meter long radials is a very close fit to what I measured: ~40 kHz increase in resonant frequency when the radial count increased from 8 to 16. I can now adjust the elements confident that I can predict what will happen should I add more radials later. Apparently the velocity factor with on-ground and shallowly buried radials is substantially lower than in the model. This isn't surprising since it is difficult to accurately model radials of this type with NEC2. In part because they must be perched a fraction of a wavelength above ground, where less of the field flows through the ground.
Before proceeding with tuning I added 2 more radials to each parasitic element, for a total of 18. These are wires running the ~15 meters distance between each of the 4 parasitic element radial hubs. Although the change in impedance was negligible this should slightly reduce ground loss for the entire array, no matter the direction chosen, including the array's omni-directional mode.
I chose 15 meters as the radial length for two reasons: limit the overall area of the antenna to minimize the land taken from the haying operation, and; limit swings in parasite resonance as radials are added.
Parasitic wire elements
Designing the T-top wire elements was a challenge. This is an element topology that NEC2 is not able to model accurately. I knew this from the start, as I learned when I put up my 160 meter antenna last year. The second factor influencing resonance is the number and length of radials. The 8 radials in that antenna are 30 meters long, which is approximately the same as 15 meter radials on 80 meters, relative to wavelength. The resonant frequency is pulled downward.
For a single element antenna with a low feed point impedance the correction is as simple as an L-network. It doesn't matter that the antenna is not resonant since the network easily accommodates a non-zero reactance, and the efficiency is high if the resonant frequency isn't far off. For a yagi there is no forgiveness in tuning the elements; you must get it right.
As a guide I used the K3LR dimensions for a 160 meter version of this antenna which you'll find in ON4UN's Low-Band DXing book, version 5. With a bit of geometry and adjustment to fit the physical layout of my antenna I came up with dimensions for the T and the vertical. A little was then added to both to allow room to snip wire to reach resonance. The initial length of each leg of the T is 5.5 meters. The vertical is 12 meters, which includes an extra 0.5 meters for tuning purposes.
Two wire elements are visible in the photo above. Unfortunately you'll have to squint to see them. I didn't properly compensate for sag so the vertical segment drags on the ground. The centre junction is simply a stainless steel bolt which the wires wrap around and then snugged tight. It's lighter than an insulator and more secure than solder alone.
The ropes that form the top end of the catenaries for the wire elements were cut to length and installed when the stinger and top section were lifted. The elements were walked up the tower and connected and the bottom ropes tied to the anchors, located 25.5 meters from the tower. That's right at the edge of the radial system (10.5 meter element spacing plus 15 meter radial length) to minimize land use.
It took a couple of hours to adjust the tension of each rope to achieve the best compromise among element sag, force on the stinger and centering the stinger. Eventually I was done and ready to proceed to the next step: tuning the elements and lighting up the yagi.
Measure, measure, measure
As I said above, precision is of the utmost importance in getting a yagi working properly. To this end I was fastidious about measurements. A marked template was set up on the ground to ensure the wire for the 4 elements were cut to the exact same length. The wire elements are therefore identical. Exactly 3" of wire are wrapped around the insulator at each end of the T. When I tied the catenary ropes up the tower I made a mark on the tower where each T should terminate, which helped achieve symmetry. All element ground anchors are exactly the same distance from the tower.
Although opposite elements are, and must be 180° apart, adjacent elements are not 90° apart. This symmetry is necessary in a 4-square but not in the yagi. In yagi mode only two parasitic elements are in use. The other two are floated (disconnected from ground) making them non-resonant and effectively invisible. I used this feature to optimize array aiming for my geographic location. Floating works, as demonstrated by no change to driven element impedance when the parasitic elements were raised and left floating.
The feed point of each wire element is similarly identical with respect to radial hub and its support, switching system anchor, back plate and enclosure. Before tuning the elements I measured the resonant frequency of all 4 of them, once with 8 radials and again with 16 radials.
The resonant frequency was below the design objective of 3.680 MHz so that they can be cut to resonance. More important is that my fastidiousness resulted in a resonance spread among the 4 elements of only 20 kHz, or 0.6%. Notice that the resistance part of the impedance dropped 7 Ω with 16 radials. There is obviously more ground loss to be eliminated. I can probably bring the resistance closer to 20 Ω by doubling the radials. But that's another 1,000 meters of wire! Efficiency doesn't come easy.
To measure any element of the array, including the driven element (tower), all other elements must be floated. That is, the monopole and radial systems must be disconnected. Otherwise the mutual impedance will mask what is really going on. One of the jobs of the switching system will be to float elements that are neither directors nor reflectors for the selected direction. All parasitic elements are floated when the array is in its omni-directional mode.
Rough wiring the 3-element yagi
The next step is the fun part: lighting up the yagi. Since the most useful DX heading is towards Europe I rough wired the northeast element as a director and the southwest element as a reflector. Since I don't want to cut wire at this time I calculated the amount to shorten the element to resonate the director to 3.680 MHz and shaved the insulation of the wire at the appropriate position to expose a tap point. The ~40 cm of wire beyond the connection has negligible effect on element behaviour.
For the reflector I used a rough wound coil of AWG 14 wire from my junk box since it looked to be about the right size. I attached it and alternately squeezed and stretched the coil until it resonated at 3.450 MHz. This only took 30 seconds since the analyzer continuously recalculates the impedance. All I had to do was move my hands out of the way after each adjustment.
With the element tuned I temporarily completed the connections with wire nuts. I move the analyzer to the driven element and measured the impedance of my improvised 3-element yagi at 25 kHz intervals.
The resistance part of the impedance is about as expected. This clearly shows how important it is to achieve the lowest possible ground loss with the biggest radial system you can manage. Even with a ground loss as low as 5 Ω the loss can be -2 db. That's a lot.
The X value is not terribly important, provided its absolute value is not much higher than R. That helps to minimize matching network loss. However for now I am leaving the 4:1 SWR as is and correcting it with the rig's ATU. The estimated total transmission line loss is -2 db despite being almost 300' long. It isn't difficult to keep transmission line loss low at 3.5 MHz. Once the matching network is in place the loss should be better than -1 db.
Before going further it is worth a moment to talk about instrumentation. To achieve accurate and repeatable measurements it is important to have an analyzer with the requisite performance and to use it properly. The RigExpert AA-54 is quite good considering the price. There are better products on the market for a higher price.
I am not making any recommendation. Refer to detailed technical reviews such as those found in QST rather than rely on informal opinions of friends who may know even less than you.
The analyzer should be able to get the R and X values correct within a few ohms when the SWR is high, which most of the cheapest units cannot do. Not only is accuracy important but so is repeatability. That is, the values should be the same between readings, including readings made after the unit is turned off for a while and reconnected to the antenna under test.
Make sure your body is not influencing the measurement by moving around. Do the same for the analyzer itself, including when in your hand or supported elsewhere. Keep the test leads short or compensate for the length; better units can calibrate on the transmission line length, or use software such as TLW to convert the measured impedance to that present at the load.
Doing it right with a finicky antenna like this one can save you a lot of grief. Buy the best analyzer you can afford if you like experimenting with antennas. A 2-port VNA is favoured by those with a need to design and test more complex antennas or to analyze impedance transformation networks. A handheld unit like the RigExpert is perfect for me.
On the air
This article is being written after 3 evenings with the antenna in its hard wired direction to the northeast (Europe, North Africa and Indian Ocean). Not only has activity on 80 meters has perked up after the summertime lull there are several current DXpeditions roughly in that direction, including 9X0T and TO6OK. As always there are many Europeans active overnight and their sunrise.
When I first lit it up I was briefly disappointed. Switching from the inverted vee (now with an apex of 19 meters) to the vertical yagi the band noise dropped precipitously. It seemed that the antenna efficiency was low, so that the analyzer measurement might be hiding a deeper problem. Or, perhaps, the transmission line loss is higher than calculated. My worries dissipated when I tuned in a signal from Europe.
All European signals were stronger versus the inverted vee just as they were when the antenna was configured as an omni-directional vertical. But now the difference is substantially greater. I did extensive comparisons to ensure that Faraday rotation and other causes of QSB were accounted for by comparing through signal strength peaks and valleys. The improvement was consistent. However there is variation with different stations and path lengths. The variation -- elevation angle, polarization and skew -- demonstrates the value of having more than one antenna per band.
Signal differences were as little as 1 S-unit and as much as 4 to 5 S-units. That is promising. But what happened to the band noise? One hint was listening to W8 and W5 stations off the back of the yagi. The F/B is very good. Signals that were S-9 on the inverted vee would drop to S-3 or lower; as a vertical the difference was typically 2 S-units in favour of the inverted vee. What these differences are in decibels is hazardous to estimate since an S-meter is not a reliable instrument.
What appears to be happening is the attenuation of early fall atmospheric QRN from warmer locales south and southwest of VE3. The northern path to Europe is of course colder with less of the weather that contributes to noise. That is, the antenna has good directivity. I confirmed this by comparing reception against my 175 meter long northeast Beverage. The Beverage is still the better receive antenna, though by far less than with an omni-directional antenna.
Keep in mind that a well tuned 4-square can achieve similar or better F/B over a wider bandwidth than this yagi. I knew this before proceeding with this antenna. For me the ability to experiment and make a less expensive directive array of similar performance was a deciding factor.
I can see myself living with the yagi on 80 meters and reserving the Beverage and other planned receive antennas primarily for use on 160 meters. I have no plans for a directive transmit array for 160 meters, although that could change.
Up next
The switching units must now be assembled, installed and adjusted. The 4 parasitic element units must be identical to ensure identical performance, which is important when switching direction. This applies to the coils, relays, lengths and routing of internal wires. The unit at the driven element will contain the switching matrix, signal distribution and relays for the matching networks.
Most of this work can be done indoors. The only parts I have yet to order are the relays, which I have been researching. There are trade offs with respect to cost, power handling, RF isolation and current draw. A wrong choice is not a disaster since they are easy enough to access and replace. The switching matrix is built but not fully tested.
The driven element stinger may need to be replaced, if not this fall then next year. It is proving to be mechanically marginal when tension is put on the catenaries. I would like to take up more of the slack. Replacement would take a few hours and should only affect the L-network due to a change in the electrical length of the driven element.
I don't anticipate completion before November. There are too many other projects to be done this fall and this job can be done during the cold weather. I may even lay more radials before the snow flies.
With the rough wired yagi performing so well I am really looking forward to completing this project.
When I last visited this antenna the central full size vertical was built, with enough radials (34, with 700 meters of wire) that it easily became my antenna of choice for DX on 80. During September I did the following:
- Laid radials for the 4 parasitic elements.
- Designed, built and installed the T-loaded wire elements.
- Rough tuned the parasitic elements.
- Hard wired the northeast element as a director and the southwest element as a reflector.
- Put it on the air and compared it with the inverted vee.
A set of 8 radials for each parasite was laid down before the elements were raised. They are each 15 meters long except for the one that ties the radial hubs for the parasite and the driven element. In earlier articles I described my radial system topology as overlapping rather than connected at busses placed between the 5 elements in order to reduce the work of soldering radials to busses at the expense of more radial wire.
After the parasitic elements were installed the impedance was measured and the radials increased to 16. The impedance was again measured to determine the trend toward non-resonance in the radial system, which strongly depends on the ground's dielectric constant and thus the velocity factor.
The EZNEC medium ground model for 20 meter long radials is a very close fit to what I measured: ~40 kHz increase in resonant frequency when the radial count increased from 8 to 16. I can now adjust the elements confident that I can predict what will happen should I add more radials later. Apparently the velocity factor with on-ground and shallowly buried radials is substantially lower than in the model. This isn't surprising since it is difficult to accurately model radials of this type with NEC2. In part because they must be perched a fraction of a wavelength above ground, where less of the field flows through the ground.
Before proceeding with tuning I added 2 more radials to each parasitic element, for a total of 18. These are wires running the ~15 meters distance between each of the 4 parasitic element radial hubs. Although the change in impedance was negligible this should slightly reduce ground loss for the entire array, no matter the direction chosen, including the array's omni-directional mode.
I chose 15 meters as the radial length for two reasons: limit the overall area of the antenna to minimize the land taken from the haying operation, and; limit swings in parasite resonance as radials are added.
Parasitic wire elements
Designing the T-top wire elements was a challenge. This is an element topology that NEC2 is not able to model accurately. I knew this from the start, as I learned when I put up my 160 meter antenna last year. The second factor influencing resonance is the number and length of radials. The 8 radials in that antenna are 30 meters long, which is approximately the same as 15 meter radials on 80 meters, relative to wavelength. The resonant frequency is pulled downward.
For a single element antenna with a low feed point impedance the correction is as simple as an L-network. It doesn't matter that the antenna is not resonant since the network easily accommodates a non-zero reactance, and the efficiency is high if the resonant frequency isn't far off. For a yagi there is no forgiveness in tuning the elements; you must get it right.
As a guide I used the K3LR dimensions for a 160 meter version of this antenna which you'll find in ON4UN's Low-Band DXing book, version 5. With a bit of geometry and adjustment to fit the physical layout of my antenna I came up with dimensions for the T and the vertical. A little was then added to both to allow room to snip wire to reach resonance. The initial length of each leg of the T is 5.5 meters. The vertical is 12 meters, which includes an extra 0.5 meters for tuning purposes.
Two wire elements are visible in the photo above. Unfortunately you'll have to squint to see them. I didn't properly compensate for sag so the vertical segment drags on the ground. The centre junction is simply a stainless steel bolt which the wires wrap around and then snugged tight. It's lighter than an insulator and more secure than solder alone.The ropes that form the top end of the catenaries for the wire elements were cut to length and installed when the stinger and top section were lifted. The elements were walked up the tower and connected and the bottom ropes tied to the anchors, located 25.5 meters from the tower. That's right at the edge of the radial system (10.5 meter element spacing plus 15 meter radial length) to minimize land use.
It took a couple of hours to adjust the tension of each rope to achieve the best compromise among element sag, force on the stinger and centering the stinger. Eventually I was done and ready to proceed to the next step: tuning the elements and lighting up the yagi.
Measure, measure, measure
As I said above, precision is of the utmost importance in getting a yagi working properly. To this end I was fastidious about measurements. A marked template was set up on the ground to ensure the wire for the 4 elements were cut to the exact same length. The wire elements are therefore identical. Exactly 3" of wire are wrapped around the insulator at each end of the T. When I tied the catenary ropes up the tower I made a mark on the tower where each T should terminate, which helped achieve symmetry. All element ground anchors are exactly the same distance from the tower.Although opposite elements are, and must be 180° apart, adjacent elements are not 90° apart. This symmetry is necessary in a 4-square but not in the yagi. In yagi mode only two parasitic elements are in use. The other two are floated (disconnected from ground) making them non-resonant and effectively invisible. I used this feature to optimize array aiming for my geographic location. Floating works, as demonstrated by no change to driven element impedance when the parasitic elements were raised and left floating.
The feed point of each wire element is similarly identical with respect to radial hub and its support, switching system anchor, back plate and enclosure. Before tuning the elements I measured the resonant frequency of all 4 of them, once with 8 radials and again with 16 radials.
The resonant frequency was below the design objective of 3.680 MHz so that they can be cut to resonance. More important is that my fastidiousness resulted in a resonance spread among the 4 elements of only 20 kHz, or 0.6%. Notice that the resistance part of the impedance dropped 7 Ω with 16 radials. There is obviously more ground loss to be eliminated. I can probably bring the resistance closer to 20 Ω by doubling the radials. But that's another 1,000 meters of wire! Efficiency doesn't come easy.
To measure any element of the array, including the driven element (tower), all other elements must be floated. That is, the monopole and radial systems must be disconnected. Otherwise the mutual impedance will mask what is really going on. One of the jobs of the switching system will be to float elements that are neither directors nor reflectors for the selected direction. All parasitic elements are floated when the array is in its omni-directional mode.
Rough wiring the 3-element yagi
The next step is the fun part: lighting up the yagi. Since the most useful DX heading is towards Europe I rough wired the northeast element as a director and the southwest element as a reflector. Since I don't want to cut wire at this time I calculated the amount to shorten the element to resonate the director to 3.680 MHz and shaved the insulation of the wire at the appropriate position to expose a tap point. The ~40 cm of wire beyond the connection has negligible effect on element behaviour.
For the reflector I used a rough wound coil of AWG 14 wire from my junk box since it looked to be about the right size. I attached it and alternately squeezed and stretched the coil until it resonated at 3.450 MHz. This only took 30 seconds since the analyzer continuously recalculates the impedance. All I had to do was move my hands out of the way after each adjustment.
With the element tuned I temporarily completed the connections with wire nuts. I move the analyzer to the driven element and measured the impedance of my improvised 3-element yagi at 25 kHz intervals.The resistance part of the impedance is about as expected. This clearly shows how important it is to achieve the lowest possible ground loss with the biggest radial system you can manage. Even with a ground loss as low as 5 Ω the loss can be -2 db. That's a lot.
The X value is not terribly important, provided its absolute value is not much higher than R. That helps to minimize matching network loss. However for now I am leaving the 4:1 SWR as is and correcting it with the rig's ATU. The estimated total transmission line loss is -2 db despite being almost 300' long. It isn't difficult to keep transmission line loss low at 3.5 MHz. Once the matching network is in place the loss should be better than -1 db.
Before going further it is worth a moment to talk about instrumentation. To achieve accurate and repeatable measurements it is important to have an analyzer with the requisite performance and to use it properly. The RigExpert AA-54 is quite good considering the price. There are better products on the market for a higher price.
The analyzer should be able to get the R and X values correct within a few ohms when the SWR is high, which most of the cheapest units cannot do. Not only is accuracy important but so is repeatability. That is, the values should be the same between readings, including readings made after the unit is turned off for a while and reconnected to the antenna under test.
Make sure your body is not influencing the measurement by moving around. Do the same for the analyzer itself, including when in your hand or supported elsewhere. Keep the test leads short or compensate for the length; better units can calibrate on the transmission line length, or use software such as TLW to convert the measured impedance to that present at the load.
Doing it right with a finicky antenna like this one can save you a lot of grief. Buy the best analyzer you can afford if you like experimenting with antennas. A 2-port VNA is favoured by those with a need to design and test more complex antennas or to analyze impedance transformation networks. A handheld unit like the RigExpert is perfect for me.
On the air
This article is being written after 3 evenings with the antenna in its hard wired direction to the northeast (Europe, North Africa and Indian Ocean). Not only has activity on 80 meters has perked up after the summertime lull there are several current DXpeditions roughly in that direction, including 9X0T and TO6OK. As always there are many Europeans active overnight and their sunrise.
When I first lit it up I was briefly disappointed. Switching from the inverted vee (now with an apex of 19 meters) to the vertical yagi the band noise dropped precipitously. It seemed that the antenna efficiency was low, so that the analyzer measurement might be hiding a deeper problem. Or, perhaps, the transmission line loss is higher than calculated. My worries dissipated when I tuned in a signal from Europe.
All European signals were stronger versus the inverted vee just as they were when the antenna was configured as an omni-directional vertical. But now the difference is substantially greater. I did extensive comparisons to ensure that Faraday rotation and other causes of QSB were accounted for by comparing through signal strength peaks and valleys. The improvement was consistent. However there is variation with different stations and path lengths. The variation -- elevation angle, polarization and skew -- demonstrates the value of having more than one antenna per band.
Signal differences were as little as 1 S-unit and as much as 4 to 5 S-units. That is promising. But what happened to the band noise? One hint was listening to W8 and W5 stations off the back of the yagi. The F/B is very good. Signals that were S-9 on the inverted vee would drop to S-3 or lower; as a vertical the difference was typically 2 S-units in favour of the inverted vee. What these differences are in decibels is hazardous to estimate since an S-meter is not a reliable instrument.
What appears to be happening is the attenuation of early fall atmospheric QRN from warmer locales south and southwest of VE3. The northern path to Europe is of course colder with less of the weather that contributes to noise. That is, the antenna has good directivity. I confirmed this by comparing reception against my 175 meter long northeast Beverage. The Beverage is still the better receive antenna, though by far less than with an omni-directional antenna.
Keep in mind that a well tuned 4-square can achieve similar or better F/B over a wider bandwidth than this yagi. I knew this before proceeding with this antenna. For me the ability to experiment and make a less expensive directive array of similar performance was a deciding factor.
I can see myself living with the yagi on 80 meters and reserving the Beverage and other planned receive antennas primarily for use on 160 meters. I have no plans for a directive transmit array for 160 meters, although that could change.
Up next
The switching units must now be assembled, installed and adjusted. The 4 parasitic element units must be identical to ensure identical performance, which is important when switching direction. This applies to the coils, relays, lengths and routing of internal wires. The unit at the driven element will contain the switching matrix, signal distribution and relays for the matching networks.
 |
| QRP friends visiting the 80 meter array (Credit: VA3RKM) |
The driven element stinger may need to be replaced, if not this fall then next year. It is proving to be mechanically marginal when tension is put on the catenaries. I would like to take up more of the slack. Replacement would take a few hours and should only affect the L-network due to a change in the electrical length of the driven element.
I don't anticipate completion before November. There are too many other projects to be done this fall and this job can be done during the cold weather. I may even lay more radials before the snow flies.
With the rough wired yagi performing so well I am really looking forward to completing this project.
Friday, September 21, 2018
Useless Stuff
As a ham for over 45 years it is perhaps unsurprising that I have a large junk box. It's not really a box but rather dozens of boxes and piles of equipment and parts spread all over the place: basement, shack, garage and lurking among the trees. Some is little different than pure junk while others are fully functional though dated or with no foreseeable application.
Very little of my junk disappeared during the 20 years I was out of the hobby, or before or since for that matter. Since returning 5 years ago I have collected even more. Far more Storing, categorizing and finding stuff has been difficult. Not a week goes by that I don't find something interesting or valuable that I forgot that I had or didn't realize that I had it at all.
With that said I will now present a select set of junk that may induce nostalgia, bewilderment, "hey, I need one of those!" or violent disagreement over what, in fact, is junk or whether it can possibly have any use.
Heil headset
I purchased this headset over 30 years ago and I loved it. I still do. It's light, comfortable, and has a high talk power mic element.When the microphone cable became intermittent a few years ago and the ear pads deteriorated it was retired in favour of a modern headset. Here are the reasons:
When I bought this rig (used) in 1985 it was fabulous. The receiver was quiet and performed very well in comparison to competitors. It has a bit of a cult following. Unfortunately it does not work, suffering as it does from a pernicious design flaw: short life relays throughout.
Many have replaced the relays and continue the rig it to this day. But its time has passed. The transmitters are tubes that must be periodically replaced and frequency changes require manual transmitter tuning. The rig is not PC friendly, although there are ways to do it if you insist. Receiver performance is not comparable to the best modern rigs.
I can't bear parting with it and I also won't waste time fixing it. So it sits on a shelf. Behind it is a another useless item: a home brew power supply I built 30 years ago for a kilowatt 2 meter amplifier. The power supply works, the amplifier was never built and never will be built.
Magazines
I have come to despise paper. Whether it be logs, QSLs, newspapers, books or magazines. In this way I am quite modern. Before I moved from Ottawa 2 years ago I discarded over 40 years worth of ham radio magazines, catalogues, hamfest material and much more. Other than one big bundle of QSTs that I gave away to an interested ham it all got recycled. Well, except for one old issue of QST that had my picture in it.
If I need to look up an old article it is almost always accessible online. Most magazines I now get are electronic. Publishers that will insist on sending me paper magazines are magazines that I no longer subscribe to. Really, most of the subscription price is printing and postage, and the postage can be quite dear when sent from other countries. They are no longer worth the trouble, time or money.
I have a life ARRL membership so the QSTs keep coming, and they are once more accumulating. Before long I will once more be feeding the recycler.
Scrap hardware
When you have a fastener, clamp, clip or other bit of hardware is bent, rusted or of indefinite function what do you do with it. Provided it is somewhat usable I toss it into a box with similar stuff, roughly sorted by type. The rest goes into the garbage. I have even scooped up such stuff that other hams are discarding. I must have 100 lb or more of this scrap hardware.
I do this because of the many times I encounter an odd situation where I need an odd bit of hardware to accomplish a task but I don't want to waste or buy a new one. For example, old and rusty muffler clamps are used to jam a tube or pipe, or a perplexing plate with scattered holes in it becomes a shim or clamp washer, or a few old hose clamps are connected end to end lash a pipe to a tree or tower leg.
All of this scrap is stored outside or in the garage where there is lots of room and I don't care if it corrodes further. I often toss the stuff beyond the pale into the garbage bag when I root around for something useful.
Tuner
Flip through any ham magazine and you'll find many pages of advertisements for antenna tuners of all types and sizes. They can come in handy and for many hams with limited space they may be the only practical way to get on the air with whatever they are able to put up for an antenna. Tuners have occasionally found a use in my station over the years.
However tuners have their limits. While you may be able to transform most anything to 50 Ω it may be at the expense of efficiency. The cost can be exceptionally high, especially with short antennas on the low bands. As a contester I have additional concerns when it comes to tuning antennas since doing so costs valuable time even when the tuning is largely automatic.
Despite these qualms I still hold on to my tuners, large and small. Although I don't want to ever use one again I can't shake the feeling that one day in a pinch -- an antenna blows down in January when a rare DXpedition appears -- I absolutely have to have one.
Guy wire
I have a lot of guy wire. I have far more than I need or can ever hope to use. Most of it is used but is in excellent condition, whether from others hams or commercial surplus. Quite a lot of it I got for free.
The large quantity of guy wire in the picture is, unfortunately, truly useless except in the station of a truly extreme ham. I am unlikely to use it. The reason is that it is ⅜" EHS. That's heavier than you'd need on a big tower with stacked 40 meter yagis!
The reason it's useless is that guy wire must be tensioned to ~10% of breaking strength if it is to be taut enough to prevent excess tower motion or bending when the big winds hit. For this cable the breaking strength is 16,000 lb, so the pre-load tension is 1,600 lb. At each guy station on the tower that's 4,800 lb of force trying to tear the tower apart. There aren't many towers used by hams that are designed to withstand that radial and axial load.
On the other hand, well, you never know. Perhaps I'll find a use for it.
Rotator
This AR22 light duty rotator turned a Moseley TA-33jr on my first tower, back in the 1970s. For a television antenna rotator it struggled with a small tri-band yagi. Whenever the wind blew over about 60 kph (very common out on the VE4 prairie) the antenna spun and the rotator had to be recalibrated. But it was certainly inexpensive, perfect for a budding contester.
In addition to its low capacity it wasn't very robust. The controller's pulse-driven direction indicator uses a cheap electro-mechanical ratchet made of plastic and a spring that doesn't work well. It's one great feature is that you crank the dial to the desired direction, whereupon it starts up, turns, and shuts down when done. A harbinger of things to come in later years.
40 meter wire yagi
This antenna is proof that I have used low band wire yagis in the past, and that I not only design and write about them on this blog. This is a 2-element reversible inverted vee yagi I put up 30 years ago. The box contains the relays for the switching unit.
To simplify the antenna the driven element is fixed and the parasitic element is switched to be either a director or reflector. Well, this was 30 years ago and I didn't yet have a MiniNEC tool, nor did I appreciate the problems with this arrangement. When I fired it up I quickly learned why. The version you'll find on this blog is a far better design.
Despite its design problems it worked quite well. Although it'll never go up again I enjoy the memories whenever I come across it while I'm rooting through boxes looking for something.
Heliax connectors
I have been fortunate to find sources of used Heliax connectors at very good prices. They come available when commercial systems are decommissioned or the cables replaced. Among a bunch of connectors me and my hacksaw liberated last year were a couple of UHF female connectors for ⅞" Heliax. Those are rare and I was pleased with my good fortune. That changed when I got home and opened them up.
They are older than I realized. These connectors only fit the cable series that predates the LDF series. Connectors for the two series are not compatible since the older cable outer conductor has spiral corrugations while the LDF and AVA series have concentric corrugations. That's a shame.
Unfortunately the connectors have little use now because the ancient cable they are made for is rarely still in service. For now I can only admire them.
More obsolete equipment
Two years ago I made an effort, mostly successful, to clear out some useless stuff cluttering my basement by taking a table at a local flea market. The pictured items did not sell. I was not surprised. Despite working perfectly well they have little use today.
Packet radio is certainly around, though perhaps not so much at the data rates the PK-88 supports. The interest it received was no more than smiles for the memories it provoked. The high power low pass TVI filter has little purpose now that over-the-air (OTA) television reception is a rarity. It's good that TVI due to HF harmonics has been relegated to history, but then so is the TVI filter. It didn't get a second glance at the flea market. Both went back to the basement.
So much more
This sampling just scratches the surface. I didn't show my stock of ancient TTL logic chips and op amps, metal stock, short lengths of wire and rope, transformers, and so on. I suspect most of it will stay in boxes until after I'm gone when they'll finally go to the landfill. Indeed, that is also the likely fate of my towers and antennas if current trends in our hobby continue.
I do not keep the perpetually useless stuff for nostalgia or because I favour older generations of technology. I favour the march of technology, and that is what I aim for in my station. I will not buy and restore boat anchors, not even if I fondly look back on those products from my early days in the hobby. Others love doing that and I applaud their enthusiasm. But I won't even buy a paper book or magazine anymore.
Do I sell this stuff? Most of it has no value. Do I give it away? Most hams are in the same situation, having junk that they'll never use or need. Throw it out? I admit that it's hard to let go of stuff that maybe, just maybe will find a purpose someday. Part of my problem is that out here in the great emptiness I have far too much room to store the useless stuff hams tend to accumulate. So on it goes.
Very little of my junk disappeared during the 20 years I was out of the hobby, or before or since for that matter. Since returning 5 years ago I have collected even more. Far more Storing, categorizing and finding stuff has been difficult. Not a week goes by that I don't find something interesting or valuable that I forgot that I had or didn't realize that I had it at all.
With that said I will now present a select set of junk that may induce nostalgia, bewilderment, "hey, I need one of those!" or violent disagreement over what, in fact, is junk or whether it can possibly have any use.
Heil headset
I purchased this headset over 30 years ago and I loved it. I still do. It's light, comfortable, and has a high talk power mic element.When the microphone cable became intermittent a few years ago and the ear pads deteriorated it was retired in favour of a modern headset. Here are the reasons:
- Modern rigs have equalizers. A special "talk power" mic element is redundant. It is better to adjust the rig equalization once and then use any mic with a flat response.
- The mic element is dynamic. It can't easily be connected to a PC and some rigs only support high output electrets. Again, it is better in today's contesting shacks to stick with electret.
- Good quality PC gaming or VoIP headsets are inexpensive. Ham specific headsets are no longer necessary.
- I like open air ear pads despite not attenuating ambient sound. When I start doing multi-op contests from my station they will present a problem.
When I bought this rig (used) in 1985 it was fabulous. The receiver was quiet and performed very well in comparison to competitors. It has a bit of a cult following. Unfortunately it does not work, suffering as it does from a pernicious design flaw: short life relays throughout.
Many have replaced the relays and continue the rig it to this day. But its time has passed. The transmitters are tubes that must be periodically replaced and frequency changes require manual transmitter tuning. The rig is not PC friendly, although there are ways to do it if you insist. Receiver performance is not comparable to the best modern rigs.
I can't bear parting with it and I also won't waste time fixing it. So it sits on a shelf. Behind it is a another useless item: a home brew power supply I built 30 years ago for a kilowatt 2 meter amplifier. The power supply works, the amplifier was never built and never will be built.
Magazines
I have come to despise paper. Whether it be logs, QSLs, newspapers, books or magazines. In this way I am quite modern. Before I moved from Ottawa 2 years ago I discarded over 40 years worth of ham radio magazines, catalogues, hamfest material and much more. Other than one big bundle of QSTs that I gave away to an interested ham it all got recycled. Well, except for one old issue of QST that had my picture in it.
If I need to look up an old article it is almost always accessible online. Most magazines I now get are electronic. Publishers that will insist on sending me paper magazines are magazines that I no longer subscribe to. Really, most of the subscription price is printing and postage, and the postage can be quite dear when sent from other countries. They are no longer worth the trouble, time or money.
I have a life ARRL membership so the QSTs keep coming, and they are once more accumulating. Before long I will once more be feeding the recycler.
Scrap hardwareWhen you have a fastener, clamp, clip or other bit of hardware is bent, rusted or of indefinite function what do you do with it. Provided it is somewhat usable I toss it into a box with similar stuff, roughly sorted by type. The rest goes into the garbage. I have even scooped up such stuff that other hams are discarding. I must have 100 lb or more of this scrap hardware.
I do this because of the many times I encounter an odd situation where I need an odd bit of hardware to accomplish a task but I don't want to waste or buy a new one. For example, old and rusty muffler clamps are used to jam a tube or pipe, or a perplexing plate with scattered holes in it becomes a shim or clamp washer, or a few old hose clamps are connected end to end lash a pipe to a tree or tower leg.
All of this scrap is stored outside or in the garage where there is lots of room and I don't care if it corrodes further. I often toss the stuff beyond the pale into the garbage bag when I root around for something useful.
Tuner
Flip through any ham magazine and you'll find many pages of advertisements for antenna tuners of all types and sizes. They can come in handy and for many hams with limited space they may be the only practical way to get on the air with whatever they are able to put up for an antenna. Tuners have occasionally found a use in my station over the years.
However tuners have their limits. While you may be able to transform most anything to 50 Ω it may be at the expense of efficiency. The cost can be exceptionally high, especially with short antennas on the low bands. As a contester I have additional concerns when it comes to tuning antennas since doing so costs valuable time even when the tuning is largely automatic.
Despite these qualms I still hold on to my tuners, large and small. Although I don't want to ever use one again I can't shake the feeling that one day in a pinch -- an antenna blows down in January when a rare DXpedition appears -- I absolutely have to have one.
Guy wire
I have a lot of guy wire. I have far more than I need or can ever hope to use. Most of it is used but is in excellent condition, whether from others hams or commercial surplus. Quite a lot of it I got for free.
The large quantity of guy wire in the picture is, unfortunately, truly useless except in the station of a truly extreme ham. I am unlikely to use it. The reason is that it is ⅜" EHS. That's heavier than you'd need on a big tower with stacked 40 meter yagis!
The reason it's useless is that guy wire must be tensioned to ~10% of breaking strength if it is to be taut enough to prevent excess tower motion or bending when the big winds hit. For this cable the breaking strength is 16,000 lb, so the pre-load tension is 1,600 lb. At each guy station on the tower that's 4,800 lb of force trying to tear the tower apart. There aren't many towers used by hams that are designed to withstand that radial and axial load.
On the other hand, well, you never know. Perhaps I'll find a use for it.
Rotator
This AR22 light duty rotator turned a Moseley TA-33jr on my first tower, back in the 1970s. For a television antenna rotator it struggled with a small tri-band yagi. Whenever the wind blew over about 60 kph (very common out on the VE4 prairie) the antenna spun and the rotator had to be recalibrated. But it was certainly inexpensive, perfect for a budding contester.
In addition to its low capacity it wasn't very robust. The controller's pulse-driven direction indicator uses a cheap electro-mechanical ratchet made of plastic and a spring that doesn't work well. It's one great feature is that you crank the dial to the desired direction, whereupon it starts up, turns, and shuts down when done. A harbinger of things to come in later years.
40 meter wire yagi
This antenna is proof that I have used low band wire yagis in the past, and that I not only design and write about them on this blog. This is a 2-element reversible inverted vee yagi I put up 30 years ago. The box contains the relays for the switching unit.
To simplify the antenna the driven element is fixed and the parasitic element is switched to be either a director or reflector. Well, this was 30 years ago and I didn't yet have a MiniNEC tool, nor did I appreciate the problems with this arrangement. When I fired it up I quickly learned why. The version you'll find on this blog is a far better design.
Despite its design problems it worked quite well. Although it'll never go up again I enjoy the memories whenever I come across it while I'm rooting through boxes looking for something.
Heliax connectorsI have been fortunate to find sources of used Heliax connectors at very good prices. They come available when commercial systems are decommissioned or the cables replaced. Among a bunch of connectors me and my hacksaw liberated last year were a couple of UHF female connectors for ⅞" Heliax. Those are rare and I was pleased with my good fortune. That changed when I got home and opened them up.
They are older than I realized. These connectors only fit the cable series that predates the LDF series. Connectors for the two series are not compatible since the older cable outer conductor has spiral corrugations while the LDF and AVA series have concentric corrugations. That's a shame.
Unfortunately the connectors have little use now because the ancient cable they are made for is rarely still in service. For now I can only admire them.
More obsolete equipmentTwo years ago I made an effort, mostly successful, to clear out some useless stuff cluttering my basement by taking a table at a local flea market. The pictured items did not sell. I was not surprised. Despite working perfectly well they have little use today.
Packet radio is certainly around, though perhaps not so much at the data rates the PK-88 supports. The interest it received was no more than smiles for the memories it provoked. The high power low pass TVI filter has little purpose now that over-the-air (OTA) television reception is a rarity. It's good that TVI due to HF harmonics has been relegated to history, but then so is the TVI filter. It didn't get a second glance at the flea market. Both went back to the basement.
So much more
This sampling just scratches the surface. I didn't show my stock of ancient TTL logic chips and op amps, metal stock, short lengths of wire and rope, transformers, and so on. I suspect most of it will stay in boxes until after I'm gone when they'll finally go to the landfill. Indeed, that is also the likely fate of my towers and antennas if current trends in our hobby continue.
I do not keep the perpetually useless stuff for nostalgia or because I favour older generations of technology. I favour the march of technology, and that is what I aim for in my station. I will not buy and restore boat anchors, not even if I fondly look back on those products from my early days in the hobby. Others love doing that and I applaud their enthusiasm. But I won't even buy a paper book or magazine anymore.
Do I sell this stuff? Most of it has no value. Do I give it away? Most hams are in the same situation, having junk that they'll never use or need. Throw it out? I admit that it's hard to let go of stuff that maybe, just maybe will find a purpose someday. Part of my problem is that out here in the great emptiness I have far too much room to store the useless stuff hams tend to accumulate. So on it goes.
Monday, September 17, 2018
Challenges of Long Boom Yagis
The very biggest of the big guns put up large yagis for all the HF bands and then stack them for additional gain. This is neither easy nor inexpensive. To do it you either have money to spare or an especially strong motivation to pursue a few extra decibels. There is no one right answer. For someone like me, aiming high but not crazy high, trade-offs are necessary.
The above diagram from W2PV's Yagi Antenna Design is one I've shown before on this blog. It should be obvious that achieving an additional 3 db of gain by increasing boom length alone is exceedingly difficult on HF. Consider that a 1λ boom on 20 meters is almost 21 meters long (70'). Even at half that length on 10 meters it is still a giant. Hence stacking.
A long boom on HF yagis is rarely longer than 48' (14.7 meters). There are longer boom yagis out there, and even commercial products, but as I said they're rare. Given the incremental performance they are, in the opinion of many, not worth it. Consider that a 48' boom with a 3" diameter has a projected wind area of 12 ft². Treating it as a cylinder the wind load when broadside to a 135 kph (85 mph) wind is 240 lb. On 20 meters and up a long boom yagi has its maximum wind load in this orientation.
Building a long boom yagi to survive these and higher winds is expensive. The antenna will be very heavy to lift. The rotator and tower must be rated to deal with the load. Required boom strength increases faster than linearly with boom length due to the bending stress from the added wind load, its length and its weight. I need to keep the weight reasonable enough to allow tramming the antennas up the tower so that I can avoid the expense and land access issues of a large crane.
Since the gain of a 20 meter yagi with a 40' (12 meters) boom is only ~1 db lower than its 48' long bigger sibling I have chosen this length for my planned yagis. On 15 meters I am going shorter still: 32' (10 meters). For the next year or two, for the duration of the solar cycle minimum I will not be building long boom yagis for 10 meters. Should I decide to build 3-element yagi on 40 meters it will also use a 40' boom.
All of these antennas have been modelled and compared to longer and shorter boom yagis. The one for 15 meters was described in this blog quite some time ago. The 20 meter yagi is similar to the 5-element 40' boom yagi described in the ARRL Antenna Book. The 40 meter yagi is of my own design, both 3-element and with a coupled resonator for broadband low SWR. The latter antennas I will likely describe in a future article once the madness of tower and antenna building season subsides.
Few hams use yagis with booms longer than 6 to 8 meters and even these look big close up. The longer ones don't look so big when they're high in the air. On the ground you can better appreciate their size. In the picture you can see the first two long booms I built earlier this summer. Each is 3" diameter. The short one is 32', for the 15 meter yagi. The longer one is 41', for the 20 meter yagi. The garage they're in front of is 26' (8 meters) wide.
Both yagis come from 3" tubing I acquired a few years ago, with a heavy wall pipe inserted into the centre of the 40' boom. I took the pipe to a machine shop where they used a metal lathe to turn down the ends to fit within the 3" tubes. They did a very neat job and it was inexpensive. I mated the boom sections with the tools in my own workshop. The completed booms were set aside while I focussed on other projects.
Neither of these booms is sufficiently robust to be mounted high and rotated. I base this on calculation with software tools. The data say they can do the job, though without a margin for ultimate safety that I consider sufficient.
Instead these two yagis will be side-mounted, fixed on Europe and stacked with electrically identical yagis rotated at the top of the tower. The booms for the top yagis will be stronger, using aluminum I have on hand plus heavy wall tubing I will purchase. I am awaiting quotes on the element tubing (0.058" for telescoping) since of the many aluminum suppliers within driving distance none stocks this wall size. I have already bought the aluminum bar from which I will fabricate element-to-boom clamps.
None of this is cheap! That said, it is more economical than buying commercial products and I learn a lot along the way. The real cost is that it takes time. I may not get as far along as I'd like before winter with this and other projects. But it's fun, and that's as it should be. For 40 meters I would like to experiment with element design by building one and mounting it for use as a dipole during the winter and spring. This will help me assess its survivability before proceeding with yagi construction.
Long boom HF yagis have one other irritating feature: tuning. Unlike most 3 and 4 element yagis the driven element on a longer yagi is far from the centre. You cannot reach the driven element from the tower to adjust matching. For my 5-element 20 meter yagi on a 40' boom the distance between feed point and boom centre is 13' (4 meters).
Most commercial yagis tell you exactly what measurements to use, but on a home brew antenna a substantial amount of adjustment may be necessary. My plan is to mount each yagi vertically on a suitable tower (one without any antennas that can interact with the yagi) for tuning.
When I am done I will have one tall tower (the present one) dedicated to 40 and 10 meters and one dedicated to 20 and 15 meters. This is common practice for many contesters. One or two of my tri-band yagis will be fixed or rotatable to fill coverage gaps, especially for higher elevation angles to the Caribbean, the US and other paths when needed. Full implementation will take me into 2019.
Speaking of which, look at what showed up last week.
This is the tower for 20 and 15 meters. If all goes well it will be planted in the ground by early October. With luck and hard work it will be raised before winter. Assembly of the yagis will be done concurrently. Unfortunately I only anticipate raising the two side mounted yagis this year, with the rotatable antennas delayed to 2019. The weather will soon turn against me.
The above diagram from W2PV's Yagi Antenna Design is one I've shown before on this blog. It should be obvious that achieving an additional 3 db of gain by increasing boom length alone is exceedingly difficult on HF. Consider that a 1λ boom on 20 meters is almost 21 meters long (70'). Even at half that length on 10 meters it is still a giant. Hence stacking.
A long boom on HF yagis is rarely longer than 48' (14.7 meters). There are longer boom yagis out there, and even commercial products, but as I said they're rare. Given the incremental performance they are, in the opinion of many, not worth it. Consider that a 48' boom with a 3" diameter has a projected wind area of 12 ft². Treating it as a cylinder the wind load when broadside to a 135 kph (85 mph) wind is 240 lb. On 20 meters and up a long boom yagi has its maximum wind load in this orientation.
Building a long boom yagi to survive these and higher winds is expensive. The antenna will be very heavy to lift. The rotator and tower must be rated to deal with the load. Required boom strength increases faster than linearly with boom length due to the bending stress from the added wind load, its length and its weight. I need to keep the weight reasonable enough to allow tramming the antennas up the tower so that I can avoid the expense and land access issues of a large crane.
Since the gain of a 20 meter yagi with a 40' (12 meters) boom is only ~1 db lower than its 48' long bigger sibling I have chosen this length for my planned yagis. On 15 meters I am going shorter still: 32' (10 meters). For the next year or two, for the duration of the solar cycle minimum I will not be building long boom yagis for 10 meters. Should I decide to build 3-element yagi on 40 meters it will also use a 40' boom.
All of these antennas have been modelled and compared to longer and shorter boom yagis. The one for 15 meters was described in this blog quite some time ago. The 20 meter yagi is similar to the 5-element 40' boom yagi described in the ARRL Antenna Book. The 40 meter yagi is of my own design, both 3-element and with a coupled resonator for broadband low SWR. The latter antennas I will likely describe in a future article once the madness of tower and antenna building season subsides.
Few hams use yagis with booms longer than 6 to 8 meters and even these look big close up. The longer ones don't look so big when they're high in the air. On the ground you can better appreciate their size. In the picture you can see the first two long booms I built earlier this summer. Each is 3" diameter. The short one is 32', for the 15 meter yagi. The longer one is 41', for the 20 meter yagi. The garage they're in front of is 26' (8 meters) wide.
Both yagis come from 3" tubing I acquired a few years ago, with a heavy wall pipe inserted into the centre of the 40' boom. I took the pipe to a machine shop where they used a metal lathe to turn down the ends to fit within the 3" tubes. They did a very neat job and it was inexpensive. I mated the boom sections with the tools in my own workshop. The completed booms were set aside while I focussed on other projects.
Neither of these booms is sufficiently robust to be mounted high and rotated. I base this on calculation with software tools. The data say they can do the job, though without a margin for ultimate safety that I consider sufficient.
Instead these two yagis will be side-mounted, fixed on Europe and stacked with electrically identical yagis rotated at the top of the tower. The booms for the top yagis will be stronger, using aluminum I have on hand plus heavy wall tubing I will purchase. I am awaiting quotes on the element tubing (0.058" for telescoping) since of the many aluminum suppliers within driving distance none stocks this wall size. I have already bought the aluminum bar from which I will fabricate element-to-boom clamps.
None of this is cheap! That said, it is more economical than buying commercial products and I learn a lot along the way. The real cost is that it takes time. I may not get as far along as I'd like before winter with this and other projects. But it's fun, and that's as it should be. For 40 meters I would like to experiment with element design by building one and mounting it for use as a dipole during the winter and spring. This will help me assess its survivability before proceeding with yagi construction.
Long boom HF yagis have one other irritating feature: tuning. Unlike most 3 and 4 element yagis the driven element on a longer yagi is far from the centre. You cannot reach the driven element from the tower to adjust matching. For my 5-element 20 meter yagi on a 40' boom the distance between feed point and boom centre is 13' (4 meters).Most commercial yagis tell you exactly what measurements to use, but on a home brew antenna a substantial amount of adjustment may be necessary. My plan is to mount each yagi vertically on a suitable tower (one without any antennas that can interact with the yagi) for tuning.
When I am done I will have one tall tower (the present one) dedicated to 40 and 10 meters and one dedicated to 20 and 15 meters. This is common practice for many contesters. One or two of my tri-band yagis will be fixed or rotatable to fill coverage gaps, especially for higher elevation angles to the Caribbean, the US and other paths when needed. Full implementation will take me into 2019.
Speaking of which, look at what showed up last week.
This is the tower for 20 and 15 meters. If all goes well it will be planted in the ground by early October. With luck and hard work it will be raised before winter. Assembly of the yagis will be done concurrently. Unfortunately I only anticipate raising the two side mounted yagis this year, with the rotatable antennas delayed to 2019. The weather will soon turn against me.
Sunday, September 9, 2018
Chain Drive Prop Pitch Rotator
Even if you never lay eyes on a prop pitch motor and would never dream of or need a rotator of its capability it can teach lessons useful to many hams. I first saw a prop pitch motor up close and in action almost 35 years ago yet did not have one operating in my own station until last year. For what it's currently turning it is not strictly required but I expect that to change.
In this article I'll describe my prop pitch rotator system. I claim no credit for its design or construction since I purchased it secondhand. My job was to understand its mechanical and electrical details, then install and adjust it. I quite like it in all its "retro" awesomeness. I did have to design and build a direction indicator attachment to work with the home brew controller because most of it was missing.
While many hams who use a prop pitch motor opt for a simpler rotator system this one has several notable advantages. There are many ways to turn one of these beasts into a rotator.
Outboard mount
Use of a chain drive allows the motor to be installed with the shaft pointing down. This is advisable for unmodified prop pitch motors since the original gearbox lubrication is oil which can foul the electric motor and leave the gears dry when mounted with the shaft pointing upward under the mast. Replacing the oil with grease is strongly recommended for these reasons and because the oil will have dried or seeped out over the decades. The newest prop pitch motor was manufactured over 50 years ago!
With the shaft pointing down it is necessary to couple the motor shaft to the mast using a more elaborate system. Refer to the adjacent picture as I describe the system. For other pictures you'll be directed to follow the links to previous articles.
Unlike the typical rotator designed for amateur radio use a prop pitch motor is not designed to support the weight of a large mast and antenna system. When it is mounted under the mast it is mandatory to use a thrust bearing to support that weight. That leaves the motor to solely deal with torque, a job at which it is supremely capable.
It is not enough to simply wrap a chain around the mast and motor shaft. That would place an enormous radial load on the motor shaft which it cannot handle. A feature of the outboard mount is the elimination of these forces from being transferred to the motor.
Hanging beneath the top shelf (more detail on this will be shown below) is a mechanically robust open box that places a thrust bearing (for radial loads) above and below the gear that drives the chain. The bearings transfer the radial force to the tower and remove bending force from the motor shaft. The platform also supports the dead weight of the motor sitting on top.
The drive shaft in the tower has a similar arrangement with a bearing below the chain drive and another at the top of the shaft; the mast couples to the top of the drive shaft. I use this terminology to distinguish the mast (rotating antenna support) and drive shaft (part of the chain drive), although both can be though of as part of the mast.
The bearing under the drive shaft supports the full dead weight of itself, the mast and the antennas. It is a deep groove bearing designed for both axial and radial loads.
The collar on the drive shaft contains the cog gear for the chain and sits on top of the bearing. The drive shaft extends below the collar through the bearing for lateral support. See the article on mast construction for pictures.
All bearings are sealed. This is absolutely necessary since they won't last long in the weather without this feature. Additional weather covers are not required but can be helpful since sealing is never perfect and we want the bearings to last outdoors for many years of trouble-free service.
The photo shows the outboard mount from below, complete with an early version of the direction indicator subsystem. It gives a better idea of how massive and rigid it is. The system with its support struts weighs more than I do! That's without the motor attached. All the metal plate is ¼" galvanized steel. Joins are welded or made of ¼" angle stock. The top plate has an opening for the crown gear to mate with the prop pitch motor.
Chain system
The chain drive is quite simple. Standard size gears are welded to the motor shaft and the drive shaft and wrapped with a #60 (1") chain. The chain is stainless steel, and is highly recommended since access is limited for regular oiling. It's totally exposed to the elements. The rust you see in the pictures dripped from elsewhere. I cleaned and repainted the gears and other steel components that are not galvanized.
The number of links in the chain is adjustable. The chain has a master link. Without a master link a pin tool is needed to open and close the chain. A master link is the easier system to use. I did not need to change the number of links since my tower is the same as the previous owner's.
To avoid mishaps with the master link clips on top of the tower I raised and installed the chain with it wrapped around the motor shaft. When the drive shaft was dropped into place the chain was left loose around the bottom bearing. Only then did I wrap the chain onto the gears.
In the top picture you can see a ½" threaded rod on the bracket at the top of the platform. That and slots in the bracket are used to adjust the distance between the platform and the tower. Chain tension is determined by the distance.
I levered the chain onto the gears bicycle derailleur style after moving the platform inward as close as possible. It was then moved outward until the chain was taut. Looseness in the chain results in unwanted play in the mast that allows the wind to push the antennas back and forth several degrees. When properly adjusted the entire massive system can be easily spun by hand. When the motor is bolted on manual rotation is impossible.
Vertical alignment was a challenge. There is little room to adjust the vertical position of the motor platform. My first attempt resulted in chain binding on the drive shaft gear (see above). The only adjustment is the tower leg pinch clamp. Since there are no slots for the bolts on the platform's vertical struts the adjustment range is narrow. With some effort I was able to push the top of the platform down enough to allow the chain to move freely on the gears.
Control unit
The control unit is home brew, and although it shows its age it works well. Eventually I would like to replace it with software driven unit and only use the 24 VDC power supply to power the motor. My objective is a small desktop controller head, or eliminate it entirely with a PC application For the next year the project will remain low on my priority list.
The meter is obviously scrounged from an old CDR (now Hy-Gain/MFJ) rotator. There is an op amp circuit powered by +12 and -12 VDC that requires a linear potentiometer coupled to one of the rotating elements up the tower. The op amp circuit has two calibration pots: one to centre the meter and another to set the circuit's gain (degrees of rotation per ohm). Their settings are determined by the pot on the tower. The advantage is that almost any linear pot can be used. Mine is a multi-turn pot, identical to the one used by the previous owner, so that setup is not critical and allows > 360° of rotation. But don't try it unless the coax rotation loops are suitably designed.
I use Cat5 cable for the run up to the pot and 10/3 electrical cable to the motor. Except for part of the pot wiring both are burial grade and UV resistant.
Direction indicator
Of the two most common methods for sending direction data from the rotator to the control unit -- motor pulse generator and potentiometer -- a pot is the simpler method and will work with a greater variety of commercial control units. On the other hand a pulse generator has better long term reliability. A third method I learned about is a processor-based compass module to send direction data over wireless to a ground-based receiver.
I chose a pot since it's simple and my current control unit requires it. The first system I built (seen in an earlier picture) didn't survive long. First the wiring broke and later the ancient pot failed. The poor weatherproofing I hoped would last the winter didn't. But it was December, it was windy and cold on the tower, so I took my chances.
These 10K 10-turn linear pots are not cheap. Instead I ordered several from overseas at 10% the price. The downside was the long wait for the slow boat to arrive from China. When they arrived in August I got to work. This time I took the opportunity to improve the unit. After a couple of weeks in service it continues to work well. We'll have to wait and see how it does over the long term.
Some detail can be better seen in the earlier picture so refer to that as necessary. I chose the drive shaft to turn the pot. Common hardware store perforated steel strap holds the unit and has plenty of holes for attachment to the motor platform, bolt on the pot and tie the wires. The drive shaft coupling is made from strips of aluminum flashing (~0.03") and a hose clamp, with a ¼" screw to couple to the pot shaft.
The flashing was chosen so that perfect alignment between the drive shaft and pot is unnecessary. It will flex as the shaft turns. Silicone caulk keeps water out of the shaft coupler. Below that is a 1" circular plastic rain/snow shield cut from a food container and drilled at 15/64" to fit tight on the pot shaft. The shaft opening to the pot is coated with dielectric grease and the nut and lockwasher are caulked. The enclosure for the pot may look familiar: it's a cap from an empty WD-40 spray can.
The wiring tail is connected to the main cable run with crimp connectors. There are weatherproof commercial connectors available but this is easier to install and the wires can be cut and re-crimped easily. I enjoy the challenge of improvising with commonly available materials.
Lifting
Due to the weight and awkward dimensions of the motor platform I had to resort to alternative rigging. When all the tower sections were up the only parts of the platform installed were the support struts. These had to be installed during tower construction because they attach to two tower legs at the splice at the bottom of the top section. Once the top guys are tensioned those 4 bolts cannot be touched.
A heavy gauge steel strut was extended outward from the girt at the middle of the top section, which is several feet above the struts. The gin pole pulley was transferred to the lifting strut and the end of the strut was cable stayed. The rigging was tested to ensure it would support the load.
Using this rigging the bulky platform was lifted without being scraped along the side of the tower and tangling in the lower 3 sets of guys. The lifting strut swings laterally to help with levering the heavy platform around and onto the top surfaces of the support struts.
Despite the special rigging there was some difficulty maneuvering the platform into position. It required adjusting my safety restraints so that I could lean outward from the tower and apply the required muscle.
Once in position I secured the top of the platform to the tower legs with the pinch clamp. During motor installation, chain adjustment and electrical work the platform served as a handy shelf for tools and parts.
Spare motor
I was fortunate to be given a second working prop pitch motor when I purchased the system described in this article. My dilemma is whether to keep it as a spare or to custom build a clone of the motor platform for the second LR20 tower I am planning to raise.
The platform design makes it convenient to replace the motor. You remove the 6 bolts holding the motor to the platform and drop in the substitute. The chain must be tied when no motor is present to prevent the mast from freewheeling.
Wire splices between the motor tail and the main run are silicone-filled wire nuts designed for outdoor use. They are inexpensive and easy to use, and can be reused at least once if you are careful. You can see the nuts in the picture at the top of this article, before a weather cover was installed.
Building a platform for the second tower will require the services of a machine shop since I do not have the tools needed. Material, manufacture and galvanizing could be very expensive. I would also need to acquire a third prop pitch motor as a spare to ensure minimal disruption when a motor requires service.
A modern, high-capacity rotator may be the better choice. It will certainly work out cheaper. The decision can be put off for only a couple of months.
In this article I'll describe my prop pitch rotator system. I claim no credit for its design or construction since I purchased it secondhand. My job was to understand its mechanical and electrical details, then install and adjust it. I quite like it in all its "retro" awesomeness. I did have to design and build a direction indicator attachment to work with the home brew controller because most of it was missing.
While many hams who use a prop pitch motor opt for a simpler rotator system this one has several notable advantages. There are many ways to turn one of these beasts into a rotator.
Outboard mount
Use of a chain drive allows the motor to be installed with the shaft pointing down. This is advisable for unmodified prop pitch motors since the original gearbox lubrication is oil which can foul the electric motor and leave the gears dry when mounted with the shaft pointing upward under the mast. Replacing the oil with grease is strongly recommended for these reasons and because the oil will have dried or seeped out over the decades. The newest prop pitch motor was manufactured over 50 years ago!
With the shaft pointing down it is necessary to couple the motor shaft to the mast using a more elaborate system. Refer to the adjacent picture as I describe the system. For other pictures you'll be directed to follow the links to previous articles.
Unlike the typical rotator designed for amateur radio use a prop pitch motor is not designed to support the weight of a large mast and antenna system. When it is mounted under the mast it is mandatory to use a thrust bearing to support that weight. That leaves the motor to solely deal with torque, a job at which it is supremely capable.
It is not enough to simply wrap a chain around the mast and motor shaft. That would place an enormous radial load on the motor shaft which it cannot handle. A feature of the outboard mount is the elimination of these forces from being transferred to the motor.
Hanging beneath the top shelf (more detail on this will be shown below) is a mechanically robust open box that places a thrust bearing (for radial loads) above and below the gear that drives the chain. The bearings transfer the radial force to the tower and remove bending force from the motor shaft. The platform also supports the dead weight of the motor sitting on top.
The drive shaft in the tower has a similar arrangement with a bearing below the chain drive and another at the top of the shaft; the mast couples to the top of the drive shaft. I use this terminology to distinguish the mast (rotating antenna support) and drive shaft (part of the chain drive), although both can be though of as part of the mast.The bearing under the drive shaft supports the full dead weight of itself, the mast and the antennas. It is a deep groove bearing designed for both axial and radial loads.
The collar on the drive shaft contains the cog gear for the chain and sits on top of the bearing. The drive shaft extends below the collar through the bearing for lateral support. See the article on mast construction for pictures.
All bearings are sealed. This is absolutely necessary since they won't last long in the weather without this feature. Additional weather covers are not required but can be helpful since sealing is never perfect and we want the bearings to last outdoors for many years of trouble-free service.
The photo shows the outboard mount from below, complete with an early version of the direction indicator subsystem. It gives a better idea of how massive and rigid it is. The system with its support struts weighs more than I do! That's without the motor attached. All the metal plate is ¼" galvanized steel. Joins are welded or made of ¼" angle stock. The top plate has an opening for the crown gear to mate with the prop pitch motor.
Chain system
The chain drive is quite simple. Standard size gears are welded to the motor shaft and the drive shaft and wrapped with a #60 (1") chain. The chain is stainless steel, and is highly recommended since access is limited for regular oiling. It's totally exposed to the elements. The rust you see in the pictures dripped from elsewhere. I cleaned and repainted the gears and other steel components that are not galvanized.
The number of links in the chain is adjustable. The chain has a master link. Without a master link a pin tool is needed to open and close the chain. A master link is the easier system to use. I did not need to change the number of links since my tower is the same as the previous owner's.
To avoid mishaps with the master link clips on top of the tower I raised and installed the chain with it wrapped around the motor shaft. When the drive shaft was dropped into place the chain was left loose around the bottom bearing. Only then did I wrap the chain onto the gears.
In the top picture you can see a ½" threaded rod on the bracket at the top of the platform. That and slots in the bracket are used to adjust the distance between the platform and the tower. Chain tension is determined by the distance.
I levered the chain onto the gears bicycle derailleur style after moving the platform inward as close as possible. It was then moved outward until the chain was taut. Looseness in the chain results in unwanted play in the mast that allows the wind to push the antennas back and forth several degrees. When properly adjusted the entire massive system can be easily spun by hand. When the motor is bolted on manual rotation is impossible.
Vertical alignment was a challenge. There is little room to adjust the vertical position of the motor platform. My first attempt resulted in chain binding on the drive shaft gear (see above). The only adjustment is the tower leg pinch clamp. Since there are no slots for the bolts on the platform's vertical struts the adjustment range is narrow. With some effort I was able to push the top of the platform down enough to allow the chain to move freely on the gears.
Control unit
The control unit is home brew, and although it shows its age it works well. Eventually I would like to replace it with software driven unit and only use the 24 VDC power supply to power the motor. My objective is a small desktop controller head, or eliminate it entirely with a PC application For the next year the project will remain low on my priority list.
The meter is obviously scrounged from an old CDR (now Hy-Gain/MFJ) rotator. There is an op amp circuit powered by +12 and -12 VDC that requires a linear potentiometer coupled to one of the rotating elements up the tower. The op amp circuit has two calibration pots: one to centre the meter and another to set the circuit's gain (degrees of rotation per ohm). Their settings are determined by the pot on the tower. The advantage is that almost any linear pot can be used. Mine is a multi-turn pot, identical to the one used by the previous owner, so that setup is not critical and allows > 360° of rotation. But don't try it unless the coax rotation loops are suitably designed.
I use Cat5 cable for the run up to the pot and 10/3 electrical cable to the motor. Except for part of the pot wiring both are burial grade and UV resistant.
Direction indicator
Of the two most common methods for sending direction data from the rotator to the control unit -- motor pulse generator and potentiometer -- a pot is the simpler method and will work with a greater variety of commercial control units. On the other hand a pulse generator has better long term reliability. A third method I learned about is a processor-based compass module to send direction data over wireless to a ground-based receiver.
I chose a pot since it's simple and my current control unit requires it. The first system I built (seen in an earlier picture) didn't survive long. First the wiring broke and later the ancient pot failed. The poor weatherproofing I hoped would last the winter didn't. But it was December, it was windy and cold on the tower, so I took my chances.
These 10K 10-turn linear pots are not cheap. Instead I ordered several from overseas at 10% the price. The downside was the long wait for the slow boat to arrive from China. When they arrived in August I got to work. This time I took the opportunity to improve the unit. After a couple of weeks in service it continues to work well. We'll have to wait and see how it does over the long term.
Some detail can be better seen in the earlier picture so refer to that as necessary. I chose the drive shaft to turn the pot. Common hardware store perforated steel strap holds the unit and has plenty of holes for attachment to the motor platform, bolt on the pot and tie the wires. The drive shaft coupling is made from strips of aluminum flashing (~0.03") and a hose clamp, with a ¼" screw to couple to the pot shaft.
The flashing was chosen so that perfect alignment between the drive shaft and pot is unnecessary. It will flex as the shaft turns. Silicone caulk keeps water out of the shaft coupler. Below that is a 1" circular plastic rain/snow shield cut from a food container and drilled at 15/64" to fit tight on the pot shaft. The shaft opening to the pot is coated with dielectric grease and the nut and lockwasher are caulked. The enclosure for the pot may look familiar: it's a cap from an empty WD-40 spray can.
The wiring tail is connected to the main cable run with crimp connectors. There are weatherproof commercial connectors available but this is easier to install and the wires can be cut and re-crimped easily. I enjoy the challenge of improvising with commonly available materials.Lifting
Due to the weight and awkward dimensions of the motor platform I had to resort to alternative rigging. When all the tower sections were up the only parts of the platform installed were the support struts. These had to be installed during tower construction because they attach to two tower legs at the splice at the bottom of the top section. Once the top guys are tensioned those 4 bolts cannot be touched.
A heavy gauge steel strut was extended outward from the girt at the middle of the top section, which is several feet above the struts. The gin pole pulley was transferred to the lifting strut and the end of the strut was cable stayed. The rigging was tested to ensure it would support the load.
Using this rigging the bulky platform was lifted without being scraped along the side of the tower and tangling in the lower 3 sets of guys. The lifting strut swings laterally to help with levering the heavy platform around and onto the top surfaces of the support struts.Despite the special rigging there was some difficulty maneuvering the platform into position. It required adjusting my safety restraints so that I could lean outward from the tower and apply the required muscle.
Once in position I secured the top of the platform to the tower legs with the pinch clamp. During motor installation, chain adjustment and electrical work the platform served as a handy shelf for tools and parts.
Spare motor
I was fortunate to be given a second working prop pitch motor when I purchased the system described in this article. My dilemma is whether to keep it as a spare or to custom build a clone of the motor platform for the second LR20 tower I am planning to raise.
 |
| Spare prop pitch & drive shaft (right) posing with a Ham motor |
Wire splices between the motor tail and the main run are silicone-filled wire nuts designed for outdoor use. They are inexpensive and easy to use, and can be reused at least once if you are careful. You can see the nuts in the picture at the top of this article, before a weather cover was installed.
Building a platform for the second tower will require the services of a machine shop since I do not have the tools needed. Material, manufacture and galvanizing could be very expensive. I would also need to acquire a third prop pitch motor as a spare to ensure minimal disruption when a motor requires service.
A modern, high-capacity rotator may be the better choice. It will certainly work out cheaper. The decision can be put off for only a couple of months.
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