Tuesday, November 28, 2017

CQ WW CW: The Good and the Bad

CQ WW is arguably the biggest event on the contest calendar. My station was in poor shape for the SSB contest at the end of October and I hoped I'd have everything ready in time for the CW contest this past weekend. I didn't quite get there despite a big push in the final hours preceding the start of the contest on (our) Friday evening.

The most glaring hole in my station is that I was unable to run coax up to the yagis atop the big tower. You can see in the picture that they are up there sitting pretty, tuned and rotating, serving only to tease me. I ran out of time. At the last moment I had to choose between putting up a 40/80 inverted vee or one Heliax run. With nothing else for 80 meters I opted for the inverted vee.

In a way I'm complaining about nothing of importance. It's just that I know how much better I could have done had I completed the antenna work. As claimed score reports flood into 3830 it's clear that I did very well in comparison to others in my class and geographical region -- Single-op; All bands; Low power. Something worse happened to a local big gun who suffered a concussion that ultimately took him out of contention. I could only offer sympathy when we spoke before the contest. Health is more important than anything.

What follows is a detailed breakdown of my experience with the station as it was this weekend and what I learned. That will inform my future plans. I kept a notepad within reach with which to take notes so that I wouldn't forget. Items of significant importance I will delve into in future articles.

So sleepy

The rush of tower and antenna work left me exhausted. Climbing and working on towers is physically demanding, even more so in cold weather. When I sat down at the radio after the evening meal to configure the logging software and test the antenna switching I nearly fell asleep.

I made it through the first evening on caffeine. Since I needed sleep I missed the start of the 20 meter band opening Saturday morning. I didn't feel truly rested until Tuesday.


I put off buying a computer until the big sales immediately before the contest. The computer was already selected but deferred for the discount I was told was coming. Unfortunately it was out of stock when I did make the purchase on Thursday so I could only leave with the new display and accept delivery of the computer after the contest. However the discount was very attractive.

Instead I relied on my ancient laptop running Vista. The Wi-Fi is dead as are all but two USB ports. Since it decided to stop talking to my USB hub a few weeks ago I had to disconnect the mouse and had to deal with my palms riding the track pad while typing. That caused occasional odd behaviour in the logging software. The working USB ports were needed for the FTdx5000 and WinKeyer.

This PC is a liability since it doesn't have the RAM or processor capacity to open more than a few N1MM Logger windows, or windows that update frequently. For example, I cannot open the band map to see my self spots. Instead I relied on the rig's memories and VFOs to mark stations I wanted to work later.

Oddly enough the laptop chose the very next day to finally try to catch up with dozens of Microsoft updates that it seemed unable to process for several months. Perhaps it knew that it was about to be put out to pasture.

Inverted vee for 40 and 80 meters

Since I am behind in my project to build an 80 meter vertical array, and there is no feed line yet to the XM240 I decided to throw together a two-band inverted vee for 40 and 80 meters. It is a temporary antenna designed to get me through the winter season.

The core of the antenna is the 80 meter inverted vee I put up on the Trylon last winter. To this I added a 40 meter inverted vee I had on my tower back in Ottawa. That is, it's a fan wire antenna using PVC pipe sections to hold the wires ~18 cm (7") apart. The apex is ~32 meters on the big tower, a few meters below the Explorer 14. The ends are held down by rocks in the hay field, far enough out for the interior angle of the vee to be ~100°. If you look carefully you will see the tower mount in the picture above. The wire and spreaders are especially difficult to pick out.

There was no time to tune the antenna since it went up only hours before the start of the contest. We could do no more than put it in place, untangle the wires and connect a spare run of LMR400 to a 60 meter run of FSJ4 flexible ½" Heliax going back to the switch box.

As expected it tuned well on 80 meters but not on 40. Due to capacitive end effects between the higher band element and the longer one the 40 meter inverted vee is electrically longer and resonates below 7 MHz. In the minutes before the start of the contest I trained the rig's tuner throughout the 7.0 to 7.1 MHz band segment and did a quick comparison with the multi-band inverted vee on the Trylon.

For most DX the higher inverted vee was 1 to 2 S-units better. On US stations the lower one was equal or better on stations in the US northeast (very short path). The higher one was better on the majority of US stations. On 80 meters I had nothing to compare with other than the Beverage on receive, from which little or nothing can be concluded. I fared poorly on both 40 and 80 meters in the contest, apparently more due to propagation than my antennas since others suffered similarly.

The antenna works though obviously not so well as what I had planned for 80 meters and not what I should expect on 40 meters once the feed line is connected to the XM240. I estimate that I'll get another 2 S-units for the yagi from a combination of height and gain. The inverted vee is needed for the winter to provide an omni-directional option on 40 meters to switch to when needed. It will be interesting to compare when the 80 meter vertical comes online this winter.

Side mounted yagi to Europe

Most hams who put up a tri-bander have one similar in size to the Hy-Gain Explorer 14. The boom is short at only 14' (4.2 m), having 3 active elements on 20, 15 and 10 meters. If it's all you have it is possible to be perfectly happy with it and work the world; it performed well enough to help win two CQWW plaques for QRP contesting from Ottawa. When you have another antenna for comparison the compromises inherent in a short boom yagi become apparent.

The antenna is fixed at ~35 meters height and a heading of 45°, towards Europe. It is much higher than the only other high band antenna I had for the contest, a TH7 up 21 meters. Height helps though not as much as desired. Before the contest I rotated the upper yagis towards north to, in part, minimize any detrimental interactions between the still unusable TH6 and the Explorer 14. That both antennas use identical traps assists with a direct comparison since element loss is similar.

On 20 meters, there was little difference between the Explorer 14 and TH7 towards Europe. Although disappointing this should not come as a surprise. Yagi gain is primarily a function of boom length, not number of elements; both antennas have 3 active elements on 20 meters.

The picture changes on 15 meters. Despite the longer boom and an additional director on the TH7 the higher antenna is clearly superior by at least 1 S-unit. That was welcome since at this point in the solar cycle the European openings on 15 meters are not as strong or deep as other times. Regrettably there was no opening on 10 meter so that comparison was impossible.

F/B is poor enough on 20 and 15 meters that I could work many US and Caribbean stations while focussed on Europe. The price is increased QRM while running Europeans. On balance I can't decide whether this is a curse or a benefit.

This is a temporary antenna to get me through the winter contest season. Because my tower project lasted longer than expected I had to rely on the antennas that were close at hand. In the spring it comes down to be replaced by...something. I'll be exploring options over the winter based on my experience with a selection of yagis at different heights.

160 meters

My results on 160 meters were similar to 40 and 80 meters primarily due to poor conditions. I continued to do well in the pile-ups on DX towards the south and worked as far west as Hawaii. This was with a 3 db handicap since I had to dial back the FTdx5000 to 100 watts from 200 watts to qualify for the low power category.

What frustrated me was little success towards Europe during the contest, managing to work only a handful. Did the antenna have a serious failing despite modelling that showed only a modest impairment in that direction? I was relieved to discover after the contest that I was not alone, with everyone on this side of the Atlantic Ocean having the same experience.

The answer may be that QRM and noise levels happened to be worse than usual in Europe. After the contest those woes continued. I did manage to work 9G5W despite copying difficulty on their side of the QSO. It may be that my only permanent solution for top band success will be an amplifier.

Antenna switching

When I picked up a secondhand 2x8 antenna switch a few months ago I accelerated my plan for SO2R and remote switching. Although I fell far short of SO2R for this contest I did complete the basics for switching antennas.

All transmission lines terminate at a tower base where there is a housing for the switch. Control lines run back to the shack along with two runs of LMR400. This is mostly a temporary setup since the coax is not rated for burial.

Switching is entirely manual rather than rig or software controlled. I quickly built a control box with only one side active. The numerous "blanks" are there for future control of an 80 meter array direction and Beverage selection. Or I may go entirely software control.

I'll have more to say on antenna control and automation in future, which is a complex and important topic. For this contest I kept it simple, and it worked fine.

Empty calories

As the contest progressed and I knew that I'd fall short in my quest for multipliers I altered my strategy so that I could still turn in a competitive score. I didn't yet know that others were suffering similar propagation woes, and that the fault wasn't not entirely due to me or my half-built station.

With multipliers difficult to come by I spent many hours ignoring the chase entirely to instead park on a frequency and call CQ. My intent was to work as many US stations as possible, on every band that was open. These QSOs earn fewer points and are free of any multiplier value. For the Americans it's a win since they get an easy QSO in the log.

Since I look upon CQ WW as a primarily DX contest these QSOs feel a bit like the empty calories in our diets that frustrate nutritionists. They're filling but not optimal to our health. I appreciate every one of these QSOs yet feel that I'm missing out while I'm filling up the log. Yet it's a necessary step to a high score. Unfortunately for the US contesters it's an asymmetrical dynamic since they far outnumber Canadians. This is a contest in which scores between US and Canadian entrants are not comparable.

In between or even during runs I would check other bands for multipliers. This is how I worked a few unexpected multipliers on 10 meters, which was barely open, and then only occasionally.

Here, have a peanut

I'm the sort of person who is always snacking. Especially when the rate slows I am sorely tempted to run to the kitchen and grab something to eat. Since I've been gifted with a particular metabolism there is no threat of weight gain! However the temptation can impact results if it takes me away from the rig.

My solution is to keep a container of trail mix at hand. I use it as a reward system. If a run is going particularly well I'll grab a few seeds while the computer is sending a message. I'll eat a tastier nut when I score a multiplier.

It may seem silly but it works to keep me focussed and in the chair.


After a big contest I enter a several days long lull during which I tend to avoid getting on the air or doing anything radio related. Very soon I'll return to working on the station. It's a big, challenging project and it's clear that even with carefully thought out priorities I won't achieve all I planned in 2017.

Winter is an opportunity to relax, do a lot of operating and contesting and less challenging antenna work and improvements in the shack. I'll be busy without the same frenetic pace. At year end I'll do my usual annual review and look forward to the coming year. There's lots of hard work ahead, along with joy of learning and achieving my goals. 

Sunday, November 19, 2017

160 Meter Antenna, at Long Last

One of the great advantages of a big tower is that it is downright trivial to put up simple wire antennas that perform well. I have now built the 160 meter T-top vertical I modelled earlier, tuned it and put it on the air. It works great for a temporary antenna. Next year I'll roll up the radials and store the antenna during haying season.

Choosing a permanent high-performance 160 meter antenna is not a priority for this year or next. I hope to get to it eventually.

The picture of the upper part of the antenna is annotated since it is otherwise difficult to see the 14 AWG wires. With radials attached it resonates at 1.750 MHz. This is 80 kHz lower than in the model, or 4.5%. That's a lot! Using percentage is helpful since a few kHz of error is deceptively small at low frequencies. Perhaps there is more coupling to the tower or guy segments that the model dealt with, or perhaps the ground differs markedly that what is in the model or that NEC2 can accurately calculate.

For a single element antenna of this type the error is not critical -- there is no F/B or main lobe to optimize -- so I trimmed the 22 meter vertical wire down to the designed 21.5 meters and compensated the rest with an L-network. The L-network is required in any case due to the low radiation resistance. Low radiation resistance is a feature not a bug, as we'll see.

Design departures

I did not follow my original design exactly. The biggest change was to reduce the radial count from 16 to 8. For a temporary antenna I did not want to take more trouble than absolutely necessary to get an acceptable signal. The radials are as designed: 30 meters long. It only makes sense to go with longer radials -- λ/4 or more -- for a far greater number of radials.

Since the AWG 18 wire spools I ordered contain 150 meters of wire there are exactly 5 radials on each spool. I was surprised there was no overage on the spools. When I added short tails for wrapping the ends the fifth radial came up short 50 cm. It seems when you buy 150 meters of copper these days that's exactly what you get.

The catenary is tied off a couple of meters lower than the design to avoid crossing the prop pitch motor mount. This does not effect performance or the length of the vertical wire. All it does is move the ground anchor further out away.

I swung the antenna to be SSW of the tower rather than SW. The model shows that this change increases gain towards Europe (NE) almost 1 db. However it places the antenna wires, especially the T-top wires closer to the guys. As speculated above this may have caused the change in tuning. I did make sure to model the antenna wire as insulated -- which would lower the resonant frequency, as it measures in practice -- so that is not the cause of the difference.

First try

I planted a copper ground rod where the vertical wire hangs for easy radial attachment, wrapping the radial ends around a stainless hose clamp that holds them tight to the ground rod.

After the first 4 radials were laid I measured the impedance. This brought a surprise. The radiation resistance was almost 10 Ω higher than expected. Can you see why?

Suspecting the cause I returned to the computer to play with my EZNEC model. I added a direct connection to the MININEC ground through a resistance load representing a rough guess at the impedance of the ground connection through the ground rod. Sure enough the radiation resistance rose from 24 Ω to almost 33 Ω.

The purpose of the radials is to provide a low loss return path for the near field of the antenna and to keep those fields from circulating through the lossy ground. The ground rod routes a portion of the current directly via the ground. It's self defeating.

For my final design I replaced the ground rod with a short length of ABS pipe. The radials are attached in the same way. The difference is that the radials are now isolated from ground.

Measuring again, the radiation resistance dropped to 27 Ω at resonance. This is a significant improvement. Keep in mind we are trying to improve antenna efficiency, not add so much loss that there is a direct match to 50 Ω transmission lone. As I said above, a low radiation resistance is a good thing to see. The match comes later, in this case one day later.

L network

Once I had all the radials attached and the antenna tuned as much as possible without shortening the T-top I measured the impedance at 1.830 MHz, the centre of my CW contest and DX band segment, I sat down at the computer and designed the L-network. With modern software this is trivially easy. I used TLW to do this, as I have had good success with it for other antennas.

The 31 Ω resistance is several ohms higher than at the 1.750 MHz resonant frequency. Radiation resistance tends upward above resonance. Neither is the reactance a surprise since the antenna is long at 1.830 MHz. As you can see the feed point SWR is quite high primarily due to that inductive reactance.

I chose a "low pass" style of L-network since it offers modest attenuation of harmonics which could cause problems in a multi-op or SO2R contest setup; this is handy right now since I don't yet have band pass or notch filters. Experience tells me this is tolerable for 100 watts. Another benefit is that the coil size with this style of network is usually small.

I reused the L-network from the 80 meter tower vertical I had at my Ottawa QTH. I wound a new coil from insulated AWG 14 solid copper (bought in bulk) on a scrap piece of 1" PVC pipe (~1.3" OD). The wire's insulation makes the coil diameter slightly larger than the form.

For a capacitor I used a high voltage 2,200 pf disk ceramic. All the door knob capacitors I have are no more than 500 pf and if I add them in parallel there is no room for them in the small enclosure. The ESR of the chosen capacitor is probably not very low but based on the network design the power dissipation should be low when running my rig at maximum power of 200 watts. Next year I'll revisit this, or sooner if the capacitor fails.

Notice the SWR curve above. A computer, an hour in the workshop and a trip out to the field and the SWR is perfect. No further adjustment needed for an SWR of 1.0 at 1.840 MHz and a 2.0 SWR bandwidth of 100 kHz. I displayed my confidence up front by using fixed C and L components.

On the air

I had planned to leave it be for a couple of days to haul Heliax across the field and up the tower to get the other antennas connected. Then the weather closed in with freezing drizzle making the towers unapproachable. Instead I grabbed my newly connectorized rolls of LMR400 and a couple of UHF barrel connectors and made a 260' (80 m) run directly to the shack. Cable splices were propped up on spent wooden cable reels and tightly wrapped with plastic bags for temporary weatherproofing.

In the shack the SWR remained excellent. The bandwidth improved slightly, probably due to loss in the ancient bit of RG213 I grabbed to span the last 10 meters to the feed point. Then I waited for the sun to set.

There were a couple of European contests going on and I could hear them well on the northeast Beverage. On receive the vertical is of course far noisier. Even so many of the Europeans could still be heard well on the vertical, and not very well on the 40 meter inverted vee. My initial hypothesis is that the vertical is achieving lower radiation angles that allow it to hear DX better than the noise increase would suggest.

In other directions the impact was stark. My first QSO was TO2SP in the Caribbean, who was loud on the vertical. On the northeast Beverage his signal was almost unreadable. I had a similar result with US stations who were well over S9 on the vertical and extremely attenuated on the Beverage. The second night I worked J5T and pushed through a couple of small pile ups. That bodes well.

On a few DX stations far to the south they copied my 200 watts better than I copied them. That could pose a problem. Towards Europe and the Middle East I could copy signals quite well on the Beverage while they heard me not at all. It's a combination of not having an amplifier and, perhaps, poor receiving conditions on the other end.

Need...more...Beverages. But that's a winter project, not for now when more important antenna projects beckon. For the present I am very appreciative for what I have on 160 meters.

Obstacle course

I may have to move the radials this week for the remaining work on the tower. Since the antenna is only 20 meters from the big tower and the radials are 30 meters long there are many opportunities for accidents. I know where the wires are yet I have a habit of stepping on them. Others don't have even that foreknowledge.

In any case the LMR400 runs are needed for the two runs from the shack to the 8x2 switch I've installed away from the house (more on this in a future article). I can live without the 160 meter antenna for a couple of days. It's only real purpose for the next few days is to become familiar with how it performs and identify its capabilities on the air and any grievous deficiencies.

Once I've installed the intended 200' (60 m) coax to the switch box I'll weatherproof everything and leave it be for the winter. The next few weeks will tell me whether this antenna can deliver the results I want. First up is the CQ WW CW contest and then the ARRL 160 meter contest. I have high hopes for this, my first real antenna ever for top band. There are many things you can do on 50 acres that you cannot do on a suburban lot.

Thursday, November 16, 2017

Joy of Scrounging

Hams don't scrounge as much as they once did. I knew some incredibly successful scroungers when I was young (as most of us were), and at least one who turned it into a livelihood. Back then none of us had any money and we did what we could to find good deals on used and surplus equipment, sometimes from unconventional sources that might not know what they had and the value.

That is not the case today. The same hams are far older and have little reason to scrounge. It is said that the baby boom generation is the most affluent group in all of history. Indeed, many manufacturers and dealers have sprung up to help transfer some of that wealth into their products by offering high quality and expensive products and services to cater to them (us).

Not all are so well off. Besides which there is always the pleasure of the hunt, looking for and finding an elusive part or piece of equipment for a fraction of the new price. That is, the joy of scrounging. While I'm not as well off as some I am better off than most. I can afford to buy new most of the time yet I often prefer to scrounge. Finding a great deal can be as enjoyable as running across and working a new country (DXCC) or multiplier (contest).

Talking about coax and Heliax with one of the companies I have become familiar with brought about an opportunity recently. I have been busily testing and deploying Heliax and smaller coax and control cable to connect up those antennas I am rushing to get installed before CQ WW CW next weekend. As you may know Heliax and other high quality hard line is expensive and the connectors can be worse.

I have most of what I need for this fall though not what I need next year. Worse, the connectors I have already on the used Heliax or new in the box do not necessarily have a match. For example:
  • N connectors for LDF5-50A are mostly female yet I need male on some. The reverse is true of my stock of LDF4-50A! Gender adapters are in short supply in my junk box and good quality new ones are not cheap.
  • Andrew LDF has been out of production for 10 years. The cables and connectors are becoming harder to find, whether NOS (new old stock) or used and in good condition. N connectors are especially difficult to locate on the surplus market (new ones are still available), with most of what I'm finding being DIN 7-16. Surplus UHF are very rare. DIN is nice but connects to little that hams use. DIN connectors are only useful for splicing sections of Heliax.
  • Adapters between connector types -- UHF, N, DIN, etc. -- are expensive. I have exactly one DIN 7-16 to N adapter that I found at the Dayton flea market. I also find it difficult to know or predict which I'll need and of what gender. Often when I need a particular adapter I don't have one. The alternative is to prepare a short length of coax with a suitable connector on each end.
The outcome of that conversation came several days later when I drove home with a car full of coax, Heliax and used connectors.

It was not free, but the price paid was most attractive. I had to work for some of it when handed a hacksaw to saw connectors off cable ends.

In the picture are reel ends of LMR400 (Times Microwave) and equivalent cables from other manufacturers. There are several short rolls of LDF4-50A (with connectors) and a bunch of sawn off LDF5 and LDF4 connectors. Underneath the wooden spools is a box of other odds and ends. I also paid a good price for a handful of adapters and N connectors for LMR400.

I have some work to do before these Heliax connectors can be put to use. They must be removed from the cable ends and some require cleaning. Not all may be salvagable. To my surprise I even acquired a couple of Heliax UHF connectors, that most rare of items.

Tragically the cables the connectors came from were of no use. When a transmission line in commercial service is removed from a tower and equipment buildings it is not gently handled. That takes too much time and the used cable has little value to the companies involved. It is bent, folded and mutilated as it is cut down and thrown into trailers and transported for eventual disposal. Scroungers have to be nimble to receive any consideration. Since I'm not good at this I especially appreciate what I can find.

What I can't use I will likely gift to others. Not everyone buys new so I am sure I can pass around the joy.

Saturday, November 11, 2017

Big Mast for a Big Tower

The mast for my 150' tower is designed for the class of antennas I plan to put up there. Although the antennas will be modest for this winter season there will be bigger ones in future. I don't want to redo the job later if I can avoid it.

In this article I'll step through my design and construction of a mast that suits my needs. For this tower it is more involved than popping a short pipe through a bearing into a rotator and mounting a small yagi on top.What I came up with is not ideal yet suitable to my needs. Part of the challenge was making it compatible with the prop pitch motor/rotator with its chain drive.

Pipe mating

I am fortunate to have acquired two prop pitch motors and a chain drive system custom designed for my LR20 tower. It consists of an drive unit that attaches to the outside of the tower, a matching drive shaft (lower mast) for the the chain and two bearing plates. Altogether it weighs ~200 lb (90 kg)! It is perfectly capable of handling a full size 3-element 40 meter yagi.

The lower mast is a 3.5" diameter Schedule 40 pipe (3" IPS) that sits completely inside the tower. A mast must be fitted to it. The ID of the lower mast is 3.068" which would ideally suit a 3" diameter mast nesting inside it. However these are not often stocked locally. Instead I opted for the next smaller size of Schedule 40 pipe with a diameter of 2.875" (2.5" IPS).

Since transportation is difficult I bought the pipe from someone who would deliver at a modest price; many local steel suppliers don't deliver and I don't have a suitable vehicle of my own to do it. The galvanized structural pipe I got was 24' long and 0.25" wall. At 7 lb per foot it's quite heavy!

The lower mast comes with two sets of bolt holes to mate to the antenna mast. My job was to drill mating holes in the mast, and to do it so that the mast was perfectly straight. Even a small deviation would cause the mast to jam inside the bearings when rotated.

I improvised a jig to do the machining. Before cutting the total assembly is quite long at almost 30'. Setup was difficult due to the 170' weight of the new pipe! The lower mast is on the right, complete with cog for the chain drive and sleeve to sit on the lower bearing. The ungalvanized steel parts and cuts were cleaned and painted (or repainted) to protect against rusting.

It took awhile to get both pipes parallel and the smaller pipe centred in the larger one. I used a level on top and a straight edge on the sides to achieve this. Shims were used to centre the mast on the inside. I then only had to mark the spots for drilling the mast through the existing holes on the lower mast. I had liberally applied masking tape to the mast so that I had a good surface to mark up. (Note: the LR20 tower section is a recent acquisition that I used as part of the jig. Why I have it will be covered in a future article.)

All I had to do was slide the pipes apart and drill. Putting 17/32" holes through 0.25" of cylindrical steel is not easy to do on the ground with a hand drill! There was no convenient way to use a drill press. Plenty of drilling lube kept the bit and work from burning up. Splice hardware is ½" grade 5. The holes are slightly wider than ½" to ease insertion of the bolts through the two pipes.

Finally, after weighing the options, I chose to cut the mast so that 10' (3 meters) was exposed above the top plate. Why I chose this height is discussed below.

Adapting antenna to a 3" mast

Antennas going to the top mast required some modification. The boom-to-mast clamps on most commercial antennas will not fit a 3" mast. In my case that meant some metal work on the Cushcraft XM240 40 meter yagi and Hy-Gain TH6 tri-band yagi. The XM240 was taken off the Trylon in the spring in preparation for moving to the new tower. The TH6 was last used by me over 25 years ago. Both were refurbished for this project in addition to adapting them to the 3" mast.

Modifying the TH6 was the easiest. I ordered a selection of 3" clamps from DX Engineering to replace the stock Hy-Gain clamps for the boom and boom truss. The large saddle clamps are bolted directly to the boom splice plate, eschewing the Hy-Gain mast clamp.

Four holes for the saddle clamps were drilled through the plate. I wanted to reuse two of the holes but could not because that would place the new holes too close to the existing ones and therefore weaken the plate. I was careful to ensure the boom splice bolts would not interfere with the new clamps.

The mast will now be ~1" off centre. It's still well enough balanced that I did not bother with a counterweight on one side of the boom.

The truss plate was entirely replaced by a Cycle 24 muffler style clamp. Since they proved to be more robust than expected I chose to mount the guy turnbuckles eyes directly onto the ends of the u-bolt rather than machining a plate to fit onto the u-bolt. In the spring we'll see how that works out.

I modified the (provided by the previous owner) custom boom-to-mast clamp on the Cushcraft XM240 40 meter yagi to include an integrated truss support. This is necessary since the truss will extend above the mast. The reasoning is explained in the following section.

After fitting the DX Engineering 3" saddle clamps there was enough room on the side to attach a heavy gauge length of aluminum angle. I used what was available, but a pipe is a better (stronger) choice. Since the truss support is now off centre a small amount the length of the truss cables must be adjusted to fit.

The truss is tensioned on the ground rather than on the mast. The turnbuckles are unreachable when raised to its final position. This is a common technique I've seen at several large contest stations. I liked it so I borrowed it. The mast really needs to be at least 13' (4 meters) to support a boom truss for the top yagi. However this would add additional weight that is not needed, make the mast too long for my gin pole when lifted above the pipe's centre of gravity and climbing that tall a mast to install and service the yagi is unwelcome.

The tram line to raise the antenna actually runs between the boom and truss. Indeed, as I write this the XM240 has already been trammed onto the tower this way. But that's for another article.

Bearing plate

The tower came with a blank plate that is similar to the bearing plates that support the lower mast. I used power tools to grind off unwanted bits and accumulated rust. Once the upper mast was selected I ordered a similar industrial deep-groove bearing to act as a thrust bearing at the top of the tower. The lower mast bearings are NSK while this one is by FAG. All are sealed bearings, as are the bearings in the prop pitch chain drive unit. Weather covers are not mandatory but since they can be helpful I may add those later.

Deep groove bearings of this class are quite good for amateur applications. They have excellent specs for both axial and radial loads, which is unlike too many of the mast bearing marketed to hams. However they are not adjustable. The size of bearing must be carefully selected to fit the mast. This is not difficult since it happens that metric bearing sizes have just the right dimensions to suit common pipe sizes (IPS) used in Canada and the US:
  • 1.5" nominal (1.9"/48.3 mm OD): 50 mm bore / 0.85 mm gap
  • 2.5" nominal (2.875"/73.0 mm OD): 75 mm bore / 1.0 mm gap
  • 3" nominal (3.5"/88.9 mm OD): 90 mm bore / 0.55 mm gap
Often the gap between pipe and bearing can be left as is, especially for axial loads. I plan to add a shim to the 75 mm bearing on the top plate to reduce abrasion and chatter. Done this way the load is better distributed than bearings with set screws, and there will be no screws to loosen over time. Avoid exactly matching dimensions (e.g. 3" bore for a 3" OD pipe) since fitting may be difficult or even impossible when the pipe is galvanized or is painted.

A template for placing the bearing was made in much the same way as I did previously. First I confirmed that the plate fit the tower girt, found the centre and finally overlaid a trace of the bearing and the mounting hardware, all of which are shown above left. When all was aligned I drilled ½" holes through the ¼" steel plate and test fitted the bearing. It was then removed to paint the plate; the other bearing plates are galvanized, but not this one.

The bearing plate was slipped over the upper mast on the ground and lifted as a unit. The clamp keeping it there was the same one used to assist with the mating of the two masts. I had one oversight, forgetting that the bearing plate and the gin pole could not both be in the same place at the same time!

As a final note on the mast, I plan to add a conductive strap between the mast and tower. Although I don't intend to use this tower a 160 meter vertical (not compatible with SO2R and multi-op contesting) it will help drain static and avoid the possibility of rectification in the imperfect electrical contact via the bearings.

Raising, mating and alignment

A friend and his SUV once again provided the muscle to lift the masts. Their respective weights are approximately 75 lb and 100 lb, plus the bearing plates. The lower mast had to first be lowered into the tower so the upper bearing for the lower mast could be affixed, after which the lower mast was pulled up through the bearing and the lower plate attached. The upper mast was awkward due to its ~14' length, which even a tag line couldn't prevent from persistently catching on the top guys. This was easily resolved when I climbed the tower.

On the left you can see the clamp that stop the upper mast in the correct vertical position to drive home the bolts. The lower mast is rotated to get them aligned, assisted with tape markers on both pipes. With the clamp removed you can see that cross bolting the pipes is inadequate for keeping them concentric. The gap all around is ~3/32" (0.095").

This can only be resolved by filling the gap. When I couldn't easily locate 3/32" steel stock locally I noticed that the galvanized perforated strips I had in stock (and are found in hardware store everywhere) is 0.74" thick. That's a pretty good fit. All I had to do was cut several lengths, carefully curve them in my workshop and hook the end so they can't slide through.

On the tower I had little trouble pressing them down into the gap with the encouragement of a large wrench. Two of the shims are quite long, reaching down to the lower bolt to eliminate play at the bottom end of the upper mast. Once done and the upper bearing position tweaked the 200 lb of match spun easily in my hands. I already had the chain engaged, so the rotation included the prop pitch drive unit. The motor was added later since with it mounted the mast could only turn by powering the motor.

You may have also noticed that I replaced the splice bolts. The original 4" bolts were barely adequate to accommodate a nut and lock washer, and lock washers are not ideal for curved surfaces. The replacement bolts are 1" longer. The lock washer was replaced with a flat washer and locking is achieved with two nuts.

With that the mast was ready for the antennas to be raised.

Notes on mast strength

There seem to be two types of ham when it comes to selecting a mast: those who use whatever is at hand and those who must have the very best. A minority engineer the mast strength to the application. As to how strong a mast needs to be, well, it should as strong as it needs to be and no stronger. Not strong enough and disaster is awaiting its opportunity. Too strong adds unnecessary cost and difficulty.

I use a spreadsheet based on the ARRL mast strength calculator. The mast itself is nothing special, simply A53B grade. With my planned loads it is strong enough to survive 150 kph winds with the antennas I am mounting this winter. Next year there will be changes yet to be determined. In all likelihood I will end up with a better rating when a bigger yagi is mounted just above the top plate and a smaller yagi up top. I also have the option of substituting a larger mast.

Within reason I am not concerned about the load on the tower itself, which I know is perfectly up to the task of supporting a 3-element full size 40 meter yagi low on the mast. There is little bending moment for even a big antenna mounted close to the bearing plate, so a large diameter mast is to assure twisting strength (wind torque) and prevent slippage in the boom-to-mast clamps.

If the mast strength is not up the task -- wind load for your locale -- you have a few options:
  • Higher strength material: Although difficult or expensive to source a higher strength steel may be the best option. The yield strength of A53B class steel, the lowest and least expensive structural grade, can be doubled or tripled if you are willing to go that route.
  • Greater diameter: Increasing the pipe diameter is the superior choice in comparison to increased wall strength. Play with bending stress calculators and you'll soon discover this truth. Standard structural pipes of greater diameter are readily available almost everywhere, and are often galvanized for the pipe sizes hams would choose for masts.
  • Butting: This is a material technique to increase wall thickness where the bending moment is greatest. Butted steel tubing has been used for high-performance bicycle frames for a very long time. The special tooling makes these tubes very expensive. You can often nest the next smaller IPS pipe in a Schedule 40 pipe. For example a 2" IPS pipe (2.375" OD) slides inside a 2.5" pipe (2.875" OD; 2.469" ID) with a small gap. Dave Leeson W6NL discusses using aluminum pipes this way for antenna booms in this book Physical Design of Yagis Antennas. Since the increase in bending moment is linear the butt pipe or tube only needs to be long enough to the position on the mast where the bending moment is survivable. Unfortunately, my 2.5" pipe has 0.25" walls and I cannot slide a 2.375" OD pipe inside it. This is where you discover one difference between pipes and tubes: pipes have a seam, and that seam is not ground down on the inner surface. You can see an example of this in the earlier picture of the mated masts.
  • Antenna change: The last resort is to go with smaller antennas or lower them on the mast until the wind and ice survival objective is met. Many hams are loathe to do this even when the on-air performance difference is small.
Do whichever works for you, but be sure you do it. On the other hand, over-engineering is not only wasteful it can lead you into temptation. Putting up antennas that the mast can handle but the tower cannot is a recipe for a very ugly outcome.

A lesson

Many years ago I help to remove a tower and antenna system where the tower twisted in the wind and broke. Only the over-strength mast held it and the antennas together, preventing a ton of steel and aluminum from striking the close-packed suburban houses below! Removal required a very large crane and running interference with the extremely unhappy municipal authorities. My job was to climb the broken tower and rig the attachment between the tower and the business end of a 125' boom on a 25 tone crane.

Trust me, you never want to be in this situation. Out in a hay field a tower or mast failure may be only an expensive lesson. For most hams who live in urban and suburban settings it can be a disaster far beyond your capacity to deal with and get over.

Sunday, November 5, 2017

Patience is a Virtue

I spent part of the weekend in the ARRL Sweepstakes contest. A serious effort was not in the cards since I not only have little in the way of antennas for the moment, the contest itself has become as exciting as watching paint dry. That's a shame since back in the 1970s this contest was the focus of my contest season, since as a VE4 with a small station I lived in a DX black hole and in Sweepstakes I had an easy shot at the US eastern seaboard where my section was often in demand.

The weather was quite bad this weekend so I had an incentive to spend time in the shack, no matter my antenna situation or the antenna work waiting to be done. Rather than the contest my excitement on the bands was chasing DXpeditions. On that front I had success, working VK9CZ on 40 meters, VK9MA on 3 bands, and putting a few other DXpeditions in the log. That was fun.

My first QSO with VK9MA was very nearly scrubbed because of my impatience. Impatience drives a lot of the bad operating in pile ups, whether due to mistakes or calling out of turn. The result of my impatience was in a way humourous, as you'll see.

I had a good shot to VK9MA despite a modest yagi and no amplifier. Late afternoon the long path to VK (via Africa) on 20 meters can be quite good from eastern North America. They were pretty loud and the pile up wasn't unbearably deep or wide. The operator was turning over contacts as a steady clip, though not as fast as the best DXpedition operators.

Thus there were fewer opportunities to call, triggering my impatience. I barely listened between sending my call again and again. His pattern was predictable so that I (and everyone else) could figure out where he was listening with good accuracy. I didn't want to wait around so I tried to make every call count.

But I was too fast on the trigger. Often while calling I would stop to spin the VFO to find a quieter frequency to try my luck. This can be a good strategy. Unfortunately it can also backfire.

Spinning the VFO after a few rapid calls with no response from the DX I was horrified to hear him sending my call. Yes, horrified. Think about what I just did: I spun the VFO! Because of my impatience I was no longer on the frequency where he heard me. What to do?

Luckily I have good short term memory, a valuable attribute for a contester. I thought a moment to develop in my mind a picture of the numbers on the display when I called. He called me a second time. Desperately spinning the VFO I sent my call, hoping the frequency was close enough for him to hear me. A third time he sent my call and a report. I responded with my call again and this time added "5nn tu". With a "tu" in return the pile up resumed.

Was the "tu" merely a polite way of signalling he was giving up or did he really copy me? Luckily I showed up in their online log a few hours later when they started uploading to Club Log.

Of course it is very likely that even had I failed I would work them on that band again soon enough with their good signal and the many days left in the DXpedition. I could only laugh at myself and my poor discipline leading to unnecessary impatience. Patience truly is a virtue. Remember that should you, too, spend too much time calling and not listening in the next pile up. You'll likely get through faster with just a little patience.