For Future Consideration: Tower

Once again I am adding another chapter onto this series about actions I have taken towards my next, and bigger, station. All that Heliax now has a tower to attached to.

This past weekend was a busy one for me. It involved renting a large truck, driving over 1,100 km, picking up loads in two distant locales, then unloading and storing the truck contents on my property. In all, the weight of everything was somewhat over 2,500 lb (1,200 kg). Now I have a large tower, and much more.

The tower you see in the photo has 15 sections, each 10' high, including one base section. With overlap for section splices this tower would stand 144' (44 meters), plus around 15' (4 meters) of mast topped with a yagi.

The assembly resting atop the base section is a prop pitch motor fitted to a platform that mounts to the side of the tower. More about that in future. Just outside the picture frame is a large quantity of guying material, pipe and tubing. Most of the guys will be stripped for the usable parts, with most of the guy wire to be discarded; due to its past service it is necessary to purchase new guy wire for this tower.

Background

This tower was manufactured by Leblanc & Royle (L&R), probably in the 1980s. L&R was in the business of designing, manufacturing, installing and maintaining tower systems for broadcast, military and other applications in Canada for many years. Many commercial towers across the country were once L&R, and many remain in service. While I don't know the details they were likely the victim of a changing industry, failing to successfully transition from previous tower applications to cellular communications. The tower requirements are quite different.

Used and surplus L&R tower can be found in many of the larger amateur radio stations in Canada. The tower I purchased comes from two other VE3 stations. The tower is used though appears to be in excellent condition. Most sections are painted in the familiar white and red colours for aircraft safet, while a few are bare galvanized.

One strong attraction of this tower to me is the many attachments that had been customized for amateur use. These include brackets for the (above) prop pitch motor for rotation of a heavy duty mast and side-mount yagis. These should not be overlooked since they will save me a substantial amount of time and money for design and custom manufacture. However, having seen long service, some maintenance is needed for the custom bearing assemblies and other components. This is something I will look at this winter, now that I have it close at hand.

LR20 specifications

Per the specification at right, my tower is "light duty" LR20 (the numerals are the face width in inches). It is conservatively rated and can comfortably handle ice and wind load when 150' high and holding several long boom HF yagis. Strict adherence to engineering guidelines for guying and loading is mandatory.

One thing that distinguishes this tower from a tower with round legs and diagonals is wind load. A tower has a substantial surface on which the wind acts, a load that the tower must support even without the additional load due to antennas. The engineering specs take this into account. Always always always follow the manufacturer's instructions for tower assembly, guys, anchors, base and load placement.

There are two girts per section, used for guy attachment, bearing plates, side mounted antennas and other loads. Guy yokes (custom U-bolts) are already attached to the girts on my tower that were previously used as guy stations. Depending on my final design I may need to move these.

This tower has a pier pin base, where the base plate is positioned over a 1" steel pin protruding from the reinforced concrete base. This is a common design element in large guyed tower to mitigate the stress on the tower caused by the torque of wind load on large antennas and bending in high winds. By allowing the tower base a limited amount of motion, the guys can absorb these dynamic loads. You can see an example for Rohn tower on W8JI's web site.

Also of note for those of us who do climb is that there are horizontal struts at ~18" intervals on one side of each section. That is a great convenience for climbing and working at height. The girts alone are inadequate since they are 5' apart. Ask anyone who has worked on, say, a Trylon Titan tower what they think of diagonal struts. It is of course important that the tower be built so that the horizontals are all on the same side. I prefer mine on the side that faces approximately southwest to keep the sun out of my eyes and the prevailing wind at my back.

A tower is not a toy

Do not be misled by any sense I might have unintentionally given that this tower is a plaything. Hams use towers to get the best from our antennas, just as we might use a kilowatt amplifier. Both can easily kill you. The only difference between falling off a 150' tower versus a 50' tower is the amount of time you have to think about it on the way down.

Safety is mandatory in the air and on the ground when working on any tower, and especially one of this size. Things always go wrong. It is our job to ensure accidents that do happen are not fatal to people or property.

The weight of the tower sections requires mechanical assistance. Do not rely on the muscles of two or more people. The risk is too high. Better to have one expert on site than a large crew of eager but inexperienced hams. This is not the place to trade safety to save money. Accept the fact that a tower this size is going to incur a substantial expense.

There are several options to put up a large tower. Use the one that works best for you, and that can be done safely and within budget.

• Gin pole - This is the cheapest solution but expensive in time and potential safety events. The pole and attachments must be up to the task of lifting and manoeuvering heavy awkward weights. A tractor or similar device can provide the muscle with a suitable pulley system to minimize gin pole stress and permit horizontal pulling. Winches have been used but are not ideal due to the amount of cable required and the risk of slippage. Steel temporary guys are required before reaching the first permanent guy station, and even higher to reduce sway during construction.
• Crane - The tower can be built on the ground and lifted all at once. A large crew is required on the ground to place the tower onto the base, plumb the tower and especially to secure and tension 12 or more guy wires. If any splice bolts slip the tower sections (typically near the centre of the span) will need to be redone once lifted but before the guys are fully tensioned. The crane will not be cheap, and you want a crane operator and ground crew who are sensible, experienced and safety conscious. If the crane boom is tall enough you can also include mast, rotator and even an antenna or two. The latter requires a second crane or a boom to mast clamp that permits 90° rotation.
• Helicopter - This is similar to erection with a crane but far more expensive and should only be performed by professionals.
• Hybrid - Use a small crane to lift part of the tower, to at least just above the first guy station. Splice slippage is kept to a minimum and only 3 or 6 guys need to be handled. The rest is done with a gin pole.

I have been involved in tower erections using the first and fourth methods. One of those was for an L&R tower of similar height to mine. While this gives me valuable experience it does not qualify me as an expert.

Before it goes up...

There is much to be done before my newly acquired tower goes up. One obvious need is the purchase of a large plot of land; this tower requires almost 1 acre of land, and more with mandatory setback from property lines. I must also perform ordinary maintenance on the tower sections to repair any minor flaws. All tower sections and guy yokes have passed my preliminary inspection. Always inspect tower sections, whether new or used. Inspection is easier on a tower with open steel members than it is on tower with tubular steel legs such as Rohn.

Mechanical work includes bearing repair and replacement, of which there are several: top plate and thrust bearings for the mast and beneath the drive bearing. The prop pitch motor may require maintenance and does require some work on the chain drive system. The motor itself works fine. The homebrew control electronics and positioning system may require an overhaul.

Guying hardware must be inspected and replaced where necessary. The tower came with a large quantity of turnbuckles, thimbles, guy grips, insulators and guy wire, mostly used but some new, in both ¼" and 5/16" sizes. I expect to discard most of the guy wire since its remaining service life is inadequate to my needs. The old guy wire that is in good condition may be used in other projects with less critical requirements.

From here on this is a winter project which I can temporarily set aside. I will now return to my fall antenna work. The 80 meter vertical is next on my schedule. CQ WW is fast approaching.

For Future Consideration: Transmission Line

This is the second in what may become a series of articles about my preparation for a larger antenna farm, perhaps as soon as 2016. The first article was about my acquisition of a 2-element 40 meter yagi (XM240). This one is about transmission lines. That is, low loss coaxial cable.

The problem

In most HF stations the quality of the coax from shack to antennas is often more about robustness, power handling and weatherproofing. Loss on the HF bands for runs under 100' (30 meters) is usually low for RG-213 (or equivalent) coax, and it will handle a kilowatt if the SWRis modest. For example, a 50' (15 meters) tall tower and tri-bander with 75' of RG-213 has a matched loss of less than -0.9 db at 28 MHz. With an SWR of 2 the total loss can be as low as -1 db. Loss progressively declines on lower bands.

In a large station transmission line loss is often a concern. Consider a 100' (30 meters) tower that (for peace of mind) is a similar distance from the house. With additional cable at the top of the tower and into the shack we are looking at 250' (75 meters) of coax. At 28 MHz the matched loss of RG-213 is now -2.9 db and at least -3.3 db with an SWR of 2. Upgrade to a 150' (45 meters) tower under the same scenario and losses increase to -4.0 and -4.4 db, for an SWR of 1 and 2, respectively.

Of course the situation is less dire at lower frequencies. RG-213 can prove adequate at 7 MHz and lower even for these long runs. But for the hams that build these large stations every decibel counts, since it can make a difference in contest results. This is due to impacts on transmit (getting heard) and receive (copying the weak stations attracted by the big signal). There are other matters to be considered, such as whether the coax can be buried, moisture wicking by a braided outer conductor, UV resistance and more. This is why many hams eschew RG-213 and similar coax, since quality is often questionable. They instead use brand name cables in the same size such as Times Microwave LMR-400.

Better coax can be had, if one is willing to buy new or one is able to scrounge. The former takes money and the latter takes time and effort. I favour the latter, if at all possible. Time is on my side since I will not need more transmission line until at least 2016.

Andrew Heliax

When I built my modest station in 1985 I was fortunate to purchase new hardline at a bargain price. This was 400' of Andrew Heliax LDF4-50A, ½" 50 Ω coax. Even at the low per-foot price I paid it was still a goodly sum of money. I was fortunate to acquire new connectors at wholesale price through a friend in the business since connectors can be very expensive. Divided into 3 lengths of 130' this was still a substantial expense for a set of transmission lines from the shack to the top of the tower.

400' of LDF4-50A hibernating in the garage.

The runs were 130' (40 meters) because the tower was 19 meters high and a similar distance from the tower to the shack. Cables were buried for part of the distance. The antennas atop that tower were yagis for 20-15-10 (Hy-Gain TH6DXX), 6 (Cushcraft A50-6) and 2 (Cushcraft 32-19). RG-213 was used for 40 and 80, which I purchased new in bulk, on the spool. It is these same 130' lengths of RG-213 I am currently using in my station today, after having been in storage for over 20 years. There is still 100' or more on that original spool. The rest went to friends who participating in the bulk purchase.

The LDF4-50A has also been in storage. Heliax is very robust, suitable for direct burial, reasonably immune to moisture wicking, and will support its own weight when hanging from the tower top and (if the tales I've heard are true) survive being run over by motor vehicles. Loss is substantially better than RG-213 despite not being much thicker. At 28 MHz the matched loss is -0.35 db per 100' (30 meters). For the 150' tower mentioned above, the loss over 350' is -1.25 db. That isn't bad but, as we'll see, we can do better.

Buying hardline

When buying Heliax one decision is whether to buy new or used. As with anything purchased used it is a good idea to test first, if at all possible. In the case of coax you want to do a frequency sweep of unloaded cable to ensure it is close to spec for loss and impedance. I've heard of hams who carry a VNA to flea markets for this very purpose. Some old or new but rejected cable may show impedance anomalies above 1 GHz, but be perfectly good at HF, VHF and even UHF.

Used cable often has the advantage of having one or even both connectors attached. With the high price of connectors this can be an advantage. With care the connectors can be removed and reused, and the cable cut (if necessary) to the needed length. Shorter lengths can be connected to make a longer run, provided that splices are not buried. Splices must be waterproofed and use the correct connectors.

There is a commonly-heard myth that connectors are lossy and must be avoided for best performance. This isn't true at HF, and not true at VHF and UHF is constant impedance connectors are used (e.g. N). The trade-off is the whether the price of the hardline is low enough to justify buying connectors. They are often hard to find the used market, and are rarely inexpensive.

As we should expect bigger coax has a bigger price. This is where scrounging comes in particularly handy. However, the situation is far from hopeless. Back in 2007 Andrew stopped producing LDF cable, replacing it with the improved AVA line of products. More LDF began finding its way onto the surplus market at attractive prices while the commercial world made the switch to AVA.

If you do scrounge you will find that surplus new LDF4-50A and even LDF5-50A often costs little more than new LMR-400. But, as I said, scrounging takes time. When the opportunity appears you have to act, since you don't know when or if another deal will come your way. Be especially acquisitive of connectors should they be offered at a good price. If you don't need them you can always sell the surplus to your friends. You'll put a smile on their faces, and probably have a ready crew for your next tower project!

Bigger is better

Back in 1985 there were hams who found it funny that I'd run Heliax on HF. For short runs, they had a point. However, the specs of the no-name coax most of them used was not to be trusted. At least I knew what performance I was getting, and that the coax would hold those specs for a very long time even when exposed to the weather or buried.

Hardline specs in TLW do not exactly match Heliax

But that's for short runs. For longer runs at competitive HF stations (or short runs on VHF and UHF) bigger cable than LDF4-50A is desirable. The most common choice is the next step up in size: LDF5-50A. This coax is ⅞" in diameter, with a proportional improvement in loss and power handling. At 28 MHz a 100' length has a matched loss of -0.2 db, or half the loss of ½" Heliax as expressed in decibels. Loss over exceptionally long runs can be better than -1 db up through 10 meters, and even 6 meters.

Specs for LDF and AVA are easily found on the internet. You can also use N6BV's TLW application to approximate loss performance for Heliax. LDF7 and AVA are not in the menu so you'd have to make those a user-defined cable type. TLW is packaged with recent editions of the ARRL Antenna Book.

Going all in

This series of articles titled "For Future Consideration" is about actions I've taken to prepare for my future station. The foregoing discussion is just a lead-in to the latest step I've taken. Sometimes when you least expect it the used market tosses exactly what you need into your path. You have only to pull out your wallet when opportunity knocks. This is what I've done.

Luckily my one-car garage is fairly deep, allowing room for storage. That space has been filled over the years with lots of stuff that I should have sold or thrown out years ago. This I have now done to make space for my newest arrivals.

In the photos at right you can see that I am planning for some long runs of low-loss transmission line to multiple antennas on tall towers. The 400' of LDF4 is dwarfed by the new rolls of Heliax piled up against it. Most of it is LDF5-50A, both new and used. Connectors are either attached to the used lengths or new in the box. These are a mix of N and 7-16 DIN connectors, and at least one UHF connector.

The new LDF5-50A is on the original wooden spool. It weighs a lot. Two of us were needed to roll it up the steep incline of my driveway. Since the photos were taken most of the separate rolls have been placed atop the spool to conserve space and to protect them from wintertime saltwater contamination.

There are also several short runs of cable (<10 meters each) that are suited for stacking harnesses and house entry. Or I can cannibalize them for the connectors.

As additional eye candy there is a roll of LDF7-50A, which is 1-⅝" diameter. The matched loss on this cable is virtually nil on HF (-0.1 db/100' at 28 MHz). Is this size of cable really necessary? Perhaps not on HF, unless the towers are 100 or more meters from the shack, but I do have some interest in returning to VHF DXing. Some contest super-stations use this product on the upper HF bands.

To give an idea of how large this cable is the adjacent selfie photo shows me holding a DIN connector for LDF7-50A next to the coax roll. Putting connectors on large Heliax requires some large tools and care but is not much more challenging than attaching connectors to more ordinary varieties of braided coax. There is no soldering to be done, and the large size eases handling.

Do you really need hardline?

Only you can decide. How much is 1 db worth to you? Or 3 db, the equivalent of stacked yagis? At HF the low loss of hardline is not needed for receive since reception is noise limited. The situation is quite different on VHF and UHF, and even 10 meters, unless you use a remotely switchable low-noise amplifier (LNA).

Transmit is another matter. Country regulations and award programs, including contest categories, almost always specify power at the transmitter. This is as true for QRP as it is for QRO, although the motivations may differ: protect what little QRP power you have, or emit the strongest, legal QRO signal. For everyday use it is often more convenient to use an amplifier to overcome transmission line loss. That is, if you are not already at the legal limit.

Low loss can give you the flexibility to locate your tower and antennas further away, to reduce noise pickup and interactions with buildings and other antennas, and perhaps allow use of a better area (a small hill?) for construction, maintenance and radial field. Although this wouldn't apply in a typical urban or suburban lot, many hams move to rural locations to fulfill their radio ambitions.

I did the arithmetic for what I want to achieve with my future antenna farm. Purchasing an abundance of Heliax was the right decision, for me.

Matched loss versus SWR loss

One final note on the limits of low-loss transmission line. This is as true for open-wire line as it is for coax, even if some books say otherwise. To give an example I'll draw your attention to an article I wrote some time ago, regarding the practical limit of solving antenna mismatches (high SWR) with a tuner in the shack.

In that article I discussed the challenge of attempting to use antennas for higher bands on 80 meters. My choices at the time were an inverted vee for 30 through 10 meters and a 40 meter delta loop. The SWR in both cases is exceptionally high due to the low radiation resistance. The feed point impedance at 3.6 MHz of the inverted vee was 3 - j1000 Ω, and of the delta loop was 0.5 - j80 Ω.

The matched loss of 130' of RG-213 is -0.5 db on 80 meters. For the inverted vee and delta loop on 80 meters the total losses are -25.6 and -13.8 db, respectively. For the same length of LDF5-50A the total losses would be -17.6 and -6.2, respectively. These are better but still far too large.

The lesson is that when using coax with a very low matched loss, correcting a high SWR with a tuner in the shack remains a poor choice. It is almost always better to correct the mismatch in the antenna design or with a matching network at the feed point. Tuners don't solve all ills, and neither does Heliax.

Sleep, Interrupted

Shortly before dawn this morning the smoke alarm sounded for a couple of seconds. It's almost impossible to sleep through, just as designed. Suddenly awake, I guessed it was a false alarm, probably due to a mains power glitch. But I couldn't be sure. The lack of smoke was no assurance since there are 3 alarms, one on each floor of the house, and they're wired together so that if one triggers they all sound.

Fighting off the temptation to go back to sleep I took the prudent step of walking through the house in  the pre-dawn quiet to confirm nothing was amiss. Once I reached the basement I was fully awake and could not resist the lure of the shack. Although conditions were poor due to a geomagnetic disturbance there is still the possibility of DX toward the Pacific, including the low bands. Northward paths were heavily attenuated, which I discovered while playing in the Scandinavia Activity Contest.

Very disturbed conditions confirmed by the high K-index, as posted at WM7D's site

First I just had to check propagation toward northern Europe. I expected little and I heard nothing. It was daylight in Europe so the low bands would be closed in any case, and solar flux was too low to open the high bands until after sunrise. So I tuned around 40 meters even though the DX cluster network didn't display anything of interest.

I came across a strong signal operating DXpedition style near 7.015 MHz. I could just barely make out some distorted backscatter signals up 1 to 2 kHz, confirming this was a split operation. A couple of QSOs later he signed his call: E6GG, the current multi-station DXpedition on Niue. Two QSOs later I was in the log. I then spotted him, which seemed to grow the pile-up quite quickly.

Continuing to tune around I found FK8CE coming through. I kept tuning since I'd already worked him on 40 meters, only pausing to spot him. Flipping down to 80 meters CW I found a pile-up on E6GG. Since it was still 20 minutes before sunrise, with my poor antenna I heard nothing. However it was nice for a change to hear the band so quiet; all the neighbourhood lights and appliances were switched off at that early hour.

Not willing to wait for the sunrise enhancement of 80 meters propagation I shut down and headed upstairs and back to bed. I was soon asleep, happy that another band country was in the log. It just goes to show that if you get on at the right time there is interesting stuff to work even through dreadful conditions.

FT-1000 MP Mark V Field: Mods for IMD and Key Clicks

There is a long tradition in ham radio of making modifications to commercial equipment to add features or improve performance. It is often viewed as worth the risk of (potentially) lowering resale value if those mods mar the equipment or deter buyers that want a "pure" unit, for the increased utility or mere pleasure of it. Since there are few of us who can design or build a modern transceiver from scratch, it also can be an opportunity to place our personal stamp on  the equipment, if only to show we can do it.

Unfortunately it is also true in too many cases that equipment is sold with fundamental design flaws. There is no incentive for the manufacturer to act when the market doesn't react. That is, if sales proceed according to plan and customers are not complaining, why take on the expense of recalls and factory mods? The truth is that few hams will notice or care.

In the case of the FT-1000 MP Mark V Field I purchased last winter there are two particularly nasty problems: key clicks and excess IMD (inter-modulation distortion). Yaesu did eventually fix the key clicks issue in late models (about 8 years after the rig was brought to market) and never did deal with the IMD problem. It isn't as if Yaesu didn't know about the problems. They appear to have chosen to ignore them.

Lucky for us that there are so bright lights within the ham community who care about these issues, and have the technical ability to find and solve these problems. Those of us eager to transmit clean signals and have receivers up to the demands of the toughest QRM during contests and DXpeditions are thankful these people exist. In this case we can thank Tom Rauch, W8JI. His intensive effort to solve the problems of this otherwise excellent rig are appreciated by many.

Many however neither know nor care. If you don't believe me just listen on the bands. When someone in a CW QSO reports they are using an FT-1000 MP all you need do is tune to either side of their signal. Every time I've done this there were key clicks. For the stronger signals these extended several kHz from their centre frequency. This is not good.

Dime versus 220 Ω SMD resistor from the IF board

Danger lies ahead

Assuming you are like me, and you want to benefit from the solutions W8JI and others provide us, it is not always clear sailing. Sometimes the difficulty of successfully executing the mods is understated. Modern electronics is full of tiny SMD (surface mount devices), masses of cable harnesses and connectors and tightly fit boards and enclosures that make access and interconnection quite challenging.

Some of the challenges with which I am most familiar include:

• Eyesight: My vision is no longer perfect as it was in my youth. This is true for many of us. Component miniaturization makes it difficult to see well enough to avoid disastrous results. My case isn't helped by the out-of-date eyeglass prescription I am currently using. A hand held magnifying glass helps or, better, a magnifying plate with its own stand to keep both hands free.
• Soldering: Temperature control and tip selection on our irons is important to proper removal and attachment of circuit board components. The risks are solder bridges, lifted traces and even damaged solid state devices. With an ordinary iron you'll need to be especially careful to avoid damage.
• Wiring harnesses: Tightly bundled wiring harness and the connectors they plug into must often be moved or disconnected for the required access. Labelling or a pre-disassembly photograph are helpful during reassembly.
• Fitting: Modified boards must withstand re-installation without component leads touching chassis metal or other exposed components, and not pinching or disturbing fragile wiring harnesses and connectors.
• Lost hardware: We all drop screws and retention clips, and even SMD components. They're small and our hands are big. Use magnetic tool tips and angle the equipment so that dropped hardware doesn't slide to where it cannot be readily retrieved and can cause damage when power is turned on.

The following is my story of making the W8JI key clicks and IMD mods for the FT-1000 MP. Things did go wrong. I will at least tell you now that in the end I was successful. Perhaps you can learn something from my experience. You should refer to the W8JI article for the reasons and details about the mods.

Interestingly I started this mod in late July. I put it aside until late August when conditions were rotten and I had a few spare hours, finally completing it a few days before publishing this article. For 6 weeks the rig sat uncovered in the shack with wires poking out the side. When the mood would strike me I'd move it to the workbench and continue. This approach may seem odd, but then I don't operate much during the summer so there was no need to rush.

RF board connection for the key clicks mod

This is the most difficult step of the mod because of the difficulty accessing the underside of the RF board. The board is under the fan and power amplifier, and it is encumbered with almost solid, thick wire harnesses with connectors galore. Many of these must be removed before the board can be flipped over.

What I soon determined was that I had two distinct strategies to flip the RF board. But before I describe them, I want to draw your attention to the above photograph of the area (taken after the mod was complete). Compare it to the picture on W8JI's mod page. There is an important difference.

My variant of the FT-1000 MP is the Mark V Field. It does away with the external high-voltage DC power supply, replacing it with an internal AC supply (or operation from an external 13.8 VDC supply) and a power reduction to 100 watts. The metal enclosure to the right of the RF board is the power supply. Other versions of the rig don't have this internal power supply.

The AC supply boxes in the RF board. The board must be slid toward the supply so that the connectors protruding out the rear of the chassis don't impede lifting of the board. With these constraints there is little room to manoeuver the board, requiring more wire harnesses to be moved out of the way. So now we come to my options:

1. Disconnect a large number of the connectors so that the wire harnesses can be pushed out of the way.
2. Disconnect a smaller number of connectors but sever several of the plastic cable ties that bundle up multiple wires.

The first option requires taking copious notes and photos, and great care to avoid damaging wires and connectors. The second option is quicker and less complex but requires care in the re-bundling of the wires to avoid stressing wire terminations and to properly route and seat the bundles. The latter item is necessary or the fan unit will not seat properly or risks catching a wire with the fan blades, all due to the tight packing imposed by the power supply. (Of note, the fan in the Mark V Field has a higher duty cycle, even when only receiving, due to the heat produced by the power supply.)

I chose the second option, though I can't say whether that was truly the best. Be thankful if you do not have the Field version when you undertake this mod. The soldering, routing and testing of the one wire for the mod was comparatively trivial.

Soldering the wire to the underside of the RF board was the simplest step in this part of the mod. The adjacent blurry photo shows the care required to avoid solder bridges. The photo is actually of the IF board wire, but the idea is the same.

IMD mod on the IF board

This is perhaps the easier of the two mods. All one has to do is: turn over the IF board, remove an SMD resistor and solder in a new resistor. While the board is exposed a wire for the key clicks mod must be attached, which will be used later.

The IF board is easy to get to. It's on the bottom of the chassis and only requires the removal of 6 screws and unplugging a few multi-pin ribbon cables. Everything else can be easily moved out of the way as the board is lifted and turned to expose the bottom side. I used needle nose pliers to safely lift the screws, with the Phillips screwdriver still holding down the screw to keep it from slipping away. Some care is needed to unplug the ribbon cables so that they are not kinked or subsequently tangled when the board is lifted.

So much for the easy part. The 220 Ω resistor (R2046) should be removed with solder wick or similar device since there is no easy way to lift the SMD component from the board when the solder on one side is heated. I couldn't find my roll of solder wick (it's hiding somewhere!) so I moved the iron quickly between sides of the resistor until it slid off the board. As we'll see, this may have been a poor choice of technique.

My first attempt to solder in the new 220 Ω resistor did not go well. I got too much solder on the lead to the old SMD tab which was then difficult to remove. Holding the lead down onto the tab while I soldered overheated the tab and it lifted from the board. You can see the ugly result above. The other end solders onto the junction between R2049 and Q2016. The resistor end of the foil trace is the safest place to make the connection since it is easier to access and there is no risk of overheating the transistor. Again, I made a mess.

When I was done I slid a short length of tape under the resistor to prevent the leads from accidentally touching any other exposed conductors. I then remounted the board, applied power and confirmed that the radio still worked. However all was not well. When moved back into the shack I discovered that while it received fine the noise blanker didn't work.

The next day I took it all apart again and checked my work. The resistor lead to the old resistor pad had separated. After checking with an ohmmeter that there were no other obvious problems I resoldered the resistor to the pad and made sure it was secure and had continuity. This time when I tested the rig the noise blanker worked.

Key clicks mod on the IF board

With the IF board back in place it was relatively straight-forward to add the circuitry for the key clicks mod. The only important decision is how to mount the circuit, so that is stable and at no risk of contacting the chassis or other components. Happily there is enough room to entertain options.

I chose to use a spade lug as the principle support. The lug also serves as the ground connection, by being secured to one of the screws holding the IF board to the chassis. Bits of black electrical tape prevent unwanted contact between components, wires, circuit board and chassis. W8JI suggests using a small terminal strip, which I could not quickly locate in my junk box. On his web page he shows another way, with the whole assembly freely floating and encased in heat shrink tubing.

The schematic on W8JI's web page does not label the components, and shows variable resistors which allow tuning the circuit for best key clicks suppression (adjustment of waveform ramps). For my own use I hand drew a labelled schematic.

As simple as this mod is, I still managed to make a wiring error. I discovered the error while testing the mod. Using a second receiver I confirmed that key clicks were reduced, but there was some key-down hash and key-up residual carrier energy. Checking my work I discovered I'd connected the IF board wire (top of schematic) to R2 instead of R1.

After correcting the error I was pleased to see that the mod worked as expected. I then replaced the lower half of the chassis. The top was left uncovered until I decided whether to retie the cable harnesses passing between the fan and the RF board.

Results

I don't yet know if the IMD is improved since that will require a more comprehensive test. I do know from recent contests and DXpeditions that I could elicit audible IMD products within a few kHz of exceptionally strong stations and, one time, in a pile up of American stations calling K1N on Navassa Island.

The receiver testing by Sherwood Engineering shows this rig not measuring up to the best with regard to IMD. However I don't know if this is with W8JI's mod. He claims narrow spacing IMD improvement by at least 10 db, and perhaps as high as 20 db. If true that would put this receiver closer to the best. That isn't bad for a 20 year old rig that can be economically purchased on the used market.

Key clicks are far easier to test. No special equipment is desired unless want a precise measurement. Before the mod it was easy to hear key clicks on a second receiver. Use an attenuator and dummy load to ensure that the receiver is not overloaded. I ran full power from the FT-1000 MP into a dummy load -- transmitting a series of dits -- and had no antenna attached to the KX3, on which I listened. The signal strength was over S9 but well within the receiver's dynamic range.

After the mod the audible key clicks almost entirely vanished. As W8JI says, this is not a perfect cure so there will be some residual clicks that a careful measurement will discover. It is however perfectly adequate. I no longer need to feel uncomfortable about using this rig in a CW contest. Don't hook up an unmodified FT-1000 MP to an amplifier or a big antenna until you do this mod! I guarantee that if you don't you will be noticed. Be considerate of others, and protect your reputation.

The one that got away

While I was busy modifying the rig I had the idea of adding something new, for computer-assisted contesting. Quite a few contest and other rig control software support computer keying via a serial COM port. In particular, the RTS and DTR pins of an RS-232 interface. Since these pins are unused on the FT-1000 MP CAT (computer aided transceiver) serial interface I wanted to add the switching circuits for PTT and CW keying onto the same interface.

This turned out to be more difficult than I expected. The DB9 connector on the rear of the chassis, along with the sockets for PTT and CW key, are mounted on circuit boards. That is, they are not chassis-mounted sockets. Adding the circuitry therefore requires lifting and flipping the associated boards to access the points where wires need to be soldered. This would not be easy considering the host of interconnecting cables that would have to be disconnected to accomplish the task. The added wires should also, ideally, have connectors themselves to allow the boards to be more easily removed in future.

I reluctantly decided not to bother. The mod would in any case be of questionable use when operating multiple radios, such as for SO2R contesting. The better and more forward looking approach would be an external keyer such as the USB WinKeyer which is supported by most software and is emulated by some other commercial keyers.

Comments, Feedback and Questions

I have an explanation below regarding why the pace of articles has slowed recently. This is temporary, and mostly for good reasons. What I want to focus on is some administrative detail. As blog readership increases and I have to deal with the peculiarities (absurdities?) of the Blogger platform, this is a good time to make some adjustments.

Getting in touch with me

I am always happy to correspond with readers, whether just to say 'hello' or if you have questions about one of my articles. Either of the following email addresses will work: ve3vn@rac.ca or ve3vn.fn25@gmail.com

Of course you can always leave a comment on the article. But use email when you want a personal response.

Requesting antennas models and more

I do not upload the EZNEC models and other files to general access. I suggest you send me an email with your request. Many have already taken advantage of this offer.

Comment policy

As of today all comments are moderated. I did this so that I can review comments before they are posted. While this can delay their publication for up to a day or two (depending on my availability) it means I was able to remove the spambot challenge for anonymous and uncredentialed commenters.

Blogger has its quirks, of which the comment credential technology is a big one. It is cumbersome and works poorly (or not at all) with some browsers. I am trying to make this easier for you and for me. You can write the most critical comment you like and I will publish it. I will only delete comments that are wildly off topic, abusive, spam or other forms of self promotion.

Feel free to bring to my attention any technical errors. I want to know about my mistakes so I can fix them. However, I'd appreciate that you silently overlook typos and grammatical errors.

Where are all the new articles?

I've been busy. My time has been split between radio activities, summer fun and a host of family and other responsibilities. There are at present several articles partly drafted which will be published once those activities are complete. Some are antenna articles, particularly those on my fall plans for 40 meters and 80 meters. Others are on equipment purchases for my future antenna farm, and changes to my shack equipment.

I foresee quite a few articles showing up over the next couple of months. Right now I am in over my head with things that absolutely must get done before winter, including preparation for the serious start of contest season in October. Recent poor HF conditions have helped to keep me focussed on what's important.

Fall Antenna Plans: 80 Meters

Now that the 80 meter half sloper is reconnected (I had borrowed the coax for the 6 meter yagi over the summer) I am reminded how awful an antenna it really is. This is a good time to consider alternatives since the noisy summer conditions are still prevailing on the low bands, and will continue for a few more weeks.

To summarize, here are the problems I have with my half sloper:

• The antenna has a significant horizontally-polarized component in many directions. Despite the use of the tower as a major component of the antenna it seems that the wire can often dominate the far-field pattern. Much of the antenna's radiation is at high angles, which is not what I want.
• There are substantial ground losses which severely cut into its efficiency. I am comfortable claiming this based on its on-air performance, feed point impedance (presence of series ground loss resistance) and the software model. NEC2 often has been reported to underestimate losses from real ground, yet even so the modelled losses are substantial.
• Antenna bandwidth is modest. It is cut to resonance within the CW segment (3.5 to 3.6 MHz) and does poorly in the SSB segment (3.8 MHz). I've tried the FT-1000 MP's ATU and an external antenna tuner with poor results. I can match the antenna for SSB, but the matching and SWR loss seem quite high. While adjusting feed line length might help, I'd rather have a broadband match.

These are problems whether I am contesting with QRP or DXing with 100 watts on 80 meters. Both have been frustrating. I had higher hopes for the half sloper. In retrospect I feel my initial optimism was misplaced. Now it's time to do something about it.

Options

As I move lower in frequency my options become increasingly constrained by my available supports and property. Just moving a factor of 2, from 40 down to 80 meters, I can pretty much rule out all horizontal antennas. They will either do no better than what I have or will destructively interact with may high band antennas. Interaction is unacceptable since 80, for now at least, is less valuable for QRP contesting and for DXing.

Regardless of the antenna I choose, horizontal or vertical, ground losses must be addressed. The ground directly under all my antenna is poor, not the medium ground I typically use in my models. I model that way to make the results meaningful for most readers of this blog. My lot is backfilled with sand (septic tile bed) over shale. Soil is only 12" (30 cm) deep.

Do not be deceived by advertising for commercial vertical antennas with "no radials" designs and that have elaborate matching networks, or any home-built antenna that does not require radials, such as a delta loop or half sloper. You cannot so easily dismiss ground interactions, and the inevitable loss.

Radials are needed, although I don't want them. There is too much traffic in my backyard to have wire lying on the surface, even if it is worked into the grass and weeds. Burial is out of the question at this QTH since it would tear up the lawn for what is likely to be a brief deployment. A vertical would have to use the tower that is centred in the yard since it is the only location where radials of any kind can be placed.

As I said, my options are limited. Whether I like it or not I have to go vertical and find a way to put down some radials. This is the only way I can hope to improve low-angle radiation and reduce ground loss. Reducing local noise (QRN), which can be quite severe during the evening, is out of the question since I have no space for a directive receive antenna. With QRP that's rarely a problem since I am far more concerned with being heard. A separate, directive receive antenna is of little value for the same reason.

My objectives for the 80 meter antenna:

• Low-angle radiation suitable for DX. I only need enough high-angle radiation to make contest contacts with the nearby US northeast and midwest.
• The minimum radial field to reduce ground loss to an acceptable level.
• Feed system to achieve a 50 Ω match from 3.5 to 3.8 MHz, for the tower, top loaded with a tri-band yagi, and assorted cable runs.

With those points in mind we are ready to proceed.

Resonance

There are so many variables to determining the resonant frequency of a vertical constructed from a tower and yagis that it is often best to just go out and measure it. Unfortunately this requires that the radial system be in place. For a small number and length of radials the radials play a substantial role in determining the resonant frequency. With more and longer (λ/4) radials the radials tend toward non-resonance, leaving the monopole itself as the principal tuning variable.

Calculation can get us close, or at least close enough to guide the design of the radial system and feed network for a tower with a yagi on top. There is a formula for this in the 1st edition of ON4UN's Low-band DXing, page II-32:

L = 0.38f ( H + SQRT( S ( 1000 - H ) / 500 )

L is the electrical length in degrees (λ/4 = 90°), H is the height in feet, S is the area of the yagi in square feet, and f is the frequency in MHz. This formula is not in the 5th edition, having been replaced by a graph for a more restricted range of figures. My guess is that this was done to discourage readers from applying the formula to extreme cases where it is inaccurate. Therefore only use the formula as a rough estimate.

Per this formula, my tower plus mast height of 15 meters, with an Explorer 14 at the top, has an approximate electrical length of 105° at 3.65 MHz. It should therefore be resonant below the band edge. This is close enough to λ/4 to allow a simple matching network. I like that.

However there is more involved in getting a good match on a ground mounted vertical. With a small quantity of radials the radial length contributes to the resonant frequency. With more and longer ones the radial system becomes non-resonant. I will have a few short ones, so it matters.

Ground loss

There are ample resources in the amateur literature about ground loss and the mitigation of ground loss. One in particular I like is the 5th edition of ON4UN's book. On the internet, one good place to look is the series of articles by N6LF. Read them if you have or intend to build a vertically-polarized antenna for the low bands. I will only say a few words here that are specific to my situation on 80 meters.

Z = ( Rrad + Rgnd + Rant ) + jX

The resistance term R in the antenna feed point impedance Z is composed of 3 series resistances:

• Rrad: Radiation resistance
• Rgnd: Ground loss
• Rant: Conductor and ESR (equivalent series resistance) loss in the antenna and matching network

For a typical λ/4 vertical monopole with a perfect ground plane the radiation resistance is 37 Ω. Ground loss due to poor ground or ground plane can be larger than the radiation resistance. Conductor loss is typically negligible for an antenna of this type, however capacitors, inductors, transformers and transmission line stubs in the matching network (especially for short verticals) can also be quite large.

The only way to manage loss outside of the near field (far field ground reflections) is to move to a better QTH! This is outside of my control for the time being, as it is for most hams. What I hope to manage is near field ground loss close to the antenna. This is where the radials come into play.

Using EZNEC, I built a model of a vertical with two grounds.The first ground, out to 8 meters distance from the tower, is poor (0.002, 10) to account for the sand fill and bedrock. From 8 meters outward I use a medium ground (0.005, 13). The intention is to approximate near-field ground losses without distorting the far-field pattern. That's the best I can do, knowing that nearby buildings are within the near field. But then that's true for any low band antenna on my property. There is a significant change in ground loss when the media parameters for that inner ground are varied.

Matching network components should be selected for their low ESR. It is a mistake to only pay attention to the component values and their maximum voltage and current ratings. Transmitting capacitors (fixed or variables) and high-Q coils are best. The loss is there at all power levels so don't take shortcuts if you, like me, operate QRP.

Radial system

The radial system is unlikely have more than 8 radials. Their maximum length is limited by the size of my backyard and fixtures. Toward the south I can go quite long. North toward the house allows lengths up to 15 meters, and shorter where I have the deck and and landscaping. The main limitation is east and west, where the maximum possible length is 7 meters. Although my lot is ¼ acre it is only 15 meters (50') wide.


With this constraint my choices are to go long where I can and short where I cannot, or to choose equal but short lengths for all radials. The question is which does better? Radial asymmetry is something I've dealt with before, its good and bad points. Once again, EZNEC helps to answer this question.

In the view at right (with currents plotted), X is east and Y is north. My lot is 15 meters wide along the X axis. My house is about 15 meters north of the tower. Going south, there is about 25 meters of available space.

In this first model wires #2 and #4 are 7 meters long. The diagonal wires are 10 meters long and wires #3 and #5 are 15 meters long. It turns out this is a poor arrangement.

Most of the radial current is in the 6 longest radials, with almost no current in the 2 short ones. When the current is so low their effectiveness is quite poor. Snipping those two wires from the models had a negligible impact on ground loss (-0.1 db). The azimuth pattern is omni-directional for all reasonable arrangements of 6 or 8 radials. It is just ground loss and resonant frequency that are effected.

When the two longest radials are reduced to 10 meters length the current becomes more equalized and ground loss is slightly reduced. The relative current flowing in the 7 meter long radials is also higher. I decided to proceed through the rest of the modelling with this arrangement.

Antenna feed and matching network

For the typical shunt-fed tower it is necessary to use a gamma or omega match since the tower is not isolated from ground. The combination of electrical continuity into the concrete-embedded tower base comprises a Ufer ground. My tower is isolated from ground, though not in an ideal fashion. The preserved wood base is a poor conductor, even when wet, and its ground contact area is less than 1 square meter.

It may be worth an experiment to feed the tower directly. If the feed point impedance at resonance comes reasonably close to 50 Ω I'll take it as an indication that the tower's ground isolation is acceptable (see below).

To begin the analysis I added a radial system to a vertical monopole in EZNEC. The radial system has 8 radials of 10 meters length, except for the east and west radials which can only be 7 meters long (see discussion above). Since the radials in this configuration affect system resonance, the monopole must be tuned once the radial lengths are set.

The SWR plot above has the monopole adjusted to an electrical length that is resonant at 3.6 MHz.Notice that the feed point impedance is 60 Ω. This is 23 Ω higher than the 37 Ω of a ground-mounted vertical with an ideal (zero loss) radial system. Assuming this reflects reality (which is unlikely) the near field ground loss would be approximately -2 db. This does not include other environmental loss, such as nearby houses and ground reflections beyond the near field. The true ground loss almost certainly will be greater.

Ground loss is undesirable. Yet if it can't be avoided we can at least use it to our advantage. As the cliche goes, when life serves us lemons, make lemonade! Here we find that the ground loss makes it possible to achieve a broadband match to 50 Ω coax without a matching network. This is not unlike some commercial tri-band yagis where the trap loss permits a direct match to 50 Ω coax even though the radiation resistance may be half that value.

All we now must do is add a series capacitor (between the coax centre conductor and the tower) to compensate for the inductive reactance due to the tower's resonance at a lower frequency. The capacitor would be adjusted for minimum SWR at the selected centre frequency of 3.6 MHz. Tuning can be done with a variable capacitor, and then substituting a fixed capacitor of the required value.

Should direct feed result in a higher SWR (due to actual ground loss or excessive ground interaction at the tower base), a gamma match is the next best bet. The estimated requirement is a gamma rod (or wire) about 7 meters long, a series capacitor to tune the gamma match and tying the radial system to the tower base.

In the unlikely event this is insufficient, an omega match would be required. Were I to attempt to shunt feed the tower on 160 meters, an omega match would certainly be required since the electrical length of the tower would only be 53° at 1.85 MHz. The additional capacitor would add loss, though it would be small in comparison to higher ground loss of the small radial system.

Transmission line

In an ideal vertical installation the coax transmission would be buried to minimize antenna coupling, and would have a substantial common mode choke at the base of the vertical. My situation is far from the ideal, and that may be okay. The coax will have to run overhead, in parallel with all my other cables out to the tower, to avoid damage to the cable and to people.

Some amount of coupling and therefore common mode current is going to be unavoidable. Even were I to follow the ideal for this one antenna, there would still be coupling to the several cables running up the tower to the rotator and other antennas. I have that very situation today with the loaded half sloper antenna for 80. There is coupling, though not enough to be a problem. Running a kilowatt would change my opinion, but that won't happen.

In all likelihood I will run the coax overhead, with all the other runs, and have it dip down toward the feed point at the tower base. Since I will be using a 130' (40 meter) length of RG-213 there will be enough spare coax to wind a coaxial choke. That choke must not be "scramble wound" because the inter-turn capacitance would render the choke ineffective. However, I am unconvinced that a properly wound coax choke is worth the trouble because I know there will be coupling back to the shack on the other cables. This decision will be deferred until I build the antenna.

The plan

I'll be removing the half sloper when I am ready to install the second 40 meter inverted vee. I plan to do that in the next two weeks (early September). When that is done, and the septic tank is pumped, I'll be ready to proceed with the 80 meter vertical. Allowing time for experimentation and a further delay toward the end of lawn mowing season, I should have radials in place and the antenna ready by early October.

Elevation pattern of my tower vertical with the ground,
radial system and feed system discussed in this article

One problem I foresee is the ability to confirm performance with a reference antenna. Unfortunately the half sloper cannot be kept as that reference. Using a 40 meter antenna with a tuner is a poor alternative since, in earlier testing with this arrangement, its performance is very poor and therefore unsuitable as a reference. I have no good third alternative.

Based on models alone, it appears I can expect at least 3 db low-angle gain improvement, and probably more, in comparison to the half sloper. Some of that comes from the switch to vertical polarization and the rest from reduction of near-field ground loss by using radials, poor as those radials must be.

I may have to roll up the radials when not in use, at least until early November when people traffic in the yard is no longer a factor. Then it'll be safe until spring thaw.

Once the antenna is built, tuned and I have some performance observations from on-air use I will follow up on this article. You can then compare my modelling alternatives with my final choice of feed and radials.

Fall Antenna Plans: 40 Meters

Fall is rapidly approaching. For me that means preparing the antennas for fall and winter contests, and the occasional DXpedition. Summer has been a down time for my radio activities, with travel, home improvements, sports and other activities. The articles in this blog have been sparse. Now is the time to get serious about antennas.

The 6 meter yagi is now out of the way, making room for other antennas. There is little I can do for the high bands (20 through 10 meters) with my current supports so there will be no changes for those antennas. It is 40 and 80, and possibly 160, where I desperately need improvement. This is especially true if I again enter the QRP category in the major contests. On these bands every decibel counts when others can barely copy me, or not at all.

Final decisions have yet to be made. Options are limited, as are the performance improvements. I'll take you through my thinking at this stage so you'll understand my choices. Later, when the antennas are built and tested, I'll relate how I came to do what I will have done. In this article I'll discuss 40 meters, deferring the other bands to future articles.

Pattern

My only antenna for 40 at present is a multi-band inverted vee at an apex height of 14 meters. One end is tied to the tower and the other to the house eaves. It is asymmetrical, though not by a lot. It is enough to skew the pattern, as you can see in the adjacent plot.

An inverted vee is not really an omnidirectional antenna, even if it is often billed as such. It is only more so than a dipole. You can read how I came to choose this antenna in an article I wrote in 2014.

Notice the azimuth pattern, at a DX optimum elevation angle of 10°. I set up the EZNEC model so that east is to the right. The antenna is replete with compromises.

Europe is down -2 db from where it peaks, as is much of the US. Asia is down -5 db and the southern US, Caribbean and South America are even worse. My operating experience tells me quite clearly this is hurting my contest scores and DX performance. I need a better or a second antenna to fill these gaps.

My best options are as follows, as constrained by my property and supports. There will be no new tower at this QTH this year, and perhaps never.

• Inverted vee: Mounted at the top of the tower this antenna would have the same 14 meter apex height as the multi-band inverted vee. Made symmetric with an interior angle of 90° it would be oriented to be at approximately a right angle to the other inverted vee. In this way interaction with the tri-band yagi on 15 meters above it and the vees would be small. While a tight squeeze I have tie off points selected that would make this work.
• Omega-tuned boom dipole: This involves extending the boom of the Explorer 14 by at least 6 meters and making an omega match with the tap being a wire tied to the end of the existing boom and angled downward to the mast just above the mast bearing. This is a tried and true design that I previously considered but rejected because of the complexity of raising the extended yagi. That remains a task I am loathe to tackle.
• Rotatable dipole: The driven element of my recently-purchased Cushcraft XM240 can be mounted alone on the mast and rotated. It would be mounted parallel to the yagi's boom to avoid interaction, which I've modelled and seen that it is quite severe on 15 meters though acceptable on 20 and 10. At 43' long (13.5 meters) it fits within my 50' wide lot but in windy conditions could tangle with the trees that serve as the tower's guy anchors. Some careful measurement would be required. The wind load is substantial (~3 ft²), so it would have to come down after the winter season, before spring and summer storms arrive.

All of these antennas would have a feed point at the top of the 14 meter tower (DMX-52) that currently supports a Hy-Gain Explorer 14. The RG-213 transmission line is what was used for the 80 meter half sloper and was temporarily used for the 6 meter yagi. That coax is now free since I have other plans for 80.

I modelled the inverted vee and rotatable dipole in EZNEC and overlaid them on the azimuth pattern of the existing inverted vee. All are at an elevation angle of 10°.

First, notice that the inverted vee on the tower has less gain at low angles. This is because the interior angle is smaller than on the multi-band inverted vee. The difference is about -1 db. Due to that and constraints on tie off points, it does only a modest job of filling in those pattern gaps. Northwest and southeast are worst.To the north the improvement is just 2.5 db and to Europe there is no difference. Where the new antenna does well is to the south where it is ~6 db better. This pattern of this inverted vee is more omnidirectional due to its symmetry, a symmetry that might not survive real-world interactions.

As expected the XM240-derived dipole does best, since its average height is higher than the inverted vees. Even with the coil loss (-0.36 db) the dipole gain peaks 0.5 db better than the multi-band inverted vee. (NB: in an earlier article we saw that a dipole typically beats an inverted vee with a 120° interior angle by 1 db.)

The performance improvement comes at the expense of wind load and the need to rotate the dipole to get the most from it. Of course with both antennas online it is possible to switch instantly. At times when both high and low bands are open there is the additional matter of the dipole pointing of the side of the tri-band yagi. But it does allow working the US and points north and south while the yagi is pointed to Europe.

Interaction

The model view at right, with currents, shows the high coupling when the dipole is rotated to where both antennas are in the same plane. It turns out that interactions are a major determining factor as to which antenna I will go with. This can, and does, degrade both antennas' performance.

The nearness of the ends of the dipole and inverted vee is not due to perspective; they are ~3 meters apart (the vee is tied off to the tower). For model simplicity the other elements of the multi-band vee are omitted since their effect is negligible.

To test this out in the EZNEC model I fed each antenna in turn to estimate the effect of interaction. I then rotated the dipole to measure how the interaction changes with direction.

Interactions when the inverted vee and dipole are in the same plane (left) and orthogonal (right), at 10° elevation

When orthogonal there is little interaction. Compare the right pattern with the one at the top of this article. (The vee's pattern is not skewed; it has been rotated in the interaction model.) Low current on the inactive antenna confirms this. When collinear (in the same plane) the impact is large. Antenna lobes are no longer where we want them! However there is a gain effect, as in any parasitic array, with the amplitude of the major lobes 1 to 2 db higher than in the non-interacting (orthogonal) orientation. Unfortunately this gain is not useful or reliable.

The SWR for both antennas in the collinear case are poor. Resonance is shifted and bandwidth is reduced for both antennas. Even if it were possible to live with the pattern distortion, the large swing in SWR is not tenable for most operating, especially contests, and would at least require frequent adjustment with an antenna tuner (preferably automatic).

Where I go from here

This analysis demonstrates the importance of checking interactions between antennas for the same or harmonically-related bands. My antenna decision is heavily constrained by interactions. I could not put up a rotatable dipole unless I remove the 40 meter element from the inverted vee. That is not desirable.

In my earlier interaction modelling I was able to demonstrate modest interaction on 15 meters between the tri-band yagi and the 40 meter inverted vee. Again, worst case was when they were collinear (yagi pointed east). I judged the degradation to be acceptable: about -1 db gain, poorer F/B but little effect on SWR. Compromises are sometimes unavoidable. But you can't make an informed decision until the interactions are tested, in a model (preferred) or in the field. Spending time on this analysis saved me time and effort, and disappointment.

My choices now come down to these options:

• Install the rotatable dipole and remove the 40 meter inverted vee. I would lose instant direction switching and have to do some mechanical work to modify the inverted vee and to install the dipole on the tower. The higher wind load is a risk, though I believe it is managable if I take the dipole down in early spring. But then I would have no 40 meter antenna at all.
• Build and install a second, 40 meter only, inverted vee on the tower, orthogonal to the first. I would retain instant direction switching and avoid destructive interactions. The 90° interior angle of the vee reduces gain but is necessary to avoid degrading the yagi's performance on 15 meters. Installation of this vee presents a mechanical challenge in that one leg has to be tied off at some height on a suitably placed tree. There is a wasp nest in the way (I'm allergic) that I'll have to first remove!

I'll report back on what I decide to do. I may come up with a further option to consider.

A subsequent article I will discuss my options for 80 and 160. I have fewer good options for those bands. I may decide to entirely forgo 160 this season.

6 Meter E-season Wrap-up

Over the past couple of weeks the number and quality of sporadic-E openings has drastically declined. While there may still be a few good ones, for me this marks the end of the 6 meter season. The temporary small yagi I built and installed to get back on 6 has done what I intended.

In this article I will recap my brief return to the "magic band", now that it is coming to a close.

Statistics

First, the numbers.

• Contacts: At least 100, but not counted. Most came in the ARRL VHF contest and the Es peak in late June.
• Grid squares: 75+ worked, with over half already confirmed on LoTW.
• DXCC countries: 11 worked, including Canada and the US. The other 9 ranged from XE to the southwest, several in the Carribean, and several more across the Atlantic Ocean. More countries were heard but not worked.
• Continents: North America, Europe and Asia. South America heard but not worked.

I as satisfied with these numbers even though they are not impressively large. Some have reported the season to be below average. That may be true. Although I have lots of experience on 6 meters from years ago my recollection is fuzzy and my poor antenna tended to make every opening this season a poor one.

It was well worth the effort of putting up an antenna and wasting some nice summer weather closeted in the basement shack.

Antenna performance

Running 150 watts I am pretty well able to work what I can hear. I only wish I heard as much as others. Many DX and marginal openings allowed others in and near my own grid (FN25) to work stations I could not hear at all.

The poor performance I'm experiencing is a combination of a compromised antenna -- nestled close to the tri-band yagi -- living in a river valley, and noise level. There is no easy way to disentangle their respective effects, except to not they all limited my results.

I seem to do well on aurora scatter, mostly done aiming across and along the wide Ottawa River. The yagi is small and so has a wide beam width for scattering off aurora well above the horizon. I only suffered on the longer auroral-E paths to VE6, VE7 and KL7, which is more due to poor antenna gain. Stations in all these call areas were heard during one excellent aurora opening.

The same appears to be true for Europe since the northeast direction is unobstructed. It comes down to a matter of antenna height and gain, of which I have little. I was very happy to work the few Europeans that I could. There were others I either could not hear or could not work.

The big problem is south, looking into the hill I mentioned in an earlier article. XE was not a problem, which skirts the hill by aiming southwest. Caribbean and South America were the toughest DX paths. I was happy to work what I could, and dream of what I might have worked with a better antenna.

Noise

With a proper antenna I am able to hear noise much better than before. This is clearly not good. Getting the noise source off the side of the yagi helps, but that is unfortunately in directions with little to no activity. The is typically in the range of S3 to S7 at SSB bandwidths, and occasionally even louder.

I mostly kept to CW where a narrow filter usually cuts the noise to a managable level. The high CW activity on 6, more so than I remember back in the 1980s, made this strategy a successful one for me.

KX3

I use the Elecraft KX3 on 6 meters since the FT-1000MP is HF only. An outboard amplifier raises my signal from QRP to 150 watts. It can now update my earlier opinions of the KX3, which had focused on HF contests and DXing.

In sum, I am not too impressed with the KX3 on 6 meters. There must be some aspects of the DDS and receiver that are different than on HF. I did not delved deeper to discover the reason for what I observed.

• Tuning artifacts: When the VFO dial is spun there is often a loud ratcheting sound as the DDS makes its frequency steps. It can hide the very signals you wish to hear. Sometimes I had to tune more slowly than I'd like The manual talks about this and suggests how to reduce the effect, but not eliminate it entirely. There are trade-offs. Maybe I'll try it someday as an experiment.
• Single signal reception: In what is largely another tuning artifact, when tuning through the opposite side of zero beat, signals bleed through to the AGC. The effect seems less severe when not turning the VFO. The AGC pumping is worse than I've encountered on any of the HF bands.
• Noise artifacts: When tuned to a reasonably loud signal it can often be heard to crackle (sizzle?). It is more apparent on a continuous tone (CW/carrier) than SSB, but it's there nonetheless.
• Spurious signals: Disconnect the antenna and tune the band and I discovered perhaps a half-dozen spurious signals of significant amplitude between 50.0 and 50.2 MHz. Considering the receiver technology (direct conversion) these are not "birdies", so I label them as spurious. When I connect the antenna there are lots more to be heard, but those are not the fault of the receiver.
• Noise blanker: The dreadful noise I am dealing with can be significantly attenuated by the noise blanker (NB). Unfortunately the NB also reduces signal amplitude and adds substantial distortion. Careful adjustment of the NB level can help, though in most cases I get better results with the NB off.

Despite all the negativity in the above list, the KX3 did the job and I still like it just fine. It isn't the greatest rig around, but then that is not its purpose. For a small, portable, high-performance QRP transceiver it does very well indeed.

Hurry up and wait

Years ago it was tedious work to watch for openings. Often when I was home I would leave the receiver tuned to 50.125 MHz (the domestic calling frequency) with the volume set low. If I heard something I might check it out for a potential opening. There was also WWV for the geomagnetic indices that could herald aurora openings. At the height of the solar cycle high solar flux readings promised real DX.

It's much easier today. DX spotting networks are available with any internet connection, including my smart phone. All I need to do is look for spots on 6 meters and judge whether it's worth going down to the shack.

Even so there is time and effort required for success on 6. Most openings on 6 are marginal: signals are weak and fleeting. If you hear something enticing you have to jump. Wait a few minutes and the opening or wanted station can be gone, and may not come back until next year, or longer. Listening isn't enough: someone has to transmit. Many times I would go down below 50.1 MHz and loop CW CQs with the antenna pointed in a likely direction. Someone will answer, eventually, if sporadic-E has been reported by others in my vicinity.

Other times it's tedious tuning of the VFO, with longer stops at every station or beacon spotted. This is not welcomed by those with busy lives, hams who can only operate when life allows and not when the propagation dictates. Be prepared for that if you venture onto 6 meters. The rewards are many, but then so are the sacrifices.

Next up

Temporary means temporary, so the 6 meter yagi's presence will last only a little longer. I expect that by mid-August the yagi will be taken down and stored in the garage until next year, or perhaps even later. My plans for 2016 are unclear.

The feed line I co-opted has kept me off 80 since early June. This was little sacrifice during the summer's high noise level and low activity on the low bands. The coax will likely be reconnected to the 80 meters antenna for at least a short time. I have plans for improved low band antennas before the contest season arrives. Those plans will be the subject of a future post.

Closer Look at the XM240 LCA

For my recently-purchased Cushcraft XM240 40 meter yagi I speculated on modifying it for improved performance. The primary options are to convert it into a W6NL Moxon or to replace the low-Q coils with high-Q coils. I built an approximate model of the antenna in EZNEC to evaluate the second option.

The coil is part of the LCA (loading coil assembly). The coil is close-wound on a fibreglass form, an attached to short aluminum tubes at each end. The LCA with the protective coating removed can be see on VE6WZ's web site. You may want to keep that page open while you read the rest of this article since I frequently refer to it.

Calculating the Q of a coil is difficult due to the many factors at play. It is typically easier and more accurate to measure it. Most hams, including me, do not own suitable test equipment. VE6WZ used software to estimate the coil Q and ESR (equivalent series resistance). As I said in my previous article that, if correct, the loss is as much as -3 db and coil heating is excessive. As I said there, I doubted these figures. But how to proceed? It is important to know the loss since it will be a key factor in whether or how I modify the antenna before its expected use in 2016.

The inside story

A close-up of one end of the LCA is shown at right. The ¾" fibreglass form fits snugly inside the ⅞" aluminum tubes, attached by what appear to be rivets. A screw electrically bonds the coil wire to the tube.

Some internet searching told me that the loss tangent of fibreglass is heavily dependent on the formulation. At the high end of the range I calculated an ESR of 8 Ω for the coil at 7.1 MHz, which is what VE6WZ calculated. Presumably that is the loss tangent for fibreglass used in K6STI's software calculator. The calculated coil Q is very low. However at the other end of the loss tangent range the ESR would be a very good 1.5 Ω. Calculation alone is clearly inadequate to gain the required insight.

Puzzled by this difficulty I did continued searching. A passing remark on a ham forum gave me the hint I needed. That person called the form a fibreglass tube. A tube is hollow, not solid. K6STI's calculator appear to assume that the form is a solid rod. I picked up an  LCA, pointed it at an open window and held the other end close to my eye. I saw daylight. Now the trail was hot.

It was difficult to be certain how the interior was structured because the light coming from the other end cast dark shadows from several dark protuberances from the tube walls. But the small diameter tube does not easily allow illumination from the same end I'm looking into with my eye. Fortunately my smart phone camera has a small lens and an adjacent LED "flashbulb" . With some care I was able to get both positioned within the tube opening. I pointed the far end  at daylight and took the following unusual photograph.

The flash was so bright within the LCA's confined space that the metal reflections stopped down the automatic exposure to reduce the far-end daylight to black! Despite this the interior structure is clear.

The rivets are obviously metal (presumably aluminum), as evidenced by their reflectivity. The fibreglass form is definitely a tube and (not clear in the picture) has a narrow wall thickness. The self-tapping screw that bonds the coil to the aluminum is very evident. As an aside, this reminded me that I need to replace the screw with a bolt that goes through the other side of tube, which is a well-known design flaw Cushcraft has persistently failed to fix. Due to the perspective of the camera and hardware alignment the rivets and screw at the far end of the tube are hidden behind those in front.

The upshot of this exercise is that the coil does indeed have an air core. The note by VE6WZ that some have measured the coil Q to be 200 is now entirely credible. Since fibreglass fills only a small fraction of the coil's interior volume its contribution to inductance and Q is small. This is good news.

Inductance, Q and loss

Since those unnamed sources and VE6WZ's calculations for an air-core coil of the LCA's dimensions agree on a Q of 200, let's proceed on that assumption. We can now compare an ideal, zero-loss coil (Q=∞), the stock LCA (Q=200) and VE6WZ's high-Q coil (Q=767).

First we need to agree on the inductance value. VE6WZ's measurement is ~15 μH. An air-core coil of the LCA's dimensions give an inductance of 11 μH. This is a difference that must be explained. I think it is fair to conclude that, per his pictured test apparatus, there is ample stray reactance due the long test leads and the attached tubes to account for the difference. There is no need here to speculate on the accuracy of the pictured test device.

I am also swayed by my EZNEC model which only works well when the load is set to about 11 μH. While I cannot use the Leeson correction, I did use an average element diameter that is roughly consistent with a stepped-diameter correction for an XM240 element. Whereas an inductance of 15 μH in the model is wide of the mark, requiring unrealistic element truncation.

For a Q of 200 and X of 500 (11 μH at 7.1 MHz) the ESR is 2.5 Ω (R=X/Q). I then chose a test frequency where the radiation resistance is a little above its minimum near the frequency of maximum gain. Recall that in a 2-element yagi with a reflector parasite the maximum gain ought to be placed at the bottom of the target band for optimum performance across the band. Since I am targetting the CW and DX SSB segments I chose 7.05 MHz.

The resulting gain figures versus ESR for the several LCA options are as follows:

• 0 Ω (ideal, zero loss): 5.71 dbi
• 0.9 Ω (VE6WZ high-Q coils): 5.43 dbi
• 2.5 Ω (estimated stock LCA): 4.94 dbi
• 8 Ω (now-invalidated estimate of stock LCA): 3.43 dbi

F/B differences are negligible. Feed point impedance and SWR curve are only modestly different across the first 3 selections. Relative to 7.05 MHz the gain differences (coild loss) will tend higher toward the lower band edge, and gradually decline with increasing frequency. This is due to the radiation resistance change with frequency.

The high-Q coils do very well, being about -0.3 db from the ideal. Compared to these coils the stock LCA is down a further -0.5 db. That's also very good, and better than I expected.

Conclusion

I am now inclined to stick with the stock LCA. In my judgment an additional 0.5 db is not worth the effort involved nor the damage risk due to the exposed and more fragile high-Q coils. The better alternative is to forgo the coils and do the W6NL Moxon conversion which does away with the coils and coil loss while also improving SWR and F/B performance.

However I still need to replace those self-tapping screws on the LCA with through-tube stainless steel bolts. I don't want a coil failure to occur in the midst of a contest during a frigid northern winter.