The tram line itself was a exercise in choreography since setting it up (and removing it) requires hauling lines up the tower, moving each around the many obstructions on the tower, clearing it over the director end of the large 5-element 20 meter yagi (lower yagi of the stack, fixed on Europe) and attaching it to a winch anchored at the base of the other large tower -- the towers are 200' (60 m) apart.
If everything goes right this can all be done myself. That would be a foolish bet, hence Dave's welcome presence.
There are no pictures of the tram or yagi raising. There are so many articles about trams in this blog that it would be largely superfluous. If you want to learn more, type "tram" into the search box and you will be amply rewarded.
One item that I'll note is that the tram was anchored high on tower, just below the rotatable 5-element 15 meter yagi. That is above the long "false mast" built for this antenna. Once the new yagi was comfortably past the elements of the big 20 meter yagi the tram line was slackened and the haul rope reversed to lower the antenna to the bottom of the false mast.
As noted in the construction article this antenna is very lightweight. One person can easily pull it up the tram line. Most of our time was spent frequently stopping and checking our progress to ensure that nothing would tangle. It is surprisingly difficult to gain a full 3D perspective of the arrangement just by walking around on the ground and looking up.
From long experience I understand the necessity of proceeding in small steps to be certain what's really going on up there. With more ground crew I could have positioned myself on the tower for a better perspective and guide the operation with full confidence.
The picture shows the yagi installed on the bracket and pointing south. The 5-element 20 and 15 meter stacks are pointed northeast (to Europe).
Let's talk about the tower brackets. They secure the two ends of the false mast and were made from metal I had in stock. The tower attachment is unique to the LR20 guyed towers that I have. There are girts approximately every 5' (two per 10' section) for attaching guys or equipment. Other towers have their unique attachment requirements so a detailed discussion won't be too useful to most readers. Similar brackets for my towers have been discussed in detail in previous articles.
The lower bracket bears the weight of the mast and antennas so it must be built accordingly. It is ⅜" × 3" aluminum alloy angle stock. It was obtained free and includes a variety of holes from its original commercial tower application. I've used more of this material for other side mount brackets. I'm happy to have it now that aluminum prices have soared.
An offset vertical load creates significant shear stress on the bracket, tower girt and connecting hardware. While not A325, the ½" grade 5 bolts tying the bracket to the tower girt have an unthreaded shank where they pass through the bracket and girt. Bolts are weaker in shear at the threads. I can stand on the end of the bracket and jump up and down. I did just that and it didn't flex. The upper bracket has no shear load so it can be less bulky. The galvanized angle I selected for it was ideal for the job, but not for dancing.
The brackets were carried up by me and then the mast pulled up with the same rope that was later used to haul the yagi. I did this work myself at the cost of a couple of extra climbs. I don't call in favours for small jobs, leaving that for bigger ones that should never be attempted alone.
The false mast spans 10' to fit another yagi to be fixed south; it's long enough to require 2 pictures. I am considering additional antennas for it but there is no rush. The interaction models are guiding me in this and there is a lot to consider. It is worthy of an article on its own due to the complexity and performance implications. Look for that article before the end of the year.
For now I will mention that there is interaction among the yagis -- the new yagi sandwiched between 5-element 15 and 20 meter yagis -- but that it is quite small and therefore acceptable. The 15 and 20 meter 5-element yagis are negligibly affected by the presence of the new yagi positioned between them.
Notice the stop bolt under the mast. It is the primary path for transferring the vertical load to the bracket and tower. The saddle clamps only need to keep the mast from rotating. This is preferable where it can be accommodated. Without a stop bolt more saddle clamps can be deployed to deal with the vertical shear load; I use 4 better quality saddle clamps on the boom-to-mast clamps of my large yagis. Common saddle clamps (muffler clamps) found in hardware stores are not designed for shear loads so choose your hardware with care.
The dacron rope boom truss is simply tied to a clamp on the false mast. I probably could have forgone the truss entirely since there is very little sag. It is good insurance nevertheless. I didn't get a close up of the 15 meter truss anchor so here's a picture of one on the 3-element 20 meter yagi. A thimble avoids the risk of steel edges cutting the. A copper wire clip ensures that the granny knots can't unravel. I was never a boy scout so I keep my knots simple.
Turnbuckles are eschewed. I simply pull the rope tight at the mast clamp, tie the knots and then clip the rope. Both yagis are lightweight so this method is simple, effective and cheap. It only takes a minute to level the boom.
Unlike for the 20 meter yagi, I skipped a separate lift to test and tune the yagi. I didn't anticipate any surprises. Initial tuning of the gamma match after it was secured to the mast took only a few minutes. It was to confirm that nothing was amiss in the design or construction. A few days later I did a more precise tuning that brought the SWR to nearly 1 at mid-band (21.225 MHz). At 21 MHz the SWR is 1.3 and at 21.450 MHz it's 1.6. That's very close to what was calculated for the EZNEC model using both NEC2 and NEC5.
Initial modelling of interactions indicates that the 5-element 20 meter below it does not significantly degrade pattern, gain or match. The tower guys are far enough that any interaction should be minor. However I did not check that in the model. There is interaction with the 5-element 15 meter yagi ~20' higher that skews the pattern but does not affect gain or the match.
I'll address the full suite of yagi interactions in a forthcoming article rather than deal with it here.
I do not need a separate transmission line for the yagi. I built a simple auxiliary antenna switch using an SPDT relay and mounted it directly on top of the existing Heliax LDF5 transmission line for the 15 meter stack. The NC (normally closed) port connects to the jumper going to the stack switch further up the tower; the top of the Heliax is about 107' above ground and the stack switch is at 130'. An LMR400 jumper runs down the tower to the 3-element yagi that's at about 87'. There's extra so I wound it into a several turn scramble wound CMC (common mode choke). I'll improve it later. Maybe.
Notice that the enclosure (2-piece aluminum) is oriented to place the gaps between the halves at the bottom. That makes a natural path for moisture to escape without the need for weep holes.
The wire to power the relay is less than 10' long to where is is spliced into a Cat5 control cable at the lower bracket for the 5-element 15 meter yagi (lower yagi of the stack and partially rotatable). A few more splices from there back to the shack and a change to the antenna selection software put the antenna in the list of available antennas for 15 meters.
Back in the shack I gave the antenna a spin on 15 meters and compared it to south-pointing TH6 on the other tower and at a similar height and the rotatable Skyhawk a little lower at about 71'. I found several W4, Caribbean and South American stations to compare the yagis. One comparison session isn't enough to do a full evaluation since the elevation angle of propagation varies with time of day and the season, and can differ from one day to the next.
Overall the 3-element yagi was the best of the group. The TH6 came reasonably close but seemed up to a few decibels worse. The Skyhawk was sometimes equal and other times worse, probably due to its lower height. The TH6 and Skyhawk both have 4 active elements on 6 meters, but a couple of the TH6 elements utilize traps on 15 meters that lower the efficiency and the multi-band design of the Skyhawk necessarily limits the achievable gain by 1 or 2 db.
It's interesting that the comparison can't be a rapid A-B-C sequence. Due to their different locations the cyclical QSB was not in phase. I had to monitor the waning and waxing of signal strength through a full cycle before switching to the next antenna. You would have to take the same care when transmitting and comparing the reports from RBN and WSPR networks.
On balance I'm pretty happy with the new yagi so far. It takes 1000 watts without complaint. The real test will be in a contest, perhaps CQ WW CW where it will be used in preference to the TH6 to snag multipliers in the Caribbean and South America. South is not a direction where I want to park the large yagis since that direction is not a source of many contacts, just the occasional mult.
I'll close with views from the new antenna after the final tuning of the gamma match. Why not, it was a gorgeous fall day with the trees in full colour. On the top is north (rear) view. In the near distance you can see the Skyhawk tri-band yagi a few meters lower. On the bottom is the south (front) view. There's a pretty clear shot in that direction and the two higher guy sets are off to the side of the frame. You can guess where they are from the position of the north guys in the first picture.
With this job out of the way it was on to the next item on my long to-do list, not least of which is raising the 3-element 20 meter yagi. It's a shame that the new antennas weren't ready for the CQ WW SSB contest. There are only so many hours in each day and the TH6 was already available for the southern multipliers. I am getting closer to being in a position to retire the south-pointing TH6 and be free of its interaction woes and narrow bandwidth.
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