Just home from the roadtrip to mid-Missouri…working with and for old buddy AI0O.
The scope of the project was two-fold: design and build a tower suitable for use as a dedicated 160M vertical. Then diagnose and repair the XM-240 Cushcraft shorty forty we installed a couple years back, and which had ceased to work properly about eight months later!
Most readers will wonder why these projects require any commentary, since they sound pretty pedestrian or simple. But the 160M vertical situation is compounded by the county’s zoning height limitation of only 100 feet, and our desire not to use base loading. And attempts to design a truly functional “tophat” never seemed very practical, considering the 90MPH windzone, making the hat very, very large and requiring serious tubing supplies. My approach was to simply make the top three guys part of the loading. So, with Phillystran lower and middle guys, the top 3/16-inch EHS were bolted together, then extended up and to the top of the Rohn 25G cap, and then separated by a Phillystran jumper, and then back to steel to the ground, for protection from fire and vandalism. When we were finished, I was truly stumped to find the structure resonant at 9.62 mHz! Then W3LPL reminded me of the propensity for the little MFJ box to be confused by stray broadcast RF, and with a tower only two miles away, I took Frank’s advice and used a transmitter to find the resonant frequency: 1814 mHz! What a treat to find the paper design working out so well.
Then it was over to the 90 foot tower and what we’d hoped would simply be a balun changeout, based on various reflector traffic and so forth. Indeed, we had that done in an hour and a half, without any operational changes whatsoever, and so, the decision to bring the whole Yagi down for a closer look was inevitable. I corkscrewed the beam down the top and middle guys all right, but could not get it by the lower set. In final sweaty frustration, we rigged a hunk of EHS and trammed it down, lopsided and sliding against the guy.
Once on the ground, nothing seemed evident, until we simply tested for continuity from element tip to element tip–in response to some reviews which had mentioned that the enamel wire used on the loading coils had never been cleaned before assembly. Imagine the surprise and anger when we found that none of the connections had the enamel removed before the small sheet-metal screws were inserted. So, while Rob went to the hardware store for some machine screws, to replace the sheet metal screws, I cleaned up all the connections.
Then, it was a relatively simple matter to rig a proper tram line, install enough feedline to balance the beam, and haul it back up into place. We also moved the resonant point down just a bit. All in all, fairly successful. Saturday morning found use preparing the connectors on his new SuperFlex feedlines and installing them.
Hired and brought along Benny, WB4SQC, from TN, for the trip. Having a 2nd climber and willing helper made the project much easier. I’ll be using Benny on some other up-coming jobs in TN, too!
Having lived in Missouri myself in 1981-83, and being pals with Rob, it was truly enjoyable to be out there again, despite the 100-degree days and soaring humidity. Benny was amazed to hear and watch the two of us finish each others’ sentences and casually joke back and forth using routines we’d perfected nearly 30 years ago! Rob’s older son Justin came by to help. How’d he get to be 32 years old? The passing of time and the memories when we stopped and considered them was simply amazing. As Howell remarked so long ago, time and distance does make friendships grow fonder.
Next up? Some local jobs. Then another dash West, back to TN, then to VA/MD, et cetera. The tower book should be out within six to eight weeks, according to the ARRL.
stay tuned
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