In my previous post describing my local experiences with Field Day 2016, I described my meeting several knowledgeable club members, and a very smart fellow visiting from Israel. I also described problems experienced with an antenna (‘…installed during my absence- a concave-ish flattop, center-fed dipole with about 65′ of copper wire on each side, all strung about 25′ high between tree branches. The winds were still howling; it wasn’t working properly, and as I was leaving two guys were headed out with an antenna analyzer to make some adjustments. When I returned at midnight the antenna was operational.’ Alas, I had no real idea of their investigations or the corrective actions required to make that antenna operational. Well that all changed this morning, when I received an email from Howard, my new friend from Israel. And then it all made sense.
Howard was reading my blog and saw my reference to the ‘… center-fed dipole …that wasn’t working properly.’ He was kind enough to get back to me with a full explanation of both the problem, plus a description of the solution to the problem!
Howard writes, ‘In your blog, you mentioned the center fed antenna with 65 feet on each side. This dipole was cut for the 80 meter band (3.5 Mhz). It had a current balun 1:1 between the antenna elements and the coaxial transmission line. Yes, it didn’t operate properly after testing it with an antenna analyzer. We, Jay/Rusty and I, tried to logically troubleshoot it, so we substituted each section of coaxial cable, then removed the current balun and “manufactured” a dipole connection with a plastic insulator and it was still not functioning (the same readings were obtained). The next step we took was quite interesting. Remember that each 65 foot section had a ~16.5 red wire cut for 20 M as the inner piece and the remaining outer wire was made from speaker wire (~48.5 feet). Maybe one of the wires was defective… nothing else remained in the dipole construction explaining why it was not operational… it is such a simple antenna. So we isolated the red wire from the speaker wire on one side (we choose the ground side), effectively making it an off center dipole. Reading changed, so now we were in the right direction. Next step was to isolate the inner red wire on the other side. Now we had a working 20 meter dipole and it was resonate in the SSB section of the 20 meter band, 14.200 MHz. I coiled a few meters of coax just below the antenna to the diameter of a coffee can to act as current balun (to resist current traveling on the outside of the transmission line (I call it the third leg) from reaching the radio shack. It’s this experience in the field coupled with readings from handbooks that allow you to solve problems on SOTA (Summit on the Air) expeditions. I’ve set up dozens of antennas in the field… each time learning something new. But like the boy scouts, be prepared with knowledge and experience.
Your blog is really interesting, I’ve read parts of it… and plan to read it ALL (and follow it’s updates)… Thanks to the Internet I can read your blog in the in-between moments. There is no doubt in my mind, that if I were living in Minneapolis we would be friends… your interests in the outdoors and now radio are in sync with mine.
There so much more to write about… even how the above mentioned dipole was strung up into those trees (and the sway factor), QRP, battery capacity and drain, solar power, modes of operation … but to delay this first email would be a mistake.
I enjoyed meeting you at the field day. I hope to meet you someday on the air whether it be CW HF, SSB HF or even the new mode of DMR that I’m trying out now for the first time. …we shall meet again! And if you need a partner in your backpacking adventures, give me a call… who knows I might just visit the USA more often.
Sincerely (from a long distance friend)… Howard
My sincere thanks to Howard for the detailed description of he and Rusty’s efforts to get the center-fed dipole operational. This is a good example of the comraderie exhibited between amateur radio ‘Hams’, even on a global level. Volunteers working together!