I’ve seen no mention of modeling and/or measurements performed on any of these antennas to see if they are within the match range of the KPA1500.
Jim ab3cv On Sep 4, 2020, at 2:29 AM, Victor Rosenthal 4X6GP <k2vco....@gmail.com> wrote: I had an interesting experience trying to use a balun in a very demanding situation. I'll describe it, and at the end I have a question. Antenna was a dipole with total length of 10m fed with approximately 480 ohm open-wire line. Line length was 10m. I was trying to use this antenna on 40m with a power of 1200w. The first attempt was to use a 5kw DX Engineering 1:4 balun in the shack between the open line and coax, feeding the coax with an unbalanced T-network tuner. There was a lot of RFI with computers, etc. in the shack. The antenna seemed to pick up a lot of local noise. During a period of contest operating, the balun overheated, causing soaring SWR and ultimately internal arcing. Next I added two capacitors in series with the line to tune out the reactance (the 1/4 wavelength line inverted the capacitive reactance at the feedpoint of the antenna making it inductive at the shack end). This eliminated the overheating (it ran a little warm), but the RFI problem remained. Then I rewired the balun to a 1:1 configuration. This seemed to help a little with the RFI. It made tuning easier. But the antenna was still noisy. At this point I had some really good luck and was able to purchase an old Johnson KW Matchbox, which is a link-coupled balanced tuner. I replaced the T-network tuner, the balun, and the series capacitors with this unit. The antenna is now MUCH quieter and RFI problems have been eliminated. The lesson I learned is that baluns don't work very well with high SWR, especially when the impedance is very reactive. And now for my question: did I permanently damage my balun when it overheated? If so, what is the mechanism of damage? I took it apart and didn't see any obvious signs. 73, Victor, 4X6GP Rehovot, Israel Formerly K2VCO CWops no. 5 http://www.qsl.net/k2vco/ . > On 03/09/2020 19:05, Jim Brown wrote: > <snip> A choke inserted into a poorly > matched or un-matched line is much more likely to overheat and fail. > Dissipation (heating) is addressed in the 2018 Cookbook. > 73, Jim K9YC ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to j...@jtmiller.com ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to arch...@mail-archive.com
