Bingo! One simple post, Bob, and you've covered pretty much everything anyone needs to know about wire dipole-type antennas. This is exactly the process I worked thru in deciding to build mine last year, with one embellishment - and that was to fine tune the size (I had 400 feet to work with) based on the particular frequency on which I wanted it to actually be a 1.25 wavelength EDZ, for maximum performance on 3.5 MHz (360 feet).
Like you, I am feeding it from the KPA/KAT500 but needed to use a short run of coax into the attic in order to connect to the balun, which is right above the shack ceiling. At the balanced line feedpoint (I am using approximately 160 feet of 600 ohm open wire “TrueLadderLine”) I measured the impedance with an analyzer across all bands 160 – 6m and calculated that I needed a 4:1 impedance transformer in order to present a workable match to the KAT. But I also wanted a 1:1 Current Mode balun to reduce common mode issues. Coincidentally at just that time, Balun Designs was developing a hybrid balun that actually incorporated both into one package. I couldn’t be happier with how this all came together. It is broad banded, visually acceptable and most important a great performer. 73 Lyn, W0LEN "Bob McGraw K4TAX" posted: As discussed below, what ever you wish to call it, the antenna that is, being: a G5RV, a double Zepp, an all band antenna, a center fed dipole and a few more brand names, the center fed dipole with with a balanced feed and a suitable balun can be matched on all bands, 160M - 6M with the tuner in the K3S or the KAT500. There are no magic numbers regarding lengths. There are two questions to answer: (Q) How long should the antenna be? (A) As long as one has for available space. (Q) How long should the feed line be? (A) Long enough to reach from the feed point to the station operating position. Now, the length of the wire is relative, being the most one can put up in the clear. The feedline, be it true open wire of about any impedance or ~450 window line or 300 ohm transmitting twin lead is all that is necessary. Agreed, some combinations of lengths are more difficult to match. If this occurs, then add some 4 to 6 ft of feed line length, or add 4 to 10 ft to antenna length. Or shorten the feed line length. The point being, if one can attain a 2:1 match or better it will radiate quite efficiently. If your amp won't tolerate this, then a bit more attention to length is required. The topic of what balun to use is an extensive discussion. Most baluns are OK, while some are just purely awful. Some may not alone provide the necessary common mode current rejection. Power rating of baluns are for a MATCHED condition, to which we most always use them in a highly unmatched condition. Thus the suggestion is one consider a much higher power rated balun than one intends to run. My reference to balun usage and design is https://www.dj0ip.de/balun-stuff/. The issue of using a balanced feed system is much easier than the "old ham lore" will stipulate. Just use common sense. It ain't rocket science folks, nor does it require a Ph.D to make it work and work quite well, I might add. Yes, it is very much OK to bring the balanced feed line all the way to the operating position where it then attaches to the balun of ones choice. It is not necessary to have the balun outside and bring the feed point in via a length of coax. If one is going to use open wire line or balanced line, then don't screw up the system by introducing a length of coax to go from the station to the balun in the outside world. There will be an unbelievable amount of high SWR on that coax {and equal amount of loss} and likely a high amount of common mode current. Do it correct the first time, enjoy the very favorable results, and forget about the "old ham lore" for it is not correct! I've only been doing it this way for some 50+ years. I sit here today with a very modest station. Then antenna is a 256 ft center fed wire with 450 ohm window line. The center of the antenna is 50 or so feet and the feed line is what ever it took from a 100 ft roll to get from the feed point, through the attic eve, drop down through the ceiling to the operating position. There was about 25 ft of 450 ohm window line left over. I easily work all modes and frequencies 160M - 6M up to 500 watts from my KPA500 and KAT500. The antenna and feed line have been in the air and in place for 10+ years and I expect it to last longer than I do. Yes, when it rains or snows the SWR goes up, but so what? That is what the dang tuner is for and it does an excellent job with just the touch of a button. If you only have 90 ft for the antenna, that's OK, If you only have 55 ft for the antenna, that's OK. The feed line goes from point A to point B, whatever that length might be. Shorter lengths of antenna become a real challenge to get a good match on frequencies lower than the resonant length but it will work if you can match it. For get about the charts, the computer modeling, and put up what you can, in a reasonable fashion, and begin to enjoy ham radio. 73 Bob, K4TAX ______________________________________________________________ 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
