On Tue, Jan 21, 2014 at 10:12 PM, Mike Waters <mikew...@gmail.com> wrote:
> Wouldn't feeding it up high in the corner like that at least eliminate the > need for radials? > Yeah, but this is 160, and if you can get the bend up 75 feet or so you are feeding a half-size doublet that consists only of a pair of 1/8 waves. Really a very different antenna story on 80 meters where the same 75 feet can get your vertical and horizontal to a 1/4 wave each. On 160 with a split 1/4 wave L you get a feedpoint at the bend of Z = 12 - j1100 ohms over "average ground". To tune out all that capacitive reactance will employ ~ 94 uH coil or its various equivalents with transformers, feedline tricks, etc, making the match quite narrow, along with many opportunities to generate loss if the whole thing isn't done tightly according to the book. Without any loss factors and with a perfect tuning inductor the 2:1 bandwidth at 12 ohms at feedpoint is only about 10 kHz. Unmatched 50 ohm SWR is over 4:1. Current at feedpoint is over 11 amps for 1500 watts, meaning any balun device must be designed for the heavy current ** at 160m **. Also meaning that a lot of the "balun" stuff I've seen will burn and/or leave huge amounts of common mode on the feedline. If you use balanced line, the typical "450" window line will have an impedance of 13k a quarter wave away. All this would be why such a 160m configuration is really not a big hit and not common as nails. 73, Guy _________________ Topband Reflector Archives - http://www.contesting.com/_topband