Topband: Anyone purchased the ARRL book on Short Antennas for160???
Guy Olinger K2AV
olinger at bellsouth.net
Tue Jan 21 23:39:35 EST 2014
On Tue, Jan 21, 2014 at 10:12 PM, Mike Waters <mikewate at 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
All this would be why such a 160m configuration is really not a big hit and
not common as nails.
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