> adjust the loop length for resonance at your desired op frq. Don't use
any
> tuners. The loop will work well on harmonically related frq.
My horiz loop is cut for 160m and the harmonic falls on 3520khz. The
feedpoint impedance of a loop on it's fundemental frequency is about 100
ohms. Harmonics will result in impedances of from 100 to 300 ohms. Feeding
the loop with 50 ohm coax will result in swrs of from 2:1 to 6:1 on higher
bands and a severe problem with feeder radiation since the loop is balanced
while the coax is not.
Currently, I feed my loop with a 4:1 W2DU current balun at the corner and
RG-213 down to the shack.This produces a balanced system and swr of less
than 2:1 on all bands. I strived to achieve the best match on 3520khz thus
producing the best matches within the cw portion of the higher bands. 160
is my worst match and although my Omni is forgiving, I still use a tuner on
160 to keep it happy. No other band requires a tuner except 30m.
I have tried using open wire feeders. This works but requires use of a
tuner on every band of course. Also I've used dual 95 ohm (RG-62) coax with
the balun in the shack. This worked qite well and allows the balanced
feeders to be buried or taped to your tower.
TenTec rigs don't use any "fold-back" system in their final amps. This
allows you to run full power in spite of a slight mismatch. Just keep an
eye on the collector current that it doesn't exceed 20 amps.
Steve Ellington
Amateur Radio Operator N4LQ
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