Jim:
I helped install shunt feeds for 160 and
80 meters at WB0DRL in 1992. The tower
was 75 foot high Rohn 25, with a Cushcraft
6 el 6M yagi at the top(34 ft boom) and a 6 el
Hy-gain 6M yagi mounted at 40 feet.
36 sixty foot long radials were used.
The 1.8 MHz tap was connected at the
top of the tower, the 3.5 MHz tap was
at 30 feet. Spacing was about 36 inches
on 1.8 MHz, 15 inches on 3.5 MHz. A
gamma match used a 500 pF variable
cap(can use a 250pF) on 1.8 MHz, and
an omega match with two 150 pF variables
for 3.5 MHz. The best SWR obtained on
160M was about 2:1, later the 80M shunt
feed was dismantled and used to make
an omega match for 160M which allowed
a 1:1 match. The operating bandwidth on
160M was about 30 KHz.
The shunt fed tower was used under my
call sign in the 1992 ARRL 160 'test
and as WA0TKJ in the 1993 CQ160CW
and radiated a competitive signal, with
QSOs into Europe, Asia, Africa, and Oceania
despite lots of sun spots!
73,
Jon NO0Y
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