> I have several 160 and 75 meter antennas. I'd like to be able to cover
> most og these bands with the least involvement from the shack after the
> initial set-up.
>
What I do on 40, 80 and 160 meters is to tune the antenna for a
match at the bottom of the band, and then use three relays to
switch in combinations of a binary series of capacitors.
For example, an 80 meter inverted vee is tuned to 3.500 MHz
by trimming the wires. A series string of 470 pF, 1000 pF,
and 2200 pF is inserted in series with each leg of the inverted
vee. Each capacitor is shunted by a normally closed relay.
The two 470 pF capacitors are on one DPDT relay (used as a DPST).
Similarly, the other two relays handle the 1000 and 2200 pF pairs
respectively. The relays can be individually energized to
unshort a capacitor pair and place it in the circuit.
The eight combinations cover the whole 80 meter band
(3.5 to 4) in eight subbands. There is also a 40 meter inverted
vee physically at right angles to the 80 meter vee. The two
vees are electrically connected in parallel The capacitors
also tune the entire 40 meter band easily. There originally
was a 4th relay that disconnected the 80 meter vee when using
40 meters. I observed that this relay made absolutely
no difference, indicating that the 80 meter vee doesn't interact
with the 40 meter vee.
Note that the relays must be at the feed point, not in the shack.
The capacitors are CDE MC series and the relays are Omron
MJN series, both available from DigiKey. Works at full legal limit.
Rick N6RK
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