Hi All,
Herb's method is a bit tricky. Some alternatives:
1. Use a remote relay box like a remote antenna relay, but just pick the
capacitor you want in series with the antenna. Let the others float, all
connected at the opposite end to the feed end of the antenna.
2. Use a vacuum variable capacitor driven with a DC motor. Some of these
are still available from flea markets, used parts dealers, etc. One then
has an infinite adjustment of capacity within the range of the vacuum
variable capacitor in the circuit, and changing the polarity reverses the
adjustment direction. Most of the 24 VDC motors will run slower on less
voltage, so maybe a 14 VDC power supply one uses for a 2 meter radio will
provide enough voltage. Only two wires and a reversing switch.
3. Use an appropriate air variable capacitor with a stepper motor similar
to the tuning and loading on an Alpha 87A amplifier. Again, just a few
wires for power and control of a stepper motor.
I hope these thoughts help.
73, George K8GG
----- Original Message -----
From: "Herbert Schoenbohm" <herbs@vitelcom.net>
To: "Ben Champion" <ben@benchampion.com>
Cc: <topband@contesting.com>
Sent: Wednesday, July 28, 2004 3:01 PM
Subject: Re: Topband: Remotely Switching Between Capacitors
> Ben,
>
> You can always try using half wave sections of ladderline and open frame
> relays capable of the voltages. The half wavelength line repeats the
> impedeance it sees on the other end, i.e. open or closed. Knife switches
or
> relays can be used. Depending on the type of antenna it is the relays and
> the supply voltages will be further away from the antenna thus avoiding
> severe interaction. remember to calculate the half wavelength line section
> by considering the velocity factor of the type of ladder line or open
wire
> line used. I know it issort of old fashioned but it will provide the
> ability to insert or remove the capacitor electrically. Also it allows
that
> the capacitor need not be up in the antenna but rather at the end of the
> half wave stub
>
> I hope this information may help you.
>
> 73
>
> Herb Schoenbohm
>
> .----- Original Message -----
> From: "Ben Champion" <ben.champion@verizon.net>
> To: <topband@contesting.com>
> Sent: Wednesday, July 28, 2004 1:16 AM
> Subject: Topband: Remotely Switching Between Capacitors
>
>
> Hi all,
>
> I am planning on building an antenna that requires 5 different capacitors
in
> series with the antenna to tune the whole of 160 meters.
>
> Does anyone have some ideas on how to switch between the capacitors
> remotely?
>
> Thanks in advance,
>
> 73
> Ben, AE6NY
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