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Topband: Switching in Extra Antenna Length

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Subject: Topband: Switching in Extra Antenna Length
From: (Ford Peterson)
Date: Tue, 2 Jul 2002 17:13:37 -0500
> I plan on running the control wire up through the center of
> the vertical and it will peek out at the very top of the
> tubing and connect to the operating coil of the vacuum
> relay.  In addition, I will be using decoupling methods to
> inhibit RF from coming down the control wire into the shack.
> This seems to be a very easy way of using this  vertical on
> 2 bands.  Does anyone see any problem with this?
> K2WH

Hmmm.  I pondered trying this stunt on a slightly different design and
rejected the project for several reasons:

1) The voltages at the top of a resonant 80 vertical, at resonance, are
going to be almost impossible to manage--especially at 1KW or more.  The
vacuum relay will most certainly be useless on 80 as a switching method.
Managing those voltages in an enclosure to protect stuff from the elements
will render the device an ozone generator.

2) Maintenance--you develop a problem during topband season (winter) and you
are down for a long time.

3) Isolating the control voltages may prove more difficult than at first
thought.  Even with a large choke at the base of the vertical, ugly voltages
can develop along the length.

4) Refer to #2
5) Refer to #2
6) Refer to #2

My $0.02


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