Topband: 1/2 wave tower

k6se at juno.com k6se at juno.com
Wed Aug 20 09:32:04 EDT 2003


Hi, Ron,

You wrote:

"Is it practical to shunt feed a 1/2^ vertical?"
==========
Yes, you can, but whether it is practical is a moot question.

The 50-ohm tap point for the shunt wire onto the tower will be quite high
above ground and the tuned value of the "gamma" capacitor will be quite
small.  The RF voltage across the capacitor will be very high, so a
vacuum variable is mandatory if you run QRO.  The 2:1 SWR bandwidth will
be relatively small.

All of the above will be the opposite if the structure is close to 1/4
wave electrically.

Unless the soil in your area is "very good" or better, the antenna won't
get out as good as a 1/4-wave vertical because of the low-angle "suckout"
of the radiated signal.

I feel that it would be better that you establish "ground" 1-4-wave down
electrically from the top of the tower and install a sufficient number of
radials there and shunt feed it from that point.

73, de Earl, K6SE


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