Hi Bob,
You could use a vacuum relay and key it from the keyer or rig line that
is timed keying (such as for an amp). You want it open when transmitting
of course.
Might even be able to use a smaller non-vacuum relay such as the PC ones
used in Top Ten and other relay boxes.
Also can put this relay at the shack end of your feedline, depending on
the feedline length. If it is a quarter wave line (or odd multiple),
OPENING it in the shack will SHORT it at the tower end.
I discovered that quite by accident -- before I learned the theory from
WW2Y -- at my Bear, Delaware, QTH in the 1980s. I had a short Beverage
that ran very close to the shunt-fed tower (about 50 feet) and when I
switched the feedline out on the antenna switch in the shack the noise
went way down. It was about 200 feet of CATV hardline, so a bit longer
than 1/4 wave electrically but nevertheless it just happened to work at
that length.
If the feedline was 1/2 wave or a multiple, then you could short it out
in the shack and it would short it out at the tower end.
You can also use a capacitor or coil (or both) at the tower or at the
shack end of feedline to detune. ON4UN describes these in his book.
73/Jon AA1K
On 11/15/2013 10:46 PM, Bob Garrett wrote:
Greetings Topbanders,
I have an 85 foot shunt fed tower that I use on TB. I have a HI-Z 4 Square
and some short beverages. The performance of the RX antennas definitely
improves (less noise and better directivity) when the TB vertical is shorted
to ground. What is the easiest mothod to short the vertical to ground? Do
I need to put a relay at the base of the verticaland activate a relay? I'm
using a Microham Digikeyer for myinterface and the rig is the FTDX-5000.
Perhaps a set of contacts on one of those units could do the trick. Any
assistance appreciated.
73, Bob K3ULeither
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Topband Reflector
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