Topband: Detuning/Grounding Xmit Antenna while on RX

[Tom W8JI]

> 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.

It is not the short that does it, but the impedance reflected to the feed 
system at the tower feedpoint.

If a short is helping it some distance from the tower, an open would help it 
1/4 wave away.

So, depending on what your radio main antenna port looks like when switched 
to receive antennas, you might be able to add 1/4 wave of coax and have 
exactly the same effect with no additional switching at all.

Otherwise, you run a risk of creating relay sequencing issues. You have to 
be careful, and you must use a relay system and a control system that does 
not hot switch a relay.