Topband: Detuning/Grounding Xmit Antenna while on RX

[Jon Zaimes AA1K]

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
>
>   
>
> _________________
> Topband Reflector
>