Topband: Help Needed Decoupling the TX Antenna

[Herb Schoenbohm]

Eric Rosenberg wrote:
> My noisy urban lot is small (40x140), and the Pennants are awfully close 
> to the TX antenna. (inv-l's on 160 and 80, 1/2 square on 40).
>
> I need to decouple the TX antenna when listening on the Pennants, but am 
> not quite sure how to do it.
>
> Eric,
>   
> Thanks for the frequent DC multipliers in various contests. Before embarking on elaborate switching you might do a few test to see how much random noise is contributed by the Inv L's  to your RX antennas.  Having an old fashion porcelin knife switch (like we had on the farm in North Dakota to turn on the milking machines) may be available or you could build one with fiberglass strips and copper flashing pieces....and have an assistant do the switching while you are listening. Opening up the fed point match or grounding either end or both is worth a try. I think the far end of your Inv-L is close enough to the ground to reach with a "earthing" connection.  Also a lot may depend on common mode rejection to the pennants feedline.  Insertion of toriods or a ground isolated 1:1 balun may even help taking down the noise pickup on the coax itself. If you find that there is indeed noise from the TX which common mode isolation can not cure then a 12VDC high current relay will be required.  Some  have reported success with inexpensive automotive DC relays.  They can handle the current but for TX voltage I haven't any idea...as it all depends on your feed/match system.
>   
Good luck,

Herb, KV4FZ