Topband: decoupling Inv L for loop on Rx

[John Randall]

Reading through the latest batch of emails, I realised that I may have to decouple my INV L antenna on Rx sothat I can rx on my loop. The loop will be on a 10ft pole appox 20ft from the INV L, so the question is would a simple grounding of the tx antenna either at the pole or at the shack work, and what else can I try ?
I saw this post from Marcus as below.
73John - M0ELS

I have a small rotating terminated loop receiving antenna which is located only 
20 feet from a Inverted L - FCP (folded counter poise) transmit antenna.  

The amount of noise re-radiated from the inverted L to the terminating loop is 
very high, over S9. ( receiver sensitivity -128dB at BW of 500 Hz.) 

Experimenting with different ideas I found what worked for me was to short the 
transmitting antenna to ground right at the point the coax feed line enters the 
house.  The entry box where the coax connects to go through the house wall is 
connected by a one foot #6 wire to a 8 foot ground rod.  I installed a vacuum 
relay at that point which on receive, closes the relay and shorts the transmit 
antenna to ground.  I used the T (transmit signal line in my transmitter) to 
drive a transistor switch to close the vacuum relay on receive as the T line 
opens the relay 5 mS before the transmitter actually begins to transmit RF and 
the T line also keeps the vacuum relay open until the RF diminishes to zero.  

The result, zero re-radiated noise from my transmit antenna, the terminated 
loop acts like a terminated loop with a deep null in the back lobe.  

This may not work with your particular set up but easy to try.  You may have to 
short your transmitting antenna right at the antenna not at the entry to your 
radio shack?

Good luck.

Markus  VE7CA
Web  ve7ca.net


Digitally signed mail - John  M0ELS

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