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
“The further a society drifts from truth the more it will hate those who speak
it.”
George Orwell
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