Topband: Pre-Amp Shielding

[Doug Waller]

The line loss has little to do with the problem.  Its the signals leaking
into the coax thats the killer.

I thought coax was well shielded until I put 40 db of preamp in the shack.
The RG-58 picked up broadcast stations at 20 over, with no antenna connected
to the coax.  RF chokes on each end of the coax almost solves the problem,
but my next step is to replace the coax with a double shielded type.

RF chokes that work well at 160m must still choke well in the broadcast band
to kill the noise.  FT150A-F toroids with 15 turns of mini-coax makes a fine
choke.  I now hear very well with the phased loops with an 18 db
preamp/hi-pass filter at the feedpoint.

73, Doug / NX4D

----- Original Message ----- 
From: "Fred Cresce" <fcresce at comcast.net>
To: "Top Band Reflector" <topband at contesting.com>
Sent: Monday, September 22, 2003 8:20 AM
Subject: Topband: Pre-Amp Shielding


Hi Tom
I'm sure some of the other folks on this reflector would agree that the line
loss on your coax run for the K9AY loop is very minimal. I would stick my
neck out and say less than a dB. I know that for VHF and above we need the
preamp right up there, but not  at 160M. We're dealing with more atmospheric
noise than anything else.
Fred
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