Topband: Noise Problem Solved

[Joe Giacobello, K2XX]

  Several weeks ago, I posted the following on the reflector regarding a 
noise problem I've had all season long:

> Regarding noise on 160M, I have been consistently observing all season 
> long a broad signal, reminiscent of a plasma TV, centered around 1836 
> KHz.  Since it seems to be on 24/7 and my closest neighbor is a half 
> mile away, I don't think it's a TV.
>> It's more or less centered on 1836 and is quite wobbly and varies in 
>> amplitude and frequency.  It's about 2.5 KHz wide, and it doesn't 
>> vary in strength when I change directions on the RX array. 

Well, whatever it's source is, it was getting into the shack via a 
common mode path.  I use about 300 feet of flooded RG-6 between the RX 
4-square and the shack.  There was no common mode choke in the system.  
It just occurred to me this morning that common mode transmission might 
be the problem.  The signal was reduced by at least 30 dB and virtually 
eliminated by winding about eight turns of the coax (RG-59 inside the 
shack) around a #31 mix, 2.5" ferrite core.  Originally, I tried up to 
six of the common snap-on, split core ferrites (presumably mix #43) with 
very little effect.  The difference with the #31 mix was like day and night.

I thought my experience might be of use to others who have reported 
similar problems.

73, Joe
K2XX