Topband: Common mode chokes

[GEORGE WALLNER]

>On Fri, 10 Jul 2009 12:00:57 -0500
>K4SAV <RadioIR at charter.net> wrote:
> Thomas Damboldt wrote:
>>If I connect my 
>>receiver with a very short feedline (say 1m), to the >>antenna, I should not be receiving much common mode >>noise. Is that true?
>> Certainly worth trying.
>>  

The RX antenna needs the feedline because we have placed 
it away from the shack/house -- all the noise sources. In 
a real world environment the length of the line is a 
given; we do all the things described in this thread to 
ensure that it does not carry and radiate the noise we 
moved the antenna away from in the first place.

On a separate note, I have been experimenting with twisted 
pair RX transmission lines. I have used a twsited pair 
removed from a CAT5 cable. With a well balanced 
transformer and a common mode chocke at each end, it seems 
to have very high common mode rejection (i.e. I have not 
been able to measure it). Loss at 1.8 MHz is about 0.7 dB 
/ 100'. Note that for good common mode performance, the 
line should be away from other conductors.

George
AA7JV