Topband: Probably-dumb question re current mode chokes on RX antennas

[GEORGE WALLNER]

On Mon, 18 May 2009 20:00:17 -0700
  "Jim Brown" <jim at audiosystemsgroup.com> wrote:
> On Mon, 18 May 2009 16:12:22 -0400, Pete Smith wrote:
> 
>>But what about the case of a different termination at the 
>>antenna 
>>end, such as a preamp or an active antenna amplifier 
>>unit?  Does the 
>>same still apply, or does the termination in the output 
>>of that 
>>amplifier attenuate the common mode currents sufficiently 
>>to make the 
>>common mode choke unnecessary?
> 
> Good question, Pete. Not dumb at all. The best answer I 
>can think of is 
> to note that 1) the common mode current is flowing on 
>the coax shield, 

Pete,

Current flowing on the outside of the coax shield causes 
radiation. The energy radiated by the coax could be picked 
up by the RX antenna. The goal is to reduce the current. 
The chokes reduce the current and thus reduce the 
radiation.

George
AA7JV