[TowerTalk] Auto tuners, Baluns and open wire feeders

[jimlux]

On 7/17/18 3:13 PM, Jim Brown wrote:
> On 7/17/2018 1:50 PM, jimlux wrote:
>> Yes, you need a choke on the coax at the tuner (which is what forces 
>> the above statement - you don't want currents going down the outside 
>> of the coax). 
> 
> A choke at the tuner is NOT equivalent to a choke at the feedpoint 
> (although a choke both places is not a bad thing).
> 
> The length of feedline between the antenna and the choke IS PART OF THE 
> ANTENNA, so noise picked up on that length of line is coupled to the 
> antenna, then comes back down the line (as a differential signal) to the 
> receiver.

I agree - I was assuming the "feedline" is short (single digit feet) and 
reasonably balanced (so that environmental noise would couple equally to 
both sides).  And, of course, the tuner itself is sort of an asymmetric 
thing, and if it has a conductive box (or a ground plane under the PWB 
inside a plastic box), then noise could couple in that way too.