[TowerTalk] Tower location and house noise

[Wes Stewart]

Yeah, well, this thread has gotten slightly corrupted.  As I followed it, the 
object was to place a tower well away from the house (source of "noise") and 
then the discussion of transmission lines ensued.  There seems to be an idea 
that a long transmission line is going to "pick up" noise unless it is choked, 
as if it's a beverage or something. I fail to swallow this idea, hence, my 
comment about worrying about signal+noise propagating normally inside the line.

A comment was made:

    "Not so sure what you mean by "noise inside the line." It has to get
    "inside" somehow, from whence it is choked almost any convenient place along
    the line prior to the rig connection."

Which of course makes no sense and to which I foolishly failed to respond to 
with enough specificity to avoid another unneeded lesson from you.

I regret the oversight.

Wes  N7WS

On 5/25/2017 10:42 AM, Jim Brown wrote:
> On Thu,5/25/2017 9:57 AM, Wes Stewart wrote:
>> Not sure what you mean either. "Inside" means... well.... inside, i.e. a 
>> differential-mode path consisting of a center conductor and the inner surface 
>> of the outer conductor.
>
> Common mode current, whether on the outside of the coax shield or on the two 
> conductors of parallel wire line, is the result of un-equal currents on the 
> two halves of the antenna, and the common mode current makes the feedline part 
> of the antenna. With no choke at the feedpoint, received noise current on the 
> feedline couples to the "intentional" antenna, so it adds to what the 
> intentional antenna couples to the feedline in differential mode. By 
> reciprocity, the mechanism is present both on TX and TX.
>
> Common mode current on the feedline is the result of any imbalance in the 
> antenna system. A common mode choke at the feedpoint effectively decouples the 
> feedline from the antenna by presenting a high impedance to common mode 
> current, reducing the common mode current to near zero, thus forcing the 
> current in the two halves of the antenna to be more nearly equal. Without the 
> choke, currents in the two halves are not equal at the feedpoint, with the 
> difference flowing as common mode current on the feedline.
>
> This mechanism has been understood for a LONG time.
>
> 73, Jim K9YC
>
>
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