[BC] RF interference problem

[Jeff Johnson]

>
>Here's what I think is happening:   The FM station has a multibay antenna
>mounted near the top of the big TV tower.  Shelby's studio is about a mile
>away, so it is probably between one of the nulls and minor lobes of the FM
>antenna's elevation pattern.  The downward angle of that null/lobe will
>shift slightly with FM modulation (if the antenna is fed from the bottom
>with bays tapped off the hardline, as most are) which makes the level of
>signal at the studio vary in strength with modulation -- so there's the AM.
>
>Mark

Ah, hah! Very interesting theory! One of X-Star's station's studio (an FM) 
is at the foot of the tower. RF field strength was down where it should 
have been, but Jay had a terrible time with RF into the air console. He 
filled it with ferrite which helped greatly. However, I assumed it was the 
slight bit of AM modulation being detected. The antenna was a six bay end fed.

Why is end fed a problem in this way and center fed not?

Jeff.Johnson at goodnews.net