[TowerTalk] Choking on chokes

[Ian White]

>
>Just had a thought. Do I need to choke my rotator control cable too? 73,
>David, AA9G
>

You certainly shouldn't need to do that. 

Let's think about this, because RF current on a rotator control cable can't just appear out of nowhere. The defining feature of current is that it must have come *from* somewhere and be flowing *to* somewhere else... so where would this unwanted current be coming from? 

The only possible source of RF current is at the Yagi feedpoint, where a design error or a bad choice of balun might cause unwanted common-mode current to flow along the feedline, the boom and the mast... so the feedpoint is also where the solution must be found. Choking the rotator cable would only be treating a symptom, while ignoring the much bigger root cause.

[Afterthought: another potential cause of common-mode current on the rotator cable could be a complete break in the shield of the coax feedline, forcing RF currents to find a return path outside of the coax. But once again the rotator cable would only be a symptom, not the root cause.] 

I guess the real point is that we can work out quite a lot by standing still and taking a moment to think.


73 from Ian GM3SEK