[TowerTalk] To get a truly balanced antenna feed

[Ian White]

VE7RF wrote:

>##  Ian mentions the current.  If that’s the case, why not just 
>measure the current with a clamp on ammeter.... at say 
>several random places on the coax feedline ?   

That is exactly what I try to do - see my website: "Clamp-on RF Current Meter - *the* most useful tool for RF interference troubleshooting."
http://www.ifwtech.co.uk/g3sek/clamp-on/clamp-on.htm

A perfectly functional instrument can be thrown together in half-an-hour. The passive diode detector will typically read from about 25mA up to 1A. It is also possible to build a much more sensitive log-scale instrument based on an AD8307 detector chip (or similar) which will read down to 1mA, but with reduced resolution.

> Then we have yet another issue to deal with, and thats 
>what if the coax braid is  bonded to the top of the tower ?   
>If a lousy CM choke balun  is used at the ant feedpoint, 
>and  braid also bonded to top of tower, we can then have
>a case where  CM current is now flowing down the tower.

Well jes' don't do that! Don't use a lousy CM choke at the feedpoint, use a good one; and if in any doubt, use another CM choke (which doesn't have to be so good) just above the point where the braid is bonded to the tower.

Or best of all, measure the CM current both before and after. 


73 from Ian GM3SEK