[Elecraft] RF feedback?

[Jim Brown]

On Tue, 14 Jul 2009 18:26:15 -0400, K2QI wrote:

>Antenna system is a Tarheel 100A screwdriver mounted on a tripod on my
>balcony.  The balcony is about 40 feet away from the station.  The antenna
>is fed with good quality Times Microwave LMR-400UF.  The last 20 feet of it
>were wound into a common mode choke using 4" PVC.  The antenna does not have
>a very good radial system; about 10 strands of 20g wire cut to about 12 feet
>in length.  I do have a 66' length counterpoise but have not laid it yet due
>to the size restrictions of the balcony (5' x 12').  The antenna's control
>cable was also decoupled via a ferrite choke.

You're running 1.1kW to a screwdriver with essentially no radial system and 
you're surprised that you have RF issues?  THAT'S your problem!  Build 
yourself a real antenna. This antennna is a disaster -- it's using every wire 
in your house and shack as a counterpoise. No wonder you have RF issues! 
Chances are that you're also lighting up every other piece of electronics in 
the building. 

Screwdriver antennas are designed to work against the body of a vehicle (and 
a pretty beefy vehicle at that) as a counterpoise. They are EXTREMELY 
compromised antennas. The "choke" you describe is next to useless. 

If your can find structural steel on your balcony, you should use that as the 
counterpoise for this antenna. The building will still be pretty hot with RF, 
but it should work a lot better than what you have now. 

>Please clarify the K3 pin 1 issue; 

Study the reference I posted.

73,

Jim K9YC