[Amps] RF in the Audio

dalej dj2001x at comcast.net
Sun Sep 25 04:06:01 PDT 2011

On 9/23/2011 3:08 PM, Robert Kirkland wrote:
> I think your quite right in "seriously choking off your feeders". But 
> please tell me how to use toroids on a 600 ohm open wire line. 

>Wind a bifilar choke using 12-14 bifilar turns of #12 THHN on a #31 
>2.4-in o.d. toroid. It introduces a small mismatch (Zo approx 100 >ohms), 
>but only about two feet of line. Photos and details in the latest 
>version of my RFI tutorial. http://audiosystemsgroup.com/RFI-Ham.pdf

>73, Jim K9YC

I can say for my own experience that this technique does work.  I have a Palstar BT1500A double L network balanced line tuner and I added a choke balun as per your suggestion above, about 4 feet from the tuner posts, the tuner now is tuning entirely different than before and much wider range of bands and I now no longer hear the two local radio stations S-9 mix at 3790 and a S9+10db third harmonic 3990, which was my original reason for adding the choke.  The choke balun works on open wire feedline using a balanced L network tuner.  BTW, this "trick" was suggested by Paul at Palstar.  

I'll check out your tutorial Jim.  Thanks.

Dale, K9VUJ

More information about the Amps mailing list