[RFI] 80M noise

Jim Brown jim at audiosystemsgroup.com
Tue Sep 10 23:18:27 EDT 2013

On 9/10/2013 7:20 PM, Larry Bryan wrote:
> but I did discover when I took the
> Tecsun outside that I have a large noise from the dipole coax. If I get
> anywhere near the lead in, the radio goes full scale. Same type noise I'm
> hearing on the Flex.

That may or may not mean anything. Inside the portable radio is a loop 
antenna, and it will usually couple to any wire passing by it, which 
couples any signals (and noise) current on the wire into the radio.

One thing to check -- look carefully at the Flex radio and make sure 
that the body of the coax connector for the antenna is screwed down to 

> My antenna is a Tennadyne TD-90HP800 folded dipole in a inverted V
> configuration.

Ah, the famous dummy load antenna -- that "termination" burns half of 
the TX power on some bands, which is how the antenna gets to be 

> Coax goes into a balun at the feed point of the antenna. The
> balun is part of the antenna package.

There are at least a dozen different things that are CALLED a "balun," 
and they all do very different things. The "balun" that came with the 
antenna is probably useless. Many commercial "baluns" are.

> Just looking for some feedback on this issue.

What you NEED up there is not a magic box called a "balun,"  but a 
serious common mode choke.  Study http://k9yc.com/RFI-Ham.pdf   and use 
the Cookbook to tell you how to build what you need.  I suggest one of 
the bifilar types.

I also suggest you build a much better antenna -- that dummy load is a 

73, Jim K9YC

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