[Elecraft] Coiled Coax Choke

[Walter Underwood]

A choke in the middle of the transmission line could help, but the usual configuration is a current balun at the antenna to reject common-mode signals at the source, plus an optional choke at the entrance to the shack to reject noise picked up by the outside of the coax shield.

A coiled-coax choke works OK, but you get the best rejection from a toroid-based choke or balun. I’ve had good results with the ones from Balun Designs (http://www.balundesigns.com).

Putting a Balun Designs balun at my dipole dropped the noise by 6dB.

I highly recommend K9YC’s super-detailed explanation of fighting noise in your antenna and elsewhere in your shack.

http://audiosystemsgroup.com/RFI-Ham.pdf

wunder
K6WRU
CM87wj
http://observer.wunderwood.org/

On Oct 20, 2014, at 7:28 PM, Dauer, Edward <edauer at law.du.edu> wrote:

> I am thinking of adding a coiled coax common-mode choke to my system.
> Presently it goes K3-KPA500-KAT500 then 100 ft coax to the base of an
> inverted Vee¹s center support pole (collapsible fiberglass), then 30 feet
> up the pole to a 1:1 balun feeding a fanned 10-15-20 Vee.  The idea, for a
> couple of reasons, is to put the choke at the base of the pole, something
> I haven¹t seen discussed in the literature.  Two questions I am wondering
> about:  1. The choke would be 100 feet from the tuner and about 25 feet
> from the antenna/balun.  Probably not as good as having it right at the
> Vee, but is that compromise worth while?  2.  For appearance sake I am
> thinking about winding the coax around the base of the support pole.  It
> is 2 inches in diameter but I could slip a 3 inch PVC over that section to
> increase the diameter.  Anyone know an algorithm for determining the
> number of turns in the winding if I do that?  I would be much obliged for
> any thoughts and suggestions . . .   Tnx!
> 
> Ted, KN1CBR
> 
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