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 <[email protected]> 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 > > ______________________________________________________________ > Elecraft mailing list > Home: http://mailman.qth.net/mailman/listinfo/elecraft > Help: http://mailman.qth.net/mmfaq.htm > Post: mailto:[email protected] > > This list hosted by: http://www.qsl.net > Please help support this email list: http://www.qsl.net/donate.html > Message delivered to [email protected] ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[email protected] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to [email protected]
