[RFI] A quick Question about CMC placement

[Edward Mccann]

Absolutely it matters!

Best placement is at the feedpoint, if the antenna can stand the weight. Second best placement is at the feedpoint and Another at the shack window.

Think of that span of coax feedline from feedpoint to shack collecting CMC from every source it can find!

Been there, done that, got the tee-shirt.

73,

Ed McCann
AG6CX

Sent from my iPhone

> On Jun 28, 2021, at 9:30 AM, Kim Elmore <cw_de_n5op at sbcglobal.net> wrote:
> 
> Having just come off of filed day, the value of a CMC was, for the umpteenth time, demonstrated in the most practical sense. We were operating an FTDX5000MP for the CW station. We probably had the best antenna of any station at the site, up about 70 ft or so. But we had RFI in the shack: we could hear big thumps through the headphones as we keyed the rig and the WinKeyer would occasionally lose it's mind as would the laptop we were using for logging.
> 
> The owner of the rig had a CMC choke he'd left at home, went home and got it, we inserted it and, like magic, all RFI problems were gone!
> 
> His was straight out of the latest K9YC cookbook CMC (14T of RG-400 on a type 31 2.4" OD ferrite core) in a nice, weatherproof box and the only place it would fit was outside where two cables had to be connected together with a PL-258 (barrel connector). We had a brief discussion about the optimal placement of a CMC: where in the line should it go? I take the view that it should be at the antenna feed point, but he thought somewhere in the middle of the line is optimal. Now, though, I wonder of it really matters where it is in the system. Does it? If so, why?
> 
> Kim N5OP
> 
> -- 
> Kim Elmore, Ph
> 
> Kim Elmore, Ph.D. (Adj. Assoc. Prof., OU School of Meteorology, CCM, PP SEL/MEL/Glider, UAS, N5OP, 2nd Class Radiotelegraph, GROL)
> 
> /“I occasionally play works by contemporary composers and for two reasons. First to discourage the composer from writing any more and secondly to remind myself how much I appreciate Beethoven." – Jascha Heifetz/
> 
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