[RFI] A quick Question about CMC placement

[Kim Elmore]

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/