[bars] Fwd: Monitor RFI

[Andy Wallace]


Gary W1GFF’s issue with RFI into his computer monitor sent me surfing. This site has some interesting tips about suspecting that it could be common mode current from the transmitter. Here is info on making a detector for that.

 

rfi - How to detect common-mode currents or “RF in the shack”? - Amateur Radio Stack Exchange

 

A comment here said that connecting an SWR analyzer and running your hand along the feedline could be a good test for this (without needing a transmitter). Gary, the fact it happens on 20 is the biggest clue. How is the native SWR there? A field strength meter might help, too. Good luck – sometimes these things are hard to troubleshoot but at least these devices are in your house, not a neighbor’s!

 

Here is K9YC’s excellent presentation on making your own coax chokes.

 

Microsoft PowerPoint - CoaxChokes-SCRZ.ppt (qsl.net)

 

W1HIS’s presentation on common mode chokes is here:

Common-Mode Chokes - Yankee Clipper Contest Club www.yccc.org › Articles › W1HIS › CommonModeCh... (google.com)

 

And as people have mentioned, the #43 cores are not as good as the #31 for the lower HF bands. I have ordered 31s direct from Mouser and Digikey by putting in the Fair-Rite part numbers in the search. Do NOT be ripped off by ebay and other sellers who call these things “FT240-31” and whack you $20 for a single donut. They are about $5 at the previous sites.

 

Hope these help.

 

Andy

KA1GTT

 
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