Topband: Measuring Common Mode Chokes (Michael Tope)

Dick Bingham dick.bingham at
Fri Dec 27 23:43:40 EST 2019

Hello All

Maybe the proof of the pudding is to apply the CM-Choke
at the end of your TX/RX coax and replace the antenna
connection with a 50 (75) Ohm load.

Then compare any received signals at the receiver with
and without the CM choke against what you see with the
load applied directly at the receiver.

If things are 'cleaner' with the CM-Choke installed that's
great. Then you can compare other CM chokes (different
core mixes / turns / etc) across the freq-range of interest
to obtain the performance you desire.

A wide-band RX makes this evaluation markedly easier
than making many spot-freq measurements.

So far, using several CM chokes on the feedline and connections
to the receiver, I have been able to significantly reduce garbage
from S-9-plus to about S-5 for a single remaining bad actor
repeating itself across 80-meters - something now getting 'in' via
the antenna and not thru CM currents on the transmission line.

Once the remaining bad-actor is found/killed, 80-meters should be
delightfully usable .

73 to every one


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