Hello BVARC,
Following my talk on CMC (Common Mode Current) chokes here are some possibly helpful links.
FT240-31 style fair-rite (2.4 inch mix 31) toroid core from Mouser Electronics
$6.35 each in single quantities (plus shipping). It's important to order these from a reputable source as cheaper knock-offs abound.? Email me if you are interested in placing a group order and how many you want.? We could also order some high quality teflon insulated coax and UHF connectors to form a complete kit and build some together at a future meeting.
Commercial alternatives:
I've used the MyAntennas Common mode choke (RF Isolator) at my antenna feedpoint with good results. I was asked about the effect on the antenna SWR.? The antenna is an 80-10 OCFD and adding the choke shifted the resonance on 80 meters so the coverage across the bands aligned better. It greatly reduced the RFI issue with our whole house smoke alarm, and also lowered the receive noise level.? End fed or off center fed antennas are much more likely to create RFI issues due to so called "common mode currents".? Every situation is potentially different so how much this will help in your shack depends.?
For "random wires" and end fed half waves which are popular for POTA preventing the feedline from radiating as part of the antenna and using a dedicated counterpoise can provide better results.? Alternatively, if you want your coax feed line to act as a radial (or radiator) you can place the choke nearer the transmitter to prevent RFI problems.
73, Peter K1AV
Peter Sichel K1AV