Common Mode RFI, Chokes and the MFJ-854

The MFJ-854 RF Current Meter can detect common mode on a wire

Here is one of the best reasons why MFJ should be praised and not scorned. I have been reading about Common Mode Noise / Interference for years – most notably on the W8JI and other web sites, and while there are many suggestions on how to mitigate it using ferrite snap on chokes or toroidal cores, I just found a web site where the fellow mentions this very cool “Common Mode Sniffer”:

One of the things I can do this weekend is measure the two lines that go out to the receiving antenna and also the UrbanBeam.

W8JI does have a great write up on the subject, and after all – he is the designer of several excellent DX Engineering products

Jim Brown – a local here in the Bay Area and one I’ve had some nice chats with might have the best presentations and write ups going. He really, and I mean really has dug into this topic from a very serious engineering standpoint. Anyway – I have read most of these pages and docs before, but the missing link has been measuring before and after trying to mitigate Common Mode – IF you even have it on your cables (coax and control lines – basically anything with wire).

Jim’s fantastic “Cookbook”. Just what everyone needs in Ham Radio – that’s for sure! And here is a doc for just receiving antennas:

I will report back on what I find. What is super cool is that I can measure the feedlines before and after trying adding the ferrite chokes.


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