We hams often resort to the common claim to choke the “life” out of RFI on feed-lines or other wire carrying electrical current in our shack environment (and nearby) by using ferrite materials in various forms. So it’s just a reflex action to buy those ferrites to install or to make chokes. Wind-em tight. A lot. Pour on the ferrite beads. If one is good, five should be better, especially if they’re cheap. And we like cheap. Right?
Hardly! That jig can be terribly misleading, expensive or, heaven-forbid, make noise worse! That’s a jig that needs to be up.
We do it without knowing because of the genuflection to the folklore of the hobby. Without putting a meter to it to more fully understand just what the ferrite(s) we install are doing. And what we want them to do. But that is the dominant behavioral pattern of many ham operators. Add K4FMH to the list of guilty parties.
It is much easier with that handy-dandy NanoVNA that you got for not much money. IF you know how. Yes, you could read Dunsmore, Witte or Bonaguide & Jarvis. And you should. Or, have someone give you a more practical tutorial. That may well lead you to study the Masters of the VNA as shown below. As Lord Kelvin once said something like: it ain’t science if you ain’t measuring it. Sort of.
Definition of the jig is up: —used to say that a dishonest plan or activity has been discovered and will not be allowed to continue.Merriam-Webster
It was an honor to get to do a sneak-peek at one of this weekend’s QSO Today Virtual Ham Expo talks on this very subject. Mark Smith N6MTS is giving a talk entitled, Measuring Common Mode Chokes Using a NanoVNA, at 8:00 AM – 9:00 AM: 1500 UTC, 15.08.2021. This talk is worth the price of admission alone if you work HF!
I found it highly engaging, practical, informative, and he’s got the plans to build a test jig (get my title now?) to measure your own chokes before just “hoping” they will do the trick. Mark plans to post those on the Ham Radio Workbench podcast website soon. There are a lot of what look to be great talks scheduled for this weekend. But I know this is one of them because I got the chance to see it already and to share comments with N6MTS.
After you watch Mark’s talk, take a look at one or more of the online NanoVNA groups I am a member of which are listed below. Very helpful and (most always) nice members. Then take a look at Bob Witte’s book if you’re not familiar with it. It’s the preferred gateway drug to the ones by Bonaguide & Jarvis then Dunsmore. Measurement is addictive. And there’s no Twelve Instrument path for withdrawal.
The VNA Applications Handbook by Gregory Bonaguide and Neil Jarvis.
Spectrum and Network Measurements, 2nd Edition by Robert Witte.
Online groups on NanoVNAs: