[Elecraft] OT: How do you measure common mode current?

[Geoffrey Mackenzie-Kennedy]

Steve, VK2SJA wrote:

> I've done some web surfing re this issue and it appears that for EMI
> testing they use a wide band RF pickup of some sort and a sprectrum
> analyzer. Given that I don't have a spectrum analyzer and that I'm not
> concerned with laboratory accuracy is there a simple way of finding out
> the level of common mode current floating on your coax?

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Yes, there is a simple device that is very easy to build which will detect 
common mode current on the outside of coax, and can be thought of as a 
'current transformer' plus detector driving a meter. Without  calibration, 
which would require other test equipment, the device will let you know if 
there is common mode current flowing and whether it decreases or increases 
after making a change. Other versions are useful for detecting RF current in 
things such as above ground telephone cables which could be affecting an 
antenna's performance.

Please let me know off- list if you are interested in seeing details.

73,
Geoff
GM4ESD