[RFI] Coaxial Choke

[Jim Brown]

On Wed, 15 Apr 2009 11:08:05 -0400, Andy wrote:

>> The material in the ARRL Handbook is woefully out of date and quite
>> inadequate.

>I'm not sure if "out of date" is exactly right in this context (neither the
>coax nor the theory changed, did they?), but I believe you are right that
>air would coax chokes are inadequate for HF.  

I am sure, and I'm become an authority on the subject by doing a lot of 
scientific work on the topic and publishing it. 

>OK for VHF, maybe for the
>upper HF bands too, but not as a general HF band choke.  Not nearly enough
>impedance to choke off common-mode currents.

>There was an email thread about this on one of the many other email lists I
>subscribe to, saying pretty much the same thing.  To be effective at HF, one
>must use some ferrite core(s) to make an effective choke.

Gee -- since when is science defined by what one reads on email lists? What 
happened to studying science? Most of the technical questions asked on the 
lists I read could (and should) be answered by actually studying those 
textbooks. Much of what I read on email lists is the opinions and old wives 
tales of those who haven't, and much of it is wrong. 

My tutorial is at http://audiosystemsgroup.com/RFI-Ham.pdf  In addition to 
teaching most fundamental concepts relating to RFI and ham radio, it includes 
a presentation of what I've learned about ferrite chokes for suppression, and 
a lot of MEASURED data. 

73,

Jim Brown K9YC