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 The material in the ARRL Handbook is woefully out of date and quite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I'm not sure if "out of date" is exactly right in this context (neither the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
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