"Audio is ELF. An audio-frequency circuit still radiates
     electromagnetic waves, just not very efficiently."

 "Very incorrect in all but perhaps a very few ill-designed
 products. Most of us responsible for actual RF design
 don't call possible 'spuriuous emissions of AF energy' over
 100 dB down from a 'box' "radiation of electromagnetic
 waves". Leakage flux perhaps (as from a power xfmr) - but
 not 'radiation'.

 I realize I'm addressing a majority digi-head crowd - some
 of this discussion is only underscoring that point.

 No offense meant to any digi-head on the list. We couldn't
 possibly do what we do in the field of RF today without uC's
 or the talented programmers and designers who actually make
 those devices 'sing' and 'dance' ...

 Jim"

Jim, others:

I'm afraid your not quite correct here Jim; as stated by others, there is no
magic frequency where AF ends and RF begins - it is most definitely blurred.

What is important is Efficiency, as efficiency for each purpose varies with
frequency.

But there definitely are audio frequency "RF" transmitters, and these are
not "ill-designed products." For example, the U.S. Navy uses what most would
consider as "Audio Frequencies" in their equipment designed to communicate
with submerged submarines. Though efficiency is horrendous, the importance
of the task makes the inefficiencies acceptable.

Also, you should not assume that the audience cannot rationally consider the
topic, as many have mixed disciplines. While I probably could not match your
level of expertise, I have been workinging with RF as an amateur (HAM) since
the '70s. I'm sure there are many readers that have even more experience
than I.

Bruce.

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