At 09:59 AM 2/13/02 -0500, you wrote:

>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.

The ELF transmitters in northern Russia, Michigan and Wisconsin are
almost *beneath* the audio range (< 100Hz!).

Here's one take on it:-

http://www.provcomm.net/pages/joe/introlf.htm

"The "long wave" spectrums of frequencies are divided into three main
grouping by convention. These are;
LF (Low Frequencies) 535 to 150 kHz
VLF (Very Low Frequencies) 150 kHz to 3 kHz
ELF (Extremely Low Frequencies) 3 kHz to 300 cycles (approx.)"

Best regards,

Spehro Pefhany --"it's the network..."            "The Journey is the reward"
speff@interlog.com             Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog  Info for designers:  http://www.speff.com
9/11 United we Stand

--
http://www.piclist.com hint: The PICList is archived three different
ways.  See http://www.piclist.com/#archives for details.