Yes.  There are "cave" radios operating at very low frequencies and I helped
design a system to receive communications from a downhole tool operating at
very low frequencies.  Already mentioned was the submarines, but some little
known applications involve listening to lightning sprites and earthquakes.
IIRC The earthquake theory is that large piezo electric discharges are given
off as a result of the stresses prior to movement.  There are a whole
variety of sprites that give off wild effects and a number of websites that
contain the sounds. Fascinating stuff.

http://www.elfrad.net/index.htm

-----Original Message-----
From: piclist-bounces@mit.edu [mailto:piclist-bounces@mit.edu]On Behalf
Of Per Linne
Sent: Friday, November 26, 2004 2:24 AM
To: PICLIST
Subject: [EE]5 kHz wireless


A potentional client has approached me. They are in the
physiological niche. They want me to develop a thing to
some equipment they have. I understand that it has to do
with some kind of (human) pulse measurement device. They say
that this equipment communicates wirelessly over 5 kHz!!??
With the risk of making a fool of myself (which I do now and then),
 I ask: I there really such a thing? (5 kHz wireless,  that is.)
I have never seen anything about such a low frequency. Must
be vveerryy long waves!!?? Or have they (or I) misinterpreted
the devices data?

Regards,
Per Linne

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