On Sun, 1 Feb 2004 12:13:40 -0800, Steve Silverwood
wrote:

In article ,
says...
Is the 100khz Loran C signal useable while submerged? Do to it's
long wave nature, does it penetrate the surface to any depth beyond
a few feet?

Losses are about 10 dB/m at 100 kHz.

The U.S. uses VLH to "communicate with submerged submarines on at
frequencies of 3-30 kHz" (http://www.fas.org/nuke/guide/usa/c3i/vlf.htm).
The data rate is 50 baud but it must work - there are Trident ballistic
missile subs waiting for launch orders on the receiving end.
The depth and receiver characteristics are likely classified.

The way it usually works is to send a three-letter group via VERY slow
CW on a VLF frequency, either via the land-based VLF stations or the
TACAMO aircraft (streaming a way-long wire antenna in flight). This
alerts the intended recipient to near the surface to raise the antenna,
or to float the buoy antenna, and pick up traffic via satellite burst
transmission.


For the stuff down in the power frequency range (under 100 Hz, not 100
KHZ) where the "bell ringer" systems operate, apparently SQUID (super
conducting quantum interference devices) antennas are used. See, e.g.,
http://techreports.larc.nasa.gov/ltr...3-tm212647.pdf

These SQUID antennas work up to a maximum of 1 KHz, so it's not going
to play for LORAN C.

Jack K8ZOA