Submariners, Loran C question
 

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?

On Fri, 30 Jan 2004 02:05:19 -0000, (gudmundur)
wrote:

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.

Paul

"Paul Keinanen" wrote in message
...
On Fri, 30 Jan 2004 02:05:19 -0000, (gudmundur)
wrote:

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.

Paul


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.

So that's the freq! For the life of me, I got zillions of hits, but none
talked about the frequency. I only remember the old 1.8 MHz. (or whatever)
Loran system.

--
Steve N, K,9;d, c. i My email has no u's.

"gudmundur" wrote in message
...
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?

"J. Michael Milner" ) writes:
"Paul Keinanen" wrote in message
...
On Fri, 30 Jan 2004 02:05:19 -0000, (gudmundur)
wrote:

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.

Paul


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.


Depth of the boat doesn't matter. The antenna floats near the surface.

In article ,
says...

So that's the freq! For the life of me, I got zillions of hits, but none
talked about the frequency. I only remember the old 1.8 MHz. (or whatever)
Loran system.

--
Steve N, K,9;d, c. i My email has no u's.


Hey there Steve, and the group,

If you want some good reading on the operation of the 100khz Loran-C,
download the manual for the rayplot 700L from Raymarine.com They cover
the 'How it works' department real well. No schematics however. I have
a small battery operated scuba tow unit good for bay, or lake use. It has
no compass due to the very large motor magnets. I was thinking of building
my small portable Loran-C receiver into a waterproof box, and towing an
insulated antenna wire of perhaps 10 feet length behind me. But I was unsure
how deep I could dive, and still have a useable signal. I have a 700L for
land use in my mobile. It works great!






"gudmundur" wrote in message
...
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?

On Sun, 01 Feb 2004 01:33:02 -0000, (gudmundur)
wrote:

I was thinking of building
my small portable Loran-C receiver into a waterproof box, and towing an
insulated antenna wire of perhaps 10 feet length behind me.

You should include a low noise preamplifier in front of the receiver.
Due to the very high atmospheric noise levels on LF and MF bands, the
sensitivity for a typical receiver is very low (especially if a
ferrite rod antenna is used).

Below the surface, both the level of the wanted signal as well as the
atmospheric noise level will drop rapidly and sooner or later the
signal will be swamped by the receiver internal noise (high F figure).
A low noise preamplifier between the antenna and the receiver will
allow a weaker signal to be detected before being swamped by the
preamplifier internal noise when going deeper.

However, if the preamplifier is used close to the surface, it most
likely will overload the receiver, so a pressure switch should switch
out the preamplifier when you are (say less than 3-5 m from the
surface) on include the preamplifier into the receiver AGC loop.

Paul

Paul Keinanen wrote:

On Sun, 01 Feb 2004 01:33:02 -0000, (gudmundur)
wrote:



I was thinking of building
my small portable Loran-C receiver into a waterproof box, and towing an
insulated antenna wire of perhaps 10 feet length behind me.



You should include a low noise preamplifier in front of the receiver.
Due to the very high atmospheric noise levels on LF and MF bands, the
sensitivity for a typical receiver is very low (especially if a
ferrite rod antenna is used).

Below the surface, both the level of the wanted signal as well as the
atmospheric noise level will drop rapidly and sooner or later the
signal will be swamped by the receiver internal noise (high F figure).
A low noise preamplifier between the antenna and the receiver will
allow a weaker signal to be detected before being swamped by the
preamplifier internal noise when going deeper.

However, if the preamplifier is used close to the surface, it most
likely will overload the receiver, so a pressure switch should switch
out the preamplifier when you are (say less than 3-5 m from the
surface) on include the preamplifier into the receiver AGC loop.

Paul



In the case of a LORAN receiver, over load is not a serious matter. The
receiver only has to decide
if a signal is there or not. The LORAN is a pulsed signal and you only
have to detect timing of the pulses.
If the receiver limits strong signals and does not lose sensitivity you
should be OK

Good luck
Bill K7NOM

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.

--

-- //Steve//

Steve Silverwood, KB6OJS
Fountain Valley, CA
Email:

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

In the case of a LORAN receiver, over load is not a serious matter. The
receiver only has to decide
if a signal is there or not. The LORAN is a pulsed signal and you only
have to detect timing of the pulses.
If the receiver limits strong signals and does not lose sensitivity you
should be OK
==============================
Strong sigs can be limited simply by connecting 2 diodes (cross polarity)
across input of receiver.
Using general purpose Si-diodes limits V(peak) to approx 700 mV ,Schottky
diodes to approx 300 mV.

Frank GM0CSZ / KN6WH