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Message-ID: <65AECDF1F89AD411900400508BFC869F9C0405@pdw-mail-1.dera.gov.uk>
From: "Talbot Andrew" <ACTALBOT@dera.gov.uk>
To: "LF Group \(E-mail\)" <rsgb_lf_group@blacksheep.org>
Subject: LF: LF Propagation Monitoring using LORAN
Date: Mon, 26 Mar 2001 11:43:47 +0100
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A couple of weeks ago there was discussion on this reflector about using
LORAN as a source of LF propagation information.  I forwarded these on
to Perter, G3PLX, who looked at LOARN for this purpose some time ago.
Here are the two responses received from him :

Andy  G4JNT
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------------------
Thanks for the LORAN information. I had, as you will remember in the
days I was active on LF, done the LORAN software and was seeing most
of the phenomena quoted. If you remember, I was able to integrate the
energy received over the 136 kHz band and show that ALL the LORAN
transmitters audible on 100kHz were also emitting crap on 136kHz. I
must have another look, especially for the dx signals, about which I
had no chain GRI data. Looking for individual spectral lines is not
at all a good way to detect distant LORAN, since the amount of power
in one spectral line is a very small proportion of the total signal
power. It's rather better to receive the full bandwidth coherently at
100kHz, integrating the I and Q signals in an array of "time bins" at
the group repetition rate, and watch the narrow sqrt(sqr(I)+sqr(Q)
pulses creep out of the noise as time goes by.
---------------------------------------------------------------------

-----Original Message-----
From: Peter Martinez [mailto:Peter.Martinez@btinternet.com]
Sent: 2001-03-25 20:09
To: Talbot Andrew
Subject: Re: LF Propagation Monitoring 

Andy:

I dug out the LORAN software and had another play with it, and also
visited the Megapulse site to get a copy of the table mentioned by
one of your correspondents. As a result I have been able to identify
all the signals he was hearing, including some of the Newfoundland
sites, the West Russian one and the Saudi chain. I am doing this by
listening in a 3 kHz band straddling 100kHz and coherently
demodulating and integrating I/Q over several minutes at the chosen
group repetition rate.

I have also started writing a program to streamline this activity. It
isn't finsihed yet but will be able to derive frequency and time
references from one transmitter (for example Lessay) and use this to
attempt to coherently demodulate and synchronously detect other
signals, although I probably won't use the fascinating fact that all
LORAN transmitters emitted their first pulses at midnight on
01/01/1958 to get the timing absolute. Such a program could be
written for a soundcard/PC combination and would just need a
receiver, preferably the full LORAN bandwidth, tuned to make 100kHz
appear in the centre of the sampled audio band. At the moment I am
running it on my old DSP card and I don't think I could make it run
on the EVM because the front-end processing requires rather more data
fed to the PC than I can squeeze down the serial port.

73
Peter


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