[Lowfer] Question...
Mike Staines
[email protected]
Thu, 1 Jan 2004 19:34:07 -0500
Stewart:
Thanks for the analysis.
I'm going to have to put your note on the back burner until next week but
please believe I do think that this a good project!
73,
Mike
-----Original Message-----
From: [email protected] [mailto:[email protected]]On
Behalf Of Stewart Nelson
Sent: Thursday, January 01, 2004 2:00 AM
To: [email protected]
Subject: Re: [Lowfer] Question...
Hi Mike, Steve, John and all,
Peter Martinez, G3PLX of PSK31 fame, built a LORAN propagation monitor.
Performance was awesome -- he could usually receive stations up to 5000 km
during the day, and anywhere in the world at night! Unfortunately, the
system used a custom front end and a dedicated DSP board, so it never
became generally popular.
I believe that a simple system, using a normal SSB receiver and a sound
card, would perform only a few dB worse. A receiver on the US east coast
should typically be able to measure all the USCG and NELS stations, and
sometimes see signals from halfway around the world. The results would
be quite interesting, because all stations would be simultaneously
monitored,
and propagation delay and carrier phase, as well as amplitude, can be
reported.
I would be interested in helping to write such a program. I am reasonably
informed about LORAN signal characteristics, and can program DSP and math
routines. However, I'm unable do this job myself, having no knowledge of
multimedia or GUI programming.
Here's how a system might work:
Your radio is tuned to e.g. 101.600 kHz LSB. Below are two pulse groups
recorded in Reno, NV. The strong pulses are from Fallon (master); the
weaker
ones are Middletown. George and Searchlight are buried in the noise,
because
I was using a loop E-W.
Each pulse group appears almost as a noise burst, with no apparent
similarity
from one to the next. However, they can be coherently demodulated. In
the
image below, the data was mixed with a sine wave at 1640.7 Hz (my receiver
is
almost 10 Hz off frequency), and filtered through a 1500 Hz lowpass.
This now looks much like the original LORAN baseband signal. On Group A,
a master
sends ++--+-+- + and a secondary sends +++++--+ . For group B, the
signals are
+--+++++ - (master) and +-+-++-- (secondary). On these strong signals,
this data
is clearly visible in individual pulses. Distant stations are seen by
summing
many pulses. For example, if measurements are made every 15 minutes, more
than 75,000 pulses per station can be averaged.
Software PLLs would lock to the frequency and pulse rate of a "reference"
station, typically the one nearest to the receiver. LORAN pulses are
synchronized
to UTC. Conceptually, all master stations sent their first pulse on
1/1/1958 at
00:00:00. By examining the timing of a nearby dual-rated station, it's
possible to correct for a few seconds of error in the PC clock, and sync
the
software to UTC. Then, the expected time of arrival of pulses from any
station can be calculated, allowing positive ID, even if other stations in
that
chain cannot be received. This also permits display of ionospheric delay.
Lots of details have been omitted; I'd be glad to supply them if anyone
cares :)
73,
Stewart KK7KA
----- Original Message -----
From: "Steve Dove" <[email protected]>
To: <[email protected]>
Sent: Tuesday, December 30, 2003 7:03 PM
Subject: Re: [Lowfer] Question...
> Hi John, Mike,
>
> Yes, the lines are a composite of the differing sites; maybe a
crossed-loop
> differential technique such as Marcus DF2NM and Wolf DL4YHF developed -
> whereby signals from different directions get displayed as different
colours on the
> plot - could help sort out what Loran components are instantaneously
> significant.
>
> Could also be groovily psychedelic.
>
> Cheers,
>
> Steve
>
>
> 12/31/2003 1:12:59 AM, "John Davis" <[email protected]> wrote:
>
> >As I recall, this was one of the possible purposes John Andrews
mentioned in
> >connection with his list of LORAN lines, and why each line is
identified by
> >its associated chain on that page. Since each site in a chain
contributes
> >to a given line, its strength signifies propagation quality only in a
very
> >broad general direction. A chain that encompasses the receiving site
would
> >thus be less helpful than a chain farther away, for instance.
> >
> >We see the occasional reports here that LORAN lines in general seem
strong
> >or not on a given occasion. But I think it's an idea that hasn't been
> >adequately explored on a systematic basis yet.
> >
> >John
> >
> >
> >-----Original Message-----
> >From: Mike Staines <[email protected]>
> >To: Lowfer <[email protected]>
> >Date: Tuesday, December 30, 2003 7:15 PM
> >Subject: [Lowfer] Question...
> >
> >
> >>Has anyone ever considered/studied/used Loran lines as a predictor of
> >>propagation conditions?
> >>
> >>Now that I have a fairly decent RX setup here at the winter HQ, I have
> >begun
> >>to notice that the fade patterns of some beacons coincide with the
> >>appearance/disappearance of loran lines. I am wondering if we could
predict
> >>propagation based upon the loran lines we are seeing at any given
time.
> >>
> >>Am I reinventing the wheel (as I often do) ?
> >>
> >>Mike
> >>wm1ke
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