[Lowfer] Question...
Stewart Nelson
[email protected]
Wed, 31 Dec 2003 22:59:47 -0800
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
<HTML><HEAD>
<META http-equiv=3DContent-Type content=3D"text/html; =
charset=3Diso-8859-1">
<META content=3D"MSHTML 6.00.2800.1170" name=3DGENERATOR>
<BASE href=3D"http://www.scgroup.com/ham/">
<STYLE></STYLE>
</HEAD>
<BODY>
<DIV><FONT size=3D2>Hi Mike, Steve, John and all,</FONT></DIV>
<DIV><FONT size=3D2></FONT> </DIV>
<DIV><FONT size=3D2>Peter Martinez, G3PLX of PSK31 fame, built a LORAN =
propagation=20
monitor.</FONT></DIV>
<DIV><FONT size=3D2>Performance was awesome -- he could usually receive =
stations=20
up to 5000 km</FONT></DIV>
<DIV><FONT size=3D2>during the day, and anywhere in the world at =
night! =20
Unfortunately, the</FONT></DIV>
<DIV><FONT size=3D2>system used a custom front end and a dedicated DSP =
board, so=20
it never</FONT></DIV>
<DIV><FONT size=3D2>became generally popular.</FONT></DIV>
<DIV><FONT size=3D2></FONT> </DIV>
<DIV><FONT size=3D2>I believe that a simple system, using a normal SSB =
receiver=20
and a sound</FONT></DIV>
<DIV><FONT size=3D2>card, would perform only a few dB worse. A =
receiver on=20
the US east coast</FONT></DIV>
<DIV><FONT size=3D2>should typically be able to measure all the USCG and =
NELS=20
stations, and</FONT></DIV>
<DIV><FONT size=3D2>sometimes see signals from halfway around the=20
world. </FONT><FONT size=3D2>The results would</FONT></DIV>
<DIV><FONT size=3D2>be quite interesting, because all stations would be=20
</FONT><FONT size=3D2>simultaneously monitored,</FONT></DIV>
<DIV><FONT size=3D2>and propagation delay and </FONT><FONT =
size=3D2>carrier phase,=20
as well </FONT><FONT size=3D2>as amplitude, can be =
reported.</FONT></DIV>
<DIV><FONT size=3D2></FONT> </DIV>
<DIV><FONT size=3D2>I would be interested in helping to write such a=20
program. I am reasonably</FONT></DIV>
<DIV><FONT size=3D2>informed about LORAN signal characteristics, and can =
program=20
DSP and math</FONT></DIV>
<DIV><FONT size=3D2>routines. However, I'm unable do =
this job=20
myself, having no knowledge of</FONT></DIV>
<DIV><FONT size=3D2>multimedia or GUI programming.</FONT></DIV>
<DIV><FONT size=3D2></FONT> </DIV>
<DIV><FONT size=3D2>Here's how a system might work:</FONT></DIV>
<DIV><FONT size=3D2></FONT> </DIV>
<DIV><FONT size=3D2>Your radio is tuned to e.g. 101.600 kHz LSB. =
Below are=20
two pulse groups</FONT></DIV>
<DIV><FONT size=3D2>recorded in Reno, NV. The strong pulses are =
from Fallon=20
(master); the weaker</FONT></DIV>
<DIV><FONT size=3D2>ones </FONT><FONT size=3D2>are Middletown. =
George and=20
Searchlight are buried in the noise, because</FONT></DIV>
<DIV><FONT size=3D2>I was using a loop E-W. </FONT></DIV>
<DIV><FONT size=3D2></FONT> </DIV>
<DIV><FONT size=3D2></FONT> </DIV>
<DIV><FONT size=3D2></FONT> </DIV>
<DIV><=49mg alt=3D"" hspace=3D0 =
src=3D"loran1.gif"=20
align=3Dbaseline border=3D0></DIV>
<DIV><FONT size=3D2></FONT> </DIV>
<DIV><FONT size=3D2>Each pulse group appears almost as a noise burst, =
with no=20
apparent similarity</FONT></DIV>
<DIV><FONT size=3D2>from one to the next. However, they can be =
coherently=20
demodulated. In the</FONT></DIV>
<DIV><FONT size=3D2>image below, the data was mixed with a sine wave at =
1640.7 Hz=20
(my receiver is</FONT></DIV>
<DIV><FONT size=3D2>almost 10 Hz off frequency), and filtered =
through a 1500=20
Hz lowpass. </FONT></DIV>
<DIV><FONT size=3D2></FONT> </DIV>
<DIV><FONT size=3D2><=49mg alt=3D"" hspace=3D0=20
src=3D"loran2.gif" align=3Dbaseline=20
border=3D0></FONT></DIV>
<DIV><FONT size=3D2></FONT> </DIV>
<DIV><FONT size=3D2>This now looks much like the original LORAN baseband =
signal. On Group A, a master</FONT></DIV>
<DIV><FONT size=3D2>sends ++--+-+- + and a secondary =
sends +++++--+=20
. For group B, the signals are</FONT></DIV>
<DIV><FONT size=3D2>+--+++++ - (master) and +-+-++-- (secondary). =
On these=20
strong signals, this data</FONT></DIV>
<DIV><FONT size=3D2>is clearly visible in individual pulses. =
Distant=20
stations are seen by summing</FONT></DIV>
<DIV><FONT size=3D2>many pulses. For example, if =
measurements are=20
made every 15 minutes, more</FONT></DIV>
<DIV><FONT size=3D2>than 75,000 </FONT><FONT size=3D2>pulses per station =
can be=20
averaged.</FONT></DIV>
<DIV><FONT size=3D2></FONT> </DIV>
<DIV><FONT size=3D2>Software PLLs would lock to the frequency and pulse =
rate of a=20
"reference"</FONT></DIV>
<DIV><FONT size=3D2>station, typically the one nearest to the =
receiver. =20
LORAN pulses are synchronized</FONT></DIV>
<DIV><FONT size=3D2>to </FONT><FONT size=3D2>UTC. Conceptually, =
all master=20
stations sent their first pulse on 1/1/1958 at</FONT></DIV>
<DIV><FONT size=3D2>00:00:00. By examining the timing of a nearby =
dual-rated=20
station, it's</FONT></DIV>
<DIV><FONT size=3D2>possible to correct for a few seconds of error in =
the PC=20
clock, and sync the</FONT></DIV>
<DIV><FONT size=3D2>software to UTC. Then, the expected time of =
arrival of=20
pulses from any</FONT></DIV>
<DIV><FONT size=3D2>station can be calculated, allowing positive ID, =
even if other=20
stations in that</FONT></DIV>
<DIV><FONT size=3D2>chain cannot be received. This also permits =
display of=20
ionospheric delay.</FONT></DIV>
<DIV><FONT size=3D2></FONT> </DIV>
<DIV><FONT size=3D2>Lots of details have been omitted; I'd be glad to =
supply them=20
if anyone cares :)</FONT></DIV>
<DIV><FONT size=3D2></FONT> </DIV>
<DIV><FONT size=3D2>73,</FONT></DIV>
<DIV><FONT size=3D2></FONT> </DIV>
<DIV><FONT size=3D2>Stewart KK7KA</FONT></DIV>
<DIV><FONT size=3D2></FONT> </DIV>
<DIV><FONT size=3D2>----- Original Message ----- </FONT>
<DIV><FONT size=3D2>From: "Steve Dove" <</FONT><A=20
href=3D"mailto:[email protected]"><FONT =
size=3D2>[email protected]</FONT></A><FONT=20
size=3D2>></FONT></DIV>
<DIV><FONT size=3D2>To: <</FONT><A =
href=3D"mailto:[email protected]"><FONT=20
size=3D2>[email protected]</FONT></A><FONT =
size=3D2>></FONT></DIV>
<DIV><FONT size=3D2>Sent: Tuesday, December 30, 2003 7:03 =
PM</FONT></DIV>
<DIV><FONT size=3D2>Subject: Re: [Lowfer] Question...</FONT></DIV></DIV>
<DIV><FONT size=3D2><BR></FONT></DIV><FONT size=3D2>> Hi John, =
Mike,<BR>>=20
<BR>> Yes, the lines are a composite of the differing sites; =
maybe a=20
crossed-loop <BR>> differential technique such as Marcus DF2NM and =
Wolf=20
DL4YHF developed - <BR>> whereby signals from different=20
directions get displayed as different colours on the <BR>> plot =
- could=20
help sort out what Loran components are instantaneously <BR>>=20
significant.<BR>> <BR>> Could also be groovily =
psychedelic.<BR>>=20
<BR>> Cheers,<BR>> =
<BR>>=20
&=
nbsp; =20
Steve<BR>> <BR>> <BR>> 12/31/2003 1:12:59 AM, "John Davis"=20
<</FONT><A href=3D"mailto:[email protected]"><FONT=20
size=3D2>[email protected]</FONT></A><FONT size=3D2>> =
wrote:<BR>>=20
<BR>> >As I recall, this was one of the possible purposes John =
Andrews=20
mentioned in<BR>> >connection with his list of LORAN lines, and =
why each=20
line is identified by<BR>> >its associated chain on that =
page. Since=20
each site in a chain contributes<BR>> >to a given line, its =
strength=20
signifies propagation quality only in a very<BR>> >broad general=20
direction. A chain that encompasses the receiving site =
would<BR>>=20
>thus be less helpful than a chain farther away, for =
instance.<BR>>=20
><BR>> >We see the occasional reports here that LORAN lines in =
general=20
seem strong<BR>> >or not on a given occasion. But I think =
it's an=20
idea that hasn't been<BR>> >adequately explored on a systematic =
basis=20
yet.<BR>> ><BR>> >John<BR>> ><BR>> ><BR>>=20
>-----Original Message-----<BR>> >From: Mike Staines =
<</FONT><A=20
href=3D"mailto:[email protected]"><FONT=20
size=3D2>[email protected]</FONT></A><FONT size=3D2>><BR>> =
>To: Lowfer=20
<</FONT><A href=3D"mailto:[email protected]"><FONT=20
size=3D2>[email protected]</FONT></A><FONT size=3D2>><BR>> =
>Date:=20
Tuesday, December 30, 2003 7:15 PM<BR>> >Subject: [Lowfer]=20
Question...<BR>> ><BR>> ><BR>> >>Has anyone ever=20
considered/studied/used Loran lines as a predictor of<BR>>=20
>>propagation conditions?<BR>> >><BR>> >>Now =
that I have=20
a fairly decent RX setup here at the winter HQ, I have<BR>> =
>begun<BR>>=20
>>to notice that the fade patterns of some beacons coincide with=20
the<BR>> >>appearance/disappearance of loran lines. I am =
wondering if=20
we could predict<BR>> >>propagation based upon the loran lines =
we are=20
seeing at any given time.<BR>> >><BR>> >>Am I =
reinventing the=20
wheel (as I often do) ?<BR>> >><BR>> >>Mike<BR>>=20
>>wm1ke<BR></FONT></BODY></HTML>
--- StripMime Report -- processed MIME parts ---
multipart/alternative
text/html
text/plain (text body -- kept)
The reason this message is shown is because the post was in HTML
or had an attachment. Attachments are not allowed. To learn how
to post in Plain-Text go to: http://www.expita.com/nomime.html ---