Last night, Edgar J. Twining in Moonah, Tasmania has
successfully picked up several Loran-C signals from the other side of
the world. He was using an E-field antenna connected to his Excalibur
receiver, tuned to a 6 kHz band around 100 kHz. For phase and timing
reference, the rising edge of 1pps pulses from a GPS device was
capacitively injected to the antenna line. In the wee hours between 18
and 19:50 UT, Edgar produced a set of four 20-minute recordings,
which were then postprocessed here using my homebrew "LoranView"
averaging software.
Attached image is the result using one-minute averaging. Each of
the 40 columns corresponds to the repetition rate and delay of a single
Loran station, dual rated stations appear twice. The order of slots is
generally west to east, with the exception of the GRI 7950 chain at the
right which has been added later. Horizontal timescale within each slot
is equivalent to the 12 kHz samplerate, ie. 83 us per pixel or 2 ms in
each slot. Vertical scale is one pixel per minute, from 18 (bottom)
to 19:50 UT (top), with three 11 minute interruptions due to the gaps
between files. Colour hue corresponds to received carrier phase,
referenced to the 1pps pulse shown in the leftmost slot. The slots for
the Chinese navigation stations are empty as these have been off air
for a couple of days, presumably for maintenance.
Edgar's is getting solid traces even from his furthest station,
Lessay at 17521 km, which is radiating 250 kW peak or about 3 kW
average power on each of the two rates. As all Loran stations share a
common frequency band, the fact that he doesn't have nearby stations
probably helps to reduce crossrate clutter, allowing him to fully
exploit the sensitivity of his excellent receive setup.
Interestingly, the colour of the very distant traces is changing
only slowly, indicating phase stability of the path on the order of an
hour or so. This confirms that sub-milliHz bandwidths can
indeed be useful to enhance slow weak-signal communication on 137 kHz.
Best 73,
Markus (DF6NM)
Hi Edgar,
it's
getting better and better... see attached result from this night!
Between
18 and 20 UT, Lessay has become really strong, and the other Europeans
are making their appearances. It looks like you've almost achieved what
I would call a "Loran Marathon", which (in analogy to hobby
astronomer's "Messier Marathon") would be seeing traces from all active
Loran stations during the course of a single night. The leftmost (ie
most north-westerly) stations are probably the most difficult ones
because there is little common darkness, and the path goes through the
northern auroral zone. You are definitely seeing Ejde and Bo, only Jan
Mayen is not quite there yet.
Thanks
to your data, I was able to measure the time offset for the Russian Far
East chain, GRI 7950. Some Russian "Chayka" chains occasionally change
their absolute timing in an unpredictable manner. I had lost this one a
couple of years ago and wasn't able to find it again from here. I have
now appended it also to my own monitor, hoping to see traces tonight. I
have also corrected an offset to show Ash Shayk 8830Y, wheras Al
Muwassam 8830Z is currently really off air.
I still have to write up some details about the software. I want to
make a couple of changes to make the timing and synchronisation a
little more reliable, and intend to send a hopefully working version to
you this weekend.
Best
73,
Markus
