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Hi Stefan,
guess it depends on what you want to
achieve. Your signal strength is above average, and some dashes have
already been detected several times in Tasmania. You may now be aiming
to convey a complete callsign or a message. Considering
that an opening will often last less than an hour, DFCW 600 may
already be too slow for this purpose. Although, as Paul
Nicholson recently pointed out, visual QRSS or DFCW may not
be the most efficient schemes in terms of data
throughput at limited SNR.
On the other hand, others with more
limited ERP would probably be very happy with a
simple and unique overseas detection of the presence of their
signal. For this purpose, very long carriers and half-milliHz detection
bandwidth (aka "6000") have proven extremely valuable at
VLF. My point was that such a narrow bandwidth would still be
supported by the stability of an LF long-distance
path.
How different is 100 kHz from 137? I
think that although there may be some differences (eg. less groundwave
absorption and smaller phase variability at lower frequency), the general
behaviour seems quite similar. Although I havent attempted a proper quantitative
analysis, the strength of 100 kHz Loran signals eg from Japan or America seemed
to be fairly well correlated with propagation conditions observed
by LF amateurs or DCF39.
Best 73,
Markus (DF6NM)
Sent: Friday, September 26, 2014 2:37 PM
Subject: Re: LF: European Loran in Tasmania
Hello Markus, Edgar,
LF,
Does that mean you would recommend to try slower DFCW modes than 180
? Maybe 600, like in the old VLF days?
What could be the difference in
propagartion between 2200m and 3000m ?
73, Stefan
Am 26.09.2014
01:50, schrieb Markus Vester:
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)
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