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Dear LF,
after considerations with
Scott VE7TIL, Mike G3XDV, and Laurence KL7UK, I would like
to discuss moving the European intercontinental transmit slot. It
is currently centered on 136.320 kHz, and I propose a new center
frequency of 136.177 kHz.
This discussion was initiated by VE7TIL,
who is plagued by severe QRM lines, to an amount that he considers the
vicinity of 136.32 kHz as being unusable for him. Scott believes
that the interference is caused by a PLC system leaking from a
nearby powerline, and that it will probably not be possible to fix it
locally. Of course it can be disputed whether QRM
at one receive site would be reason enough to change a band plan, which has
been useful for a number of years. On the other hand, there is only a
limited number of receivers around the world. And we would certainly
like to have Scott onboard, as the path from Eu to the American West coast is
certainly one of the most challenging ones.
A few years ago, we decided to move Eu
transmissions from the original 135922 Hz to 136320 Hz, driven by a
wider gap in the American Loran-C line spectrum. Since the shutdown of US and
Canadian Loran chains, this is no longer an issue.
One benefit of going back to a lower frequency
would be moving further away from the Canadian military transmitter CFH, which
occasionally sends out a strong FSK (or MSK) signal centered on 137.0 kHz. It
would be interesting to get some information how much this one actually
affects the American LF background at different frequency offsets.
Here in Europe and Russia, a possible
disadvantage of going down is that we would also come closer to HGA22. This is
the 100 kW telecontrol transmitter in Budapest, an idle carrier sitting at
135.43 kHz, and excursions to 135.77 during FSK bursts. Normally these
bursts appear every 11 seconds, but at times there are annoying blocks of
consecutive telegrams several minutes long. Here in Bavaria, the FSK
modulation sidebands are visibe up to about 136.5 kHz, but there are
pronounced spectral gaps due to the 200 bd modulation. These clear gaps
are near 135.97, 136.17 and 136.37 kHz.
We looked at 136.37 first, but this would
not fix the problem for Scott. 135.97 seems worse in Europe due to Luxembourg
effect impressed on HGA, and is also getting close to the Greek military SXV. So
we decided to focus on 136.17 kHz. A
closer look revealed that this very useful FSK
minimum is actually centered on 136177 Hz, and about 8 Hz
wide.
For the last few days, I have been running my
grabber http://www.alice-dsl.net/df6nm/grabber/Grabber.htm
with a split window, showing both the present and the proposed new slot
side by side. The direct modulation sidebands (showing as red bands) are
much better on the new frequency. Nighttime Luxembourg QRM generally does
not appear to be worse, despite being closer to the HGA
carrier. We also expect the latter to be a more regionally
confined effect, which will not be present in remote areas of the
world. After all, the main purpose of Eu-slot grabbers within Euroupe would
not so much be ultimate sensitivity, but rather to provide a monitor for
intra-Eu transmit frequency coordination, and a comparison log for verification
of DX receptions.
Before coming to a possible decision to move the Eu frequency band, we
would like to collect some feedback on the receive situation in different parts
of the world. Traditionally, Eu slot transmissions were primarily targeted
towards the American east coast. But of course we would like
to include other areas of the world. How useful would the proposed
slot be for example in Russia or Japan?
Active Loran-C rates in Japan are GRI 8930 (lines at 136175.812 and
1368181.411 Hz) and GRI 9930 (lines at 136173.212 and 136178.248 Hz).
Russia uses GRI 8000 with lines at 6.25 Hz multiples, and perhaps GRI
7950 (136178.157 Hz). As the frequencies are very accurate, these lines
are very useful calibration markers.
Now, your opinions please!
Best regards,
Markus (DF6NM)
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