Dear LF group,
the considerations which led
to the choice of a new Eu waterhole have been explained
in a posting from Dec 12th, attached beneath. Here's a
brief summary of the current situation:
- We clearly need separate
E-W and W-E slots, due to side effects of noise blanking,
and imperfections of transmitters and receivers.
- The Canadian West coast
(Scott, Steve) experiences wide-area interference
(presumably PLC), centered on 135700 and 136320. This is
what triggered the search for an alternative Eu slot.
- Central and Eastern Europe
suffers from HGA22 sidebands, except for a few narrow
slots (135.975, 136.177, 136.38) . The density of FSK
telegrams on DCF39 and HGA22 has been increasing.
- We want to stay far enough
from 137.0 in case CFH would be fired up more regularly.
- But we now have the
problem that Jay is affected by local QRM around
136.177. It consists.predominantly of a group of
unstable lines, spaced by about 1 Hz.
I had secretly hoped that
Jay might ultimately find a way to identify and
fix the problem locally, but this may simply not be
feasible. How far up and down does this interference
extend in frequency? I'm also not sure whether Warren
is actually having the same difficulty or not.
Now we have the dilemma that
if we stay on the new slot, we may loose many excellent
high-quality observations from Jay. If we move back to the
old one, we give away the slim chance of being picked up
by Scott or his friends during that special Transpolar
night.
The best choice may be
to move on again. If we decide so, we will then need to
collect information regarding bad and good channels from
all key players, perhaps by detailed analysis of wav
recordings of the whole lower part of the band.
Best regards,
Markus (DF6NM)
Sent: Sunday, December 12, 2010 3:13 PM
Subject: New Eu slot 136.177 kHz?
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)
