Hello LFers !
I centred the European window of my grabber on 136.177 Khz .
If you decide to change another time , I will follow you !
73 Jean-Pierre f1afj
Le 12/12/2010 15:13, Markus Vester a écrit :
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)
|
