Mal, LF,
Am 02.08.2011 22:49, schrieb Chris Trayner:
Perhaps some of the grabber operators would like to reply with their hints and
kinks - personally I'm ignorant of how they run these things.
73,
Chris G4OKW
First we should keep in mind that it is summer! And summer in EU is a
different thing than summer in UK. If you take a look at
http://www.blitzortung.org/Webpages/index.php?lang=en&page=1 from time
to time, you will see what i mean. So, receiving in UK is easier than
here, often.
Furthermore the grabber runners HAVE TO run a PC while operating but the
CW amateur could shut down the complete house if the RX runs on
batteries, if necessary.
And: LF is a never ending project of improvements and optimisations.
Everything could be made a bit better, on the RX and TX and antenna
side. This also applies to my LF grabber. It was improved before some
months by fine adjusting the filters, changing the probe location and
adding a bandpass in front of the first gate. This has improved things
strongly but anyway i saw some IM of DLF (153 kHz) that modulates with
DCF39.
This is a further thing: In Germany we have DCF39, DLF (153 kHz) and
DCF49 (129 kHz). The sidebands of DCF39 are often visible in the 137.7
kHz range, even when using a noiseblanker. DLF runs 500 kW to a 350m
tower and is in 40km distance here....
I will investigate what to improve further on the front end. But a
recent test with G3XIZ showed that my single turn RX loop (that performs
excellent) was not better.
And the TX antenna is worse in every way. It is in parallel to the tram
line which is in 100m distance
Mal, this week, maybe tomorrow i will try to realise the 70cm link and
then try from a remote location. I hope you'll have the PA ready for
full power? We are still in summer, so a few dB more might help too. BTW
i see my signal almost every day on the G4WGT grabber.
Ah, Mal, another thing: Propagation! It is possible that you're 30 dB
S/N and 10 minutes later you're lost in the noise and then come back
later. So, if you look to the wrong time, you'll see nothing. We all
have to live with that instabilities but this makes LF something
interesting and special.
73, CU, Stefan/DK7FC
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