Hi Jacek, Marcin,
Well done! Congratulations to a first VLF signal coming from SP that is
detected over such a distance, more than 1000 km! This is truely
encouraging and shows what could be done by MANY amateurs, if they would
just give it a try!
A milestone for your country, from an amateur radio view.
Thanks for the details in that website. It is interesting to see that
such ground loop antennas seem to work even in regions where the ground
conductivity is expected to be quite high. Thanks to Paul's decode, you
now have the certainty that the signal actually propagates.
Well, the ground loop seems to radiate into Paul's direction and there
is a lot of water on your path (between you and Paul). Also we (DL0AO
and DK7FC) are closer to QRN sources in south-east Europe. This will
contibute to our negative decode result here.
On the other side we saw that the signal also propagates into unexpected
directions, at least as long as the QRB is lower than 2000 km.
It would be most welcome to see more activity from your side! And it
looks like you can rise the ERP by 10 dB without much effort. Are you
planning more experiments? And when? :-)
The EbNaut message was transmitted during a time where phase changes are
likely, because it was during the sunrise at your location. Maybe you
can repeat the experiment, using 2 characters transmitted over 6 hours,
starting 21 UTC for example? That would help us, here in the south, to
receive your message.
I will have a look at my signal recording to see the SNR for the message
'SP' later.
At 75W and 300V antenna voltage you had 250 mA antenna current and, as
you wrote, 1200 Ohm. If you have 500 Ohm DC resistance then i conclude
that you did not series resonate the antenna. The reactive component was
j1090 Ohm, so a series C of 177 nF (100+47+22 nF) would help to reduce
the feed point impedance to 500 Ohm. Not sure if you could then run a
higher power but at least the PA losses would be a bit lower.
With some cheap 0.75mm2 CCA loudspeaker cable you could reduce the wire
losses by about 90%.
All this is very nice promising!
Good luck and i hope to get a new chance to receive you here soon.
73, Stefan
Am 03.03.2019 19:44, schrieb Jacek Lipkowski:
On Sat, 2 Mar 2019, DK7FC wrote:
I've tried a lot of antenna mixing but did not get better spectrum
peaks that 10.5 dB SNR, so it is quite weak. Best decoder result was
'AV' at rank 70.
The transmitted message was: SP
I'm waiting for your detailed description of the experiment. What
antenna and power was used? How did you generate signal?
A preliminary descritpion is here:
https://klubnl.pl/wpr/en/index.php/2019/03/03/nadawcze-proby-z-dipolem-ziemnym-w-zakresie-vlf/
Around 100W into a 500m long earth dipole, the signal was weak and we
were surprised to have Paul receive it (well, maybe not that surprised
given Paul's excellent receiver).
For the 8270.005Hz carrier we used a GPS generator module (i think it
might be just an uBlox GPS inside, but didn't investigate it). I think
Marcin bought it on some auction site.
For 8270.00073Hz we used an old Neoware terminal with an uBlox neo-7M
GPS installed inside. The gps is used to provide a coarse time
reference (not the best precision because the 1PPS signal is not
used), and as a 20kHz reference signal connected to the terminal sound
card. The terminal runs a slightly modified version of Paul's ebsynth,
and some custom-written software to control the gps. This is the same
generator that i've used in my other tests. I can publish some details
in case anyone is interested.
VY 73
Jacek / SQ5BPF
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