Hello Stefan!
Thank you, Stefan, for your remarks and your good words. Unfortunately, the
antenna was mounted in a public venue that's why we had to take it down just
after our tests. We wanted to see whether it is possible to work in VLF
using basic equipment. Once the weather conditions are good enough on a
weekend I'll send an antenna mounted to a baloon into the air. I've already
done something similar working on 472kHz.
https://klubnl.pl/wpr/en/index.php/2018/12/16/eksperyment-w-pasmie-630m-z-an
tena-unoszona-za-pomoca-balonu/
Currently I'm building antenna coils on ferrite cores with high AL=12700.
The circuit of the autotransformer has already been tested.
When Jacek has a free weekend, we will be experimenting.
73! Marcin SQ2BXI
-----Original Message-----
From: [email protected]
<[email protected]> On Behalf Of DK7FC
Sent: Monday, March 4, 2019 10:27 AM
To: [email protected]
Subject: Re: VLF: ebnaut transmission from Poland
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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