Re: VLF: 300 mA on 6470 Hz

[DK7FC <selberdenken@posteo.de>]

Hi Markus, Paul, VLF,

Thanks for the feedback. The trace at DL0AO looks very good. On 8270 there is almost nothing during daytime but on 6470 we have a stable 10 dB SNR in 424 uHz, allowing a 20 char message in one day!
On Pauls side the SNR is equal, day and night. And on Jacek's QTH the night SNR is much higher than the day SNR. Look at the impressing trace from the last night: https://klubnl.pl/wpr/en/index.php/klubnl-pl-grabbers/grabber-sq5bpf-6470hz/

Now, let's start with a short message with unconventional parameters here in the 46 km band:

f = 6470.005000 Hz
Start time: 04.October.2017  17:00:00 UTC
Symbol period: 90 s
Characters: 1
CRC bits: 0
Coding 16K25A
Duration: 12h
Antenna current: 300 mA

73, Stefan

PS: Paul, i see you changed the EbNaut calculator page again. There is a mode 16K23 which could be interesting for very short messages on a windows PC. However the mode is not available in the ebnaut-tx.exe and in ebnaut-rx.exe.


Am 03.10.2017 21:50, schrieb Markus Vester:

Hi Stefan,

quite a solid signal on the DL0AO grabber!
 http://df6nm.bplaced.net/dl0ao/VLFgrabber/vlfgrabber_dl0ao_test.htm
Despite lower ERP, daytime SNR appears to be much better than on 8270 Hz. This is presumably caused by a) stronger signal due to more favourable ground / skywave phasing at this distance, and b) lower noise due to lower radiated power from limited-length lightning discharges. 

Good luck!
Markus (DF6NM)

-----Ursprüngliche Mitteilung-----
Von: DK7FC <selberdenken@posteo.de>
An: rsgb_lf_group <rsgb_lf_group@blacksheep.org>
Verschickt: Di, 3. Okt 2017 0:29
Betreff: VLF: 300 mA on 6470 Hz

Hi VLF,

Since 22 UTC, a carrier with 300 mA antenna current is running at
6470.005 Hz. The ERP is about 50 uW.
That's the next step in the series of experiments transmitting on
frequencies down to DC :-)

The coil has 3 and 1/2 stacked buckets now. That gives about 1.3 H. It
was necessary to separate the upper and lower two buckets a bit more
than usually, otherwise the frequency was at 6223 Hz. I expect i will
reach 5170 Hz when the spacing is reduced to the normal value (70 mm)
and when i fully wind the upper bucket.

Here's an image of the construction as it was used on 8270 Hz:
http://www.iup.uni-heidelberg.de/schaefer_vlf/VLF/8270_new_coil.jpg The
new construction uses one more of these buckets.
They say there will be strong rain during the whole night. I don't yet
know how this will detune the antenna. Maybe the safety circuit tripps.
But if not, i intend to run the carrier for 24+ hours, so people can
check their grabbers and phase and so on :-)
A first EbNaut message will follow during the week...

73, Stefan


Am 02.10.2017 22:02, schrieb Jacek Lipkowski:
> Stefan, thanks for the carrier, this helped me improve my grabber a bit.
>
> i've changed the time range in my grabber to 7 days, so that you can
> compare with your previous carrier, and also added a "normalised"
> spectrogram:
>
> https://klubnl.pl/wpr/en/index.php/klubnl-pl-grabbers/grabber-4-8270hz/
>
> in the normalised spectrogram the average of relative powers for each
> timeperiod are normalised to a constant value. so this is something
> similar to AGC, taking care of day/night noise variations. i think
> Paul does something similat, because his spectrogram doesn't show
> differences in day/night noisefloor.
>
> the S/N isn't great, but this is from a simple e-field antenna in the
> middle of the city.
>
> i've also added a 6470Hz grabber for your next tests (and will add
> 5170Hz and normalized graphs in the future):
>
> https://klubnl.pl/wpr/en/index.php/klubnl-pl-grabbers/grabber-sq5bpf-6470hz/
>
>
> VY 73
>
> Jacek / SQ5BPF