Hi Markus, VLF,
Thanks for the information. Yes, something must be strange.
Look on my results/attachments.
I generated a local decode from the tree, of course with a big SNR. But
the phase! I got no better result than 0 0 0 0 (phase pattern), as
expected. Your tool telles there is no frequency offset and just a
small timing offset.
Is this instable phase from the transmitter or the receiver site? Maybe
some components in the loop preamp? Hard to imagine.
Additionally i took a recording on the Raspi, using the setting as for
the ULF experiments, i.e. 24 kS/s sample rate. Unfortunately today i
shut down the Raspi before stopping the recording process. This
corrupted the file. So i will repeat the experiment another time,
today, same start time and parameters.
Yesterday it was warm and sunny, today it is overcast and rainy. If the
phase change is genuine and if it has to do with temperure changes, we
may see a difference in the next decode.
73, Stefan
Am 06.06.2017 13:55, schrieb Markus Vester:
Hi
Stefan,
your message was decoded well from DL0AO cardioid data.
Initially, the best decode appeared with a phase slope, -30 0 0 30.
Entering a frequency offset of one FFT bin (+9.3 uHz), the blue peak
seems to be shifted slightly to the left as expected, but the same best
decode was achieved with flat phase.
This seems to confirm your earlier observation of a one bin offset.
This is strange, as I've never observed such an offset in earlier
experiments based on shorter data with wider FFT resolution (31 uHz or
more), and I am lacking an explanation. I don't think we can blame
propagation because if there was any Doppler around sunset
this should be negative rather than positive.
Best 73,
Markus (DF6NM)
Hi VLF,
For some local tests i like to transmit the 2 character message that i
already sent on 970 Hz 3 weeks ago. This time on 6470 Hz....
Such a short message with sch long symbols may be interesting for
newcomers or various tests by the established VLF receivers...
f = 6470.100000 Hz
Start time: 05.Jun.2017 13:00:00 UTC
Symbol period: 60 s
Characters: 2
CRC bits: 3
Coding 16K21A
Duration: 9h, 20min
Antenna current: ~ 460 mA
73, Stefan
|
rawsyms.png
Description: PNG image
|
