VLF,
In the event that Paul can produce no decode of my aborted
transmission, i'm announcing a new attempt for the same message, but
this time in shorter daily repetitions that can be added coherently
(like in WOLF mode):
f = 5170.000000 Hz
Start time: 10.Jan.2017 08:00:00 UTC
Symbol period: 24 s
Characters: 20
CRC bits: 16
Coding 8K19A
Duration: 8h, 12m, 48s
Antenna current: ~ 225 mA
73, Stefan
Am 09.01.2017 13:30, schrieb DK7FC:
Unfortunately the transmission has stopped at 11:26 UTC, which is 6h
4min 40s to early. I don't know why :-(. No reason can be found in
SpecLab (no scheduled actions active). The parameter a=0.5 which means
that the transmission is off, so it was stopped by software. But there
is no reason why a was set to 0.5 it this time. I also checked that the
txt file has 2560 symbols. And the symbol length is correctly set to
64s which one can also see on the first sideband minima in the 424 uHz
spectrogram which came a bit closer to +-15 mHz.Very odd! The
transmission should have run until 17:30:40 UTC.
That's a clear disadvantage of such long messages sent into a single
(non-stacked) transmission, if something happens after 70% of the TX
time, everything can be lost.
Paul, maybe the part that was sent until now is already enough to get a
decode? This will be a very hard challenge and i'm not so optimistic :-(
Now its up to you...
73, Stefan
Am 07.01.2017 19:08, schrieb DK7FC:
Thanks Paul (and Renato and Wolf!), very well!
The carrier on 5170.001250 Hz is still on the air and will run until 18
UTC.
Since it appears that you and Jacek are the only ones trying to receive
my EbNaut, i'll stay at 16K25A, just to use the better code gain.
And since the last ~ 24 hour experiment was running so well, let's try
48 hours! Maybe it leads to a 30 0 30 0 phase pattern:
f = 5170.000000 Hz
Start time: 07.Jan.2017 20:00:00 UTC
Symbol length: 64 s
Characters: 20
CRC 16
Coding 16K25A
Duration: 45h, 30m, 40s
Antenna current: ~ 225 mA
The first time i used your calculator
(http://abelian.org/ebnaut/calc.php?sndb=-63&snbws=2500&snmps=&code=16K25&sp=64&crc=16&nc=20&submit=Calculate
) to chosse the number of characters and the symbol length BEFORE the
transmission :-)
With your given RAM, how many characters can you decode in 16K25A? And
how long does the decode process take then?
These 2 day long transmissions mostly failed on 6.47 kHz, or gave poor
results. Stacked single day transmissions were a better choice. For a
50 or 75 character message on 5170 Hz we may have to use the same
technique.
I'm often thinking about the old VLF propagation graphs https://dl.dropboxusercontent.com/u/19882028/VLF/fig_02_25a.png
(what
was the original paper where it comes from?) which make more and more
sense to me! On 5170 Hz we already see a real advantage of lower QRN
relative to 8270 Hz or 6470 Hz. According to the graphs, the optimum
frequency should be arround 4 kHz because the QRN from far away is
attenuated much more whereas the poor propagation on that frequency is
not so much expressed for 'short' (1000 km) distances. And BTW, 4 is a
very nice number, isn't it!? Sooner or later someone has to do
something near 4 kHz! I would be curious to see how this band (e.g.
4270 Hz or 70 km!) behaves. I can imagine that it is the best choice,
even in summer or especially in summer!
When looking on the todays 'wideband' window (the upper one on http://www.iup.uni-heidelberg.de/schaefer_vlf/DK7FC_VLF_Grabber2.html)
we
can
see that we are already diving below the QRN :-)
73, Stefan
Am 07.01.2017 05:09, schrieb Paul Nicholson:
Decoded '73 DK7FC' from Cumiana (Renato Romero, vlf15, 504.6km)
with constant ref phase, Eb/N0 = 0.6, S/N 16.16 dB in 11.8 uHz,
-67dB in 2.5kHz.
Very strong at Bielefeld (Wolf Buescher, vlf6, 303.8km)
Eb/N0 11.6dB, 27.17 dB in 11.8 uHz, -56.1dB in 2.5kHz,
constant reference phase.
Here, improved my decode to 3.9dB when I remembered to use the
-a option which normalises the amplitude by the average noise.
I am not seeing much day/night phase shift at any site. Some
measurements on the carrier will be the next job.
--
Paul Nicholson
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