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Re: VLF: Back on 5.17 kHz / 58 km...

To: [email protected]
Subject: Re: VLF: Back on 5.17 kHz / 58 km...
From: DK7FC <[email protected]>
Date: Mon, 09 Jan 2017 21:34:04 +0100
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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 ( ) 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 (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 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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