Re: VLF: Transatlantic success East to West

[Markus Vester <markusvester@aol.com>]

Hi Stefan,

why give up? At -2.5 dB EbN0, Mike and Paul already had about 65% of the required energy for three characters. That's about 2 out of 3, or one character's worth left to do. Now throwing that away and starting afresh, you'll have to do twice the work....     

One could also send a reference carrier to enable phase alignment before stacking, without "cheating" by using known message content, One practical way would be to unbalance the PSK by reducing the shift from +-90° to e.g. +-60°, which would spend 25% of the transmitted energy for a -6 dB reference carrier.

Best 73,
Markus
  

-----Ursprüngliche Mitteilung-----
Von: DK7FC <selberdenken@posteo.de>
An: rsgb_lf_group <rsgb_lf_group@blacksheep.org>
Verschickt: Mo, 18. Dez 2017 21:06
Betreff: Re: VLF: Transatlantic success East to West

Thanks Paul for the summary.

Well, 8 days already and it gets worse. I think the phase changes are not from my side, so it must be the path.
I think i will give up now with this 3 character message. But even a failed attempt gives us a set of data showing the difficulties and phase variations.

On the other side, a single character message is to short to let it be as it is. So i'm trying a new message with just 2 characters before going down to 5170 Hz.
If possible, i daily feedback is apprechated.

f = 17470.1000 Hz
Start time: 18.Dec.2017  21:30:00 UTC
Symbol period: 45 s
Characters: 2
CRC bits: 14
Coding 16K21A
Duration: 09:12 [hh:mm]
Antenna current: 1.2 A

73, Stefan



Am 18.12.2017 18:56, schrieb Paul Nicholson:

Results from eight overnight transmissions of the
3 character message:

 2017-12-10/11  Eb/N0 = -13.1 dB
 2017-12-11/12  Eb/N0 =  -6.3 dB, phase 125.3
 2017-12-12/13  Eb/N0 =  -6.8 dB, phase 143.2
 2017-12-13/14  Eb/N0 = -19.6 dB (stopped 03:40 by safety limit)
 2017-12-14/15  Eb/N0 =  -6.0 dB, phase 68.8
 2017-12-15/16  Eb/N0 = -11.0 dB
 2017-12-16/17  Eb/N0 = -14.6 dB
 2017-12-17/18  Eb/N0 =  -9.9 dB, phase 37.0 (stopped 04:19 by snow)

Stacking

 11/12 + 12/13 gives Eb/N0 = -3.6 dB.
 11/12 + 12/13 + 14/15 gives Eb/N0 = -3.0 dB.
 11/12 + 12/13 + 14/15 + 15/16 gives Eb/N0 = -2.5 dB.
 11/12 + 12/13 + 14/15 + 17/18 gives Eb/N0 = -3.4 dB.

There's some phase changing going on here which is making
stacking not so effective.

--
Paul Nicholson
--