Re: VLF: EbNaut transmissions on lower frequencies?, pre-tests: 6.47kHz

[Markus Vester <markusvester@aol.com>]

Well the manager of the local railway switchyard is a good friend of mine. I could talk him into suspending all freight operations, and diverting a few passenger trains around Nuremberg, enabling him to completely switch off the railway grid  for 24 hours. This resulted in a very significant QRM reduction (more than 20 dB), allowing an easy decode on 6.47 kHz.

No? Ok, I admit I cheated, by reconstructing a wav file from Stefan's "600" grabber images. But what I thought would be a quick few minutes of scripting turned out to be a lengthy exercise. I had everything ready by yesterday afternoon, hoping to surprise everyone with an early decode after half of the message was through. But nothing, not even a false. I spent a couple of hours, optimizing, checking and rechecking the code. In the end I was sure I had every bit right but still no decode, so I gave up.

Looking on Stefan's grabber again this morning, I noticed that the message had ended a couple of hours earlier than calculated, and immediately got the 18 character decode. 

All the best,
Markus



-----Ursprüngliche Mitteilung-----
Von: DK7FC <selberdenken@posteo.de>
An: rsgb_lf_group <rsgb_lf_group@blacksheep.org>
Verschickt: Mi, 18 Mai 2016 10:15 am
Betreff: Re: VLF: EbNaut transmissions on lower frequencies?, pre-tests: 6.47kHz

Hello Markus, Paul, VLF,

Oh, what a surprise! You've got the message with such a high SNR? It is amazing. Congrats to your first decode on 6.47 kHz!
What happened to your QRM? I the Bahn striking again?

Strange, i saw that the message was finished earlier than expected. Actually it should be 20 characters. The message should be 'STEFAN&PAUL@6.47KHZ!' but the '&' and '!' was ignored.
The EbNaut-TX program confirmed 20 characters after writing them in the text field though.

The message was placed into a night-day-night period and QRN was moderate. Paul said that night propagation is better than day propagation and maybe the QRN of the night is rather in the 'foreground' so it can be blanked more effective.
BTW the antenna current was even 250 mA and quite constant!
Yesterday i considered to solder on the PA and add new components while it was transmitting ;-) But then i convinced myselfe to continue on other projects ;-) But today is the day..

Now i hope for Paul to get some good results.

73 and thanks for trying to receive/decode.
Stefan

Am 18.05.2016 09:05, schrieb Markus Vester:

Hi Stefan, Paul,

that message was only 18 characters long! Decode attached.

73, Markus

-----Ursprüngliche Mitteilung-----
Von: DK7FC <selberdenken@posteo.de>
An: rsgb_lf_group <rsgb_lf_group@blacksheep.org>
Verschickt: Mo, 16 Mai 2016 10:53 pm
Betreff: Re: VLF: EbNaut transmissions on lower frequencies?, pre-tests: 6.47kHz

Hi Paul, VLF,

A spontaneous impulse/idea:

Let's be optimistic and try the long message in 100s symbols. The announcement happens a few minutes before the start of the transmission :-)

f = 6470.00000 Hz
Start time: 16.05.2016   21:00:02 UTC
Symbol length: 100 s
Characters: 20
CRC 16
Coding 8K19A
Duration: 34h, 13m, 20s
Antenna current: 240 mA

16K25A and 200s, that's a job for the lower frequencies. I have to send the mail now, otherwise it comes to late ;-)

73, Stefan

Am 16.05.2016 07:38, schrieb Paul Nicholson:

Stefan wrote:

> would you think that going from 100s to 200s will improve
> things by about 3 dB?

Yes, or better: keeping to 100s and going to a 16K mode instead
of 8K for an increase of coding gain.

> How long do you record the VLF soundcard stream?

About 65 months at the moment.

> Would it be possible, for example, to transmit a 1 week long
> message, without an announcement before the start?

Yes, in principle.  The longer the message the more chance of
a battery problem or sheep knocking down one of the antennas,
or thunderstorm or power cut, or one of the cats sleeping on
top of the GPS antenna.

But with a long message, an interruption of a few hours is
not a disaster.  After a power cut, my rx will restart with
the same reference phase and continue recording so there will
be a gap but no loss of phase.

We may have to put this to use when we reach ULF.

Un-announced is ok because of the continuous recording but better
to announce if possible so that I know not to do maintenance
(or tests with kites! Will be playing with the Power Sled 24).

--
Paul Nicholson
--