Date: Mon, 12 Dec 2016 08:54:08 -0330 (NST)
From: jcraig@mun.ca
To: rsgb_lf_group@blacksheep.org
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Message-ID: <Pine.LNX.4.64.1612120846120.24211@plato.ucs.mun.ca>
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Subject: Re: LF: VO1NA received my EbNaut
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Hi Markus, Group,

Congrats again on this work.  I was very satisfying to be part of it.
I'll follow though on your advice. The SR is now calibrated at 12k.=20
Another option is raspi. It is already set to ntp and it does not=20
use a silly operating system.

At the moment I must QSY to the uni to pick up a friend.  We are going to=
=20
Signal Hill to fly a kite in honour of Marconi!

73
Joe

On Mon, 12 Dec 2016, Markus Vester wrote:

> Hi Joe, LF,
>
>
> after obtaining that first decode, I was able to improve the result signi=
ficantly by tweaking time and frequency offsets. However during this optimi=
zation, the little blue peak in the spectrum-of-squares which had initially=
 guided me disappeared completely. So this peak must have been just a lucky=
 coincidence. Starting from these parameters, I could then get decodes from=
 the 4 and 5 UT transmissions as well:
>
>
> file          df       dt       EbN0
> hhmm    Hz       s      sym  carr
>
>
> 0408  -9.8832  556.1  2.6  -0.6
> 0508  -9.8832  556.0 -0.7  -3.5
> 0608  -9.8831  555.9  5.4   0.5
>
>
> So we know now that the PC clock was around 3.4 s late at the time, and y=
our DDS pilot is 0.8 mHz below 137.5 kHz (albeit this assumes 12000.0 Hz sa=
mplerate which may not be correct).
>
>
> Let me suggest the next steps on the receiver side:
>
>
> 1. Align the PC clock to UT within say 0.2 s. There are several options f=
or NTP: Here I am using a small utility called SNTP which G3PLX gave me som=
e years ago, which avoids clock jumps by gradually adjusting clock speed. W=
olf's rsNTP also worked fine for me, and is able to include a deliberate of=
fset to compensate for long sound path latency. I haven't tried Dimension-4=
 software but it has been employed successfully by a number of LF amateurs.=
 Last not least IZ7SLZ made his own clock-setting utility using serial NMEA=
 from a GPS.
>
>
> 2. Use the calibrated 12 kHz samplerate for decoding. This will minimize =
residual symbol-timing errors, and allow us to accurately predict the frequ=
ency offset for other transmit frequencies.
>
>
> 3. Let SpecLab's frequency offset detector track the pilot. This will mak=
e the decoding process more comfortable, because we won't need to measure t=
he RX frequency offset individually for each run.
>
>
> All the best, and thanks again
>
>
> 73, Markus (DF6NM)
>
>
>
> -----Urspr=C3=BCngliche Mitteilung-----
> Von: Markus Vester <markusvester@aol.com>
> An: rsgb_lf_group <rsgb_lf_group@blacksheep.org>
> Verschickt: So, 11 Dez 2016 11:21 pm
> Betreff: LF: VO1NA received my EbNaut
>
>
>
>
>
>
> Hi Joe,
>
>
> we made it! But only with a lot of luck.
>
>
> Using default frequency and samplerate parameters, I first looked for the=
 DDS pilot in your nine files and noted the frequency offsets:
>
>
> file      pilot
> hhmm    Hz
>
> 2208  .1157 (pilot turned on half-way)
> 2308  .1148
> 0008  .1147
> 0108  .1149
> 0208  .1156
> 0308  .1160
> 0408  .1162
> 0508  .1161
> 0608  .1161
>
>
> Thus I concluded that your rx might have small enough drift over 22 minut=
es. Then I took the file for my last transmission (12110608.txt) and calcul=
ated nominal frequency and start time offsets:
>
> freq: +0.1161 - 10.000 =3D -9.9839 Hz,
> time: 6:00:00.3 - 5:50:40.92 =3D 559.38 s.
>
>
> You said that your clock was about 5 seconds slow, so I started searching=
 around 554.4 s offset. The signal is too weak to be seen directly, and I h=
adn't sent any plain carriers before or after which would have helped findi=
ng at least the right frequency. After some playing around I focused on one=
 of the nearby small blue peaks, and tweaked both offsets to center and max=
imize it more, but no decode happened. Then I tried shifting the timing in =
2 second whole-symbol steps. Each time I waited for the decoder to work it'=
s way through all the phase combinations, loosing more and hope with only g=
ibberish decodes. Finally near the end of the third long run, suddenly my m=
essage "HELLO LF" stared back at me: Oh my god, we've really made it!
>
>
> Congratulations, Joe!
>
>
> Let's call it a day now,
> 73, Markus (DF6NM)
>
>
>
> Re: LF: EbNaut tests 137.490 kHz/OFFLINE
> Von: Markus Vester <markusvester@aol.com>
> An: jcraig <jcraig@mun.ca>
> Datum: So, 11 Dez 2016 8:53 pm
>
>
> Hi Joe,
>
>
> thanks for the files! I have successfully downloaded them from your site,=
 and will now start looking for possible signals.
>
>
> Best 73,
> Markus (DF6NM)
>
>
>
> -----Urspr=C3=BCngliche Mitteilung-----
> Von: jcraig <jcraig@mun.ca>
> An: Markus Vester <markusvester@aol.com>
> Verschickt: So, 11 Dez 2016 6:50 pm
> Betreff: Re: LF: EbNaut tests 137.490 kHz/OFFLINE
>
>
> Hi Markus,
> The files are uploaded to http://www.ucs.mun.ca/~jcraig/ebnaut/
> Lets hope my inexperience hasn't messed up this experiment completely!
>
> The screen dump appears to have been made 1317 utc this morning and
> the computer is set to utc but is slow by ~5s. These brief carriers
> are eigmatic -- I don't know what causes them.
>
> The pilot was generated using an ad9851 without the x6 multiplier
> and a 10 MHz clock. It seems the raspi python maths retains
> the full 32 bit precision for the frequency word. A 0.5 was
> added before the ratio was written to an integer from a float to
> minimise the rounding error.
>
> Please let me know if you need anything else. I'll review the
> hints you sent. Thank-you!
>
> 73 & Good Luck!
>
> Joe
> ...
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