Date: Thu, 12 Nov 2015 17:44:33 -0330 (NST)
From: jcraig@mun.ca
To: rsgb_lf_group@blacksheep.org
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 <8D2EB5632CCBBF3-2188-4C745@webmail-vd012.sysops.aol.com>
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Subject: Re: LF: VO1NA frequency
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Hi Markus,

Convinced that the oscillator had drifted since calibration 2 years ago,
I tweaked the DOXCO up 0.05 Hz and was happy to see the result on your=20
OPDS page.

Thanks for the tips on getting started on EbNaut.  I'll tinker with it
and hopefully make some progress. Our cat seems anxious lately!

73
Joe

On Thu, 12 Nov 2015, Markus Vester wrote:

> Hi Joe,
> =C2=A0
> an interesting change happened last night: as far as I can see, your freq=
uency has shifted to nominal 137477.000 at 22:45 UT, and appeared to be rat=
her stable thereafter.
> =C2=A0
> Regarding EbNaut transmit: I haven't tried it on our RasPi yet. Both Dome=
nico and I have run the Windows version of ebnaut-tx, in conjunction with U=
SB-to-serial converters. RS-232 lines are normally current-limited to 20 mA=
 so they can be directly connected to the DC-coupled IF input of any ring m=
ixer. On 137 kHz, I used a Minicircuits ZAY3. As I have a linear PA I inser=
ted a simple 500uF/100ohm shaping filter to reduce=C2=A0keying sidebands, b=
ut this may not be essential. This mixer won't work on VLF 8.3 kHz so I use=
d an old telephone relay there, but due to contact bouncing the transitions=
 were less than perfect. Domenico uses an SSB exciter on LF, and he made a =
dedicated diode mixer with audio transformers to apply PSK on 1502 Hz.
> =C2=A0
> Our current receiving method re-uses opds32 data files and is thus limite=
d to sequence durations of a bit over half an hour. For example, using EbNa=
ut 8K19A encoding with 1 second symbols would fit 31 characters into 29.3 m=
inutes, and the message could be repeated half-hourly. Yesterday your opds =
carrier was weakly visible until midday in Europe, so daytime TA decodes mi=
ght be possible using slower rates (e.g. 5 seconds).
> =C2=A0
> Our cat seems to be very curious about radio, so I thought he might feel =
a desire to communicate with his fellows overseas. Rumour has it that at le=
ast in one instance, Uwe's cat=C2=A0successfully managed to take control of=
 the DJ8WX VLF transmitter ;-)
> =C2=A0
> All the best,
> Markus (DF6NM)
>
>
>
>
> -----Urspr=C3=BCngliche Mitteilung-----
> Von: Markus Vester &lt;markusvester@aol.com&gt;
> An: rsgb_lf_group &lt;rsgb_lf_group@blacksheep.org&gt;
> Verschickt: Mi, 11 Nov 2015 6:12 pm
> Betreff: Re: LF: VO1NA frequency
>
>   Joe,
>  =C2=A0
>  more of the same from last night, this time with=C2=A0frequency and leve=
l plots. Again we see some frequency variation of similar size as yesterday=
=2E It is not clear how much of that is due to propagation,=C2=A0I only thi=
nk that the=C2=A0rise=C2=A0near the end is due to Doppler=C2=A0from the=C2=
=A0descent of the ionosphere at sunrise.=C2=A0Russian=C2=A0Loran lines on 1=
37475 and 137482.5 seemed to have less overnight variation (~ 0.1 mHz), but=
 then of course the intra-European path from Slonim is very different from =
yours.=C2=A0
>  =C2=A0
>  Regarding EbNaut carrier analysis:=C2=A0for some reason (lack of coffee?=
), I only saw Domenico's earlier mail after I had=C2=A0sent mine, so please=
 excuse me for basically having described=C2=A0the same procedure again.=C2=
=A0Anyway it's good that we=C2=A0both=C2=A0arrived at the same conclusion:=
=C2=A0If Joe started sending=C2=A0EbNaut PSK with his=C2=A0oscillator as=C2=
=A0it is now, we would very likely be able to decode it here.=C2=A0
>  =C2=A0
>  Joe so all you need now is a diode ring-mixer for PSK modulation and Pau=
l's ebnaut-tx program.=C2=A0Symbol=C2=A0timing=C2=A0will=C2=A0be derived fr=
om=C2=A0the PC clock,=C2=A0so with NTP=C2=A0available there's no need to in=
volve GPS at all. If Paul brought his LF receiver back to life, he could pr=
obably copy you even=C2=A0if you reduced=C2=A0TX power to 0.1 Deccas.
>  =C2=A0
>  How many cats do you have? We want to know=C2=A0names, colours, sex and =
age for all of them ;-)
>  =C2=A0
>  All the best,
>  Markus (DF6NM)
>  =C2=A0
>  =C2=A0
>  PS. SpecLab question: Wolf is there a way to extract peak frequencies fr=
om past spectrogram lines (semi-)automatically, without having to manually=
=C2=A0move=C2=A0and read the mouse cursor over each point, e.g. something l=
ike a peak_f(f1,f2, time) interpreter function?
>
>  =C2=A0
> -----Urspr=C3=BCngliche Mitteilung-----
> Von: Markus Vester &lt;markusvester@aol.com&gt;
> An: rsgb_lf_group &lt;rsgb_lf_group@blacksheep.org&gt;
> Verschickt: Mi, 11 Nov 2015 1:24 am
> Betreff: LF: VO1NA frequency
> =C2=A0         Hi Joe,
>   =C2=A0
>   the attached plot shows the  frequency=C2=A0stability of=C2=A0your=C2=
=A0opds trace received last  night=C2=A0http://df6nm.bplaced.net/LF/opds32_=
151110_0736.png=C2=A0.  Each data point is the interpolated peak of a  sing=
le 438 uHz FFT (i.e. 38 minute window). The average frequency seems to be  =
0.7 mHz below=C2=A0nominal, and there are small temporal variations=C2=A0up=
  to=C2=A00.5 mHz in either direction.=C2=A0Though some of that=C2=A0is  pr=
obably=C2=A0attributable=C2=A0to noise and propagation, I believe that ther=
e  is also a bit of inherent instability in=C2=A0the frequency  source.=C2=
=A0Actually a few parts per billion=C2=A0is quite good for a free  running=
=C2=A0OCXO (assuming the "D" stands for  "double oven" and not "discipled")=
, and that the calibration was done over a 10  MHz=C2=A0HF link.
>   =C2=A0
>   Is this good enough for EbNaut? During the  experiments with IZ7SLZ we =
found that for full sensitivity the phase variation  over the EbNaut=C2=A0s=
equence duration should not be much more than 90=C2=B0. Thus  for a half-ho=
ur message the frequency should be ideally constant and known to  about 0.1=
4 mHz. If there is more variation=C2=A0we=C2=A0often=C2=A0can still  get=C2=
=A0decodes, but we will have to find the best frequency offset by trial  an=
d error, which can be cumbersome if the signal is weak.
>   =C2=A0
>   I also fed opds data files from your Sat/Sun  transmissions to the EbNa=
ut=C2=A0decoder. The idea was to see if=C2=A0your Opera  transmissions woul=
d actually produce=C2=A0the all-asterisk=C2=A0decode which is  expected for=
 a non-PSK-keyed straight carrier, and to observe the symbol phase  evoluti=
on over the 38 minute duration.=C2=A0Starting midnight UT, one decode was a=
ttempted every 30 minutes,  using a setting for 464 raw symbols (4 characte=
rs)=C2=A0and 5 seconds per  symbol. A=C2=A0frequency offset of -0.6 mHz was=
=C2=A0selected=C2=A0to obtain  flat phase during the first decodes, and=C2=
=A0that offset=C2=A0was=C2=A0kept for  all later attempts. Despite the Oper=
a gaps  which=C2=A0degrade or drop half of the available symbols,=C2=A012 o=
ut of 13  decode attempts=C2=A0produced the  correct=C2=A0"****" message,=
=C2=A0e.g. http://df6nm.bplaced.net/LF/r0317.png  . However at times the fr=
equency drift was quite visible=C2=A0on the=C2=A0phase  plot,=C2=A0e.g. in =
http://df6nm.bplaced.net/LF/s0317.png=C2=A0(flat  phase around 3:17) versus=
 http://df6nm.bplaced.net/LF/s0347.png=C2=A0(upward  phase slope around 3:4=
7).=C2=A0
>   =C2=A0
>   Scaling down to VLF, deviations from the same  oscillator will be 16x s=
maller (~30 uHz at 8.3 kHz). This will be probably good  enough even for=C2=
=A0narrow FFT bins, corresponding to several hours coherent  carrier integr=
ation or slow EbNaut decodes.
>   =C2=A0
>   All the best,
>   Markus (DF6NM)
>
>
>     From: jcraig@mun.ca
>   Sent: Saturday, November 07, 2015 3:45 PM
>   To: rsgb_lf_group@blacksheep.org
>   Subject: Re: LF: VO1NA opds-32
>
>
>
>
> LF Group,
>
> Again, thanks to SV8RV DF2JP PA7EY and DF6NM for  the reports.
>
> In my last post I reported the drift was constrained to  within 1 Hz.
> This should be 1 mHz.=C2=A0 Thanks Markus for your assurances  that this
> should be adequate for EbNaut which I hope to use to send send our
> cat's name on LF.=C2=A0 The little curls appear often on the QRSS traces =
 on
> your high res spectra.=C2=A0 Doppler variations were removed from the 10 =
 MHz
> WWV signals with harmonic regression when the DOCXO was calibrated
> so  this effect is seen on LF but not as strongly.
>
> After=C2=A0 reading about  EbNaut on Paul Nicholson's pages it seems I ha=
ve
> much catching up  ahead.=C2=A0 Fasinating stuff!
>
> Can the EbNaut phase inversions be done  without an absolute time
> reference?=C2=A0 I'm cheap and lazy so hoping GPS  will not be needed.
>
> The Opera will be doing an encore tonight and if the  wind stays low
> a tower climbing expedition is planned for the  afternoon.
>
> 73
> Joe VO1NA
> ...
>
>
>
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