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Date: Sat, 19 Oct 2013 00:38:56 +0200
From: =?ISO-8859-1?Q?Stefan_Sch=E4fer?= <Stefan.Schaefer@iup.uni-heidelberg.de>
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Subject: Re: LF: T/A OPDS DK7FC
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Markus,

Wow, somehow genial! Where did you learn to make such a program? Thanks=20
for the explanations.

What is the next challenge? WSPRDS?? Isn't it possible to correlate WSPR=20
signals as well?

73, Stefan, on air now!

Am 18.10.2013 17:41, schrieb Markus Vester:
> Stefan, Jay, John,
> the "96%" number shows the temporal overlap between the receive period=20
> (ie the duration of the currently used FFT, about 35 minutes) and=20
> the identified Op sequence (33 minutes). With 10 minutes spacing=20
> between subsequent FFTs, the sequence does not always fit completely=20
> into one of the slots. so it says that 96% of the sequence was=20
> included in the evaluation. However the missing part has only=20
> neglegible impact on the detection sensitivity.
> Ideally Opera can be treated as an AM signal, with a central carrier=20
> and modulation sidebands around it. The "2mHz" bandwidth figure refers=20
> to the bandwidth of the carrier, which should be as small as possible.=20
> Opds applies some smoothing to the power spectrum and then tries to=20
> measure the -10 dB bandwidth of the central peak. Stable and phase=20
> coherent signals consistently show less than 3 mHz bandwidth. An=20
> intermediate width up to about 30 mHz typically indicates a coherent=20
> signal but with a slight thermal drift. Even higher bandwidth (~ 100=20
> mHz) are mostly due to incoherent keying, ie random phase dashes=20
> caused by stopping the TX oscillator or divider during gaps.
> Opds internally uses an "autofocus" concept similar to synchroneous=20
> demodulation, where the central spectral peak is used as a phase=20
> reference. Narrower carriers produce better demodulated SNR. For=20
> fading or incoherent signals, the phase has to be tracked faster or=20
> even on a dash-by-dash basis, which is much less efficient.
> The "dBOp" column is showing SNR according to Jos=E9's Opera scale,=20
> which is approximately based on average power. It shows 4 dB more=20
> negative values than the standard WSPR scale, ie. carrier power in 2.5=20
> kHz. A marginally decode with WSPR-15 would need -38 dB, and an Opera=20
> signal with same PEP would then show as -42 dBOp. For a coherent=20
> signal, the Opds-32 threshold should be around -50 dBOp, which in=20
> theory is 8 dB better than WSPR-15 and 11 dB better than standard=20
> Opera-32.
> Please be aware that the SNR figures shown in opds results can=20
> sometimes be inaccurate. With an incoherent signal, often not all of=20
> the carrier power is captured during the bandwidth measurement,=20
> producing a low or invalid SNR reading. The SNR measurement also=20
> doesn't work well for strong signals (> -20 dBOp), eg for DK7FC who=20
> should really be plus several dB here.
> So why was Stefan's TA signal not stronger last night? My guess is=20
> that TA propagation just didn't extend into central Europe: While UK=20
> and duch stations received Bob well on 74 kHz, little or nothing at=20
> all apperared on Hartmut's and my 74 kHz grabbers.
> Best 73,
> Markus (DF6NM)
> PS The weather has improved here, so I have put out the TX antenna for=20
> a possible joint TA session tonight.
>
> *From:* Stefan Sch=E4fer <mailto:Stefan.Schaefer@iup.uni-heidelberg.de>
> *Sent:* Friday, October 18, 2013 2:36 PM
> *To:* rsgb_lf_group@blacksheep.org <mailto:rsgb_lf_group@blacksheep.org=
>
> *Subject:* Re: LF: T/A OPDS DK7FC
>
> Hi John, Jay, Markus,
>
> OK. Well, it seems to work. But i can't value the results. Why is it=20
> only 96% and what is the meaning of 2 mHz here?
> Seems the S/N is rather low. Condx must have been poor.
> Were there other reports from US stns?
>
> 73, Stefan/DK7FC
>
> Am 18.10.2013 13:05, schrieb John Andrews:
> Stefan, Markus, Jay,
>
> Results from last night:
>
> 2013-10-18 05:09:25 DK7FC   5981km 137560.016Hz   2mHz -42.8dBOp  96%=20
> 20.6dB
> 2013-10-18 04:29:25 DK7FC   5981km 137560.016Hz   2mHz -44.8dBOp =20
> 96% 17.8dB
> 2013-10-18 03:49:23 DK7FC   5981km 137560.016Hz   2mHz -44.0dBOp =20
> 96% 20.3dB
> 2013-10-18 03:09:23 DK7FC   5981km 137560.017Hz   2mHz -43.7dBOp =20
> 96% 19.0dB
> 2013-10-18 02:29:23 DK7FC   5981km 137560.016Hz   3mHz -47.5dBOp =20
> 96% 17.9dB
> 2013-10-18 01:49:23 DK7FC   5981km 137560.016Hz   3mHz -46.4dBOp =20
> 80% 16.8dB
> John, W1TAG
>

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Markus, <br>
<br>
Wow, somehow genial! Where did you learn to make such a program? Thanks
for the explanations.<br>
<br>
What is the next challenge? WSPRDS?? Isn't it possible to correlate
WSPR signals as well?<br>
<br>
73, Stefan, on air now!<br>
<br>
Am 18.10.2013 17:41, schrieb Markus Vester:
<blockquote cite="mid:C6FD126FE3284F95A6ED7213B3C0618B@White"
 type="cite">
  <meta http-equiv="Content-Type"
 content="text/html; charset=ISO-8859-1">
  <meta content="MSHTML 6.00.6000.21352" name="GENERATOR">
  <div><font face="Arial" size="2">Stefan, Jay, John,</font></div>
  <div>&nbsp;</div>
  <div><font face="Arial" size="2">the "96%" number shows the temporal
overlap between the receive period (ie the duration of the&nbsp;currently
used&nbsp;FFT, about 35 minutes) and the&nbsp;identified Op sequence (33
minutes). With&nbsp;10 minutes spacing between subsequent FFTs, the sequence
does not always fit completely into one of the&nbsp;slots. so it says that
96% of the sequence was included in the evaluation. However the missing
part&nbsp;has only neglegible impact on the detection sensitivity.</font></div>
  <div>&nbsp;</div>
  <div><font face="Arial" size="2">Ideally Opera&nbsp;can be treated&nbsp;as an
AM signal, with a central carrier and modulation sidebands around it.
The "2mHz" bandwidth figure refers to the bandwidth of the carrier,
which should be as small as possible. Opds applies some smoothing to
the power spectrum and then tries to measure the -10 dB bandwidth of
the central peak. Stable&nbsp;and phase coherent signals consistently show
less than 3 mHz bandwidth. An intermediate width&nbsp;up to about 30
mHz&nbsp;typically indicates a coherent signal&nbsp;but with a slight thermal
drift. Even higher bandwidth (~ 100 mHz) are mostly&nbsp;due to&nbsp;incoherent
keying, ie random phase dashes caused by stopping the TX oscillator or
divider during gaps. </font></div>
  <div>&nbsp;</div>
  <div><font face="Arial" size="2">Opds internally uses an "autofocus"
concept similar to synchroneous demodulation, where the central
spectral peak is used as a phase reference.&nbsp;Narrower
carriers&nbsp;produce&nbsp;better demodulated SNR. For fading or incoherent
signals, the phase has to be tracked faster or even on a dash-by-dash
basis, which is much less efficient.</font></div>
  <div>&nbsp;</div>
  <div><font face="Arial" size="2">The "dBOp" column is showing SNR
according to Jos&eacute;'s Opera scale, which is approximately based on
average power. It shows 4 dB more negative values than the standard
WSPR scale, ie. carrier power in 2.5 kHz. A marginally decode with
WSPR-15 would need -38 dB, and&nbsp;an Opera signal with same PEP would then
show as -42 dBOp. For a coherent signal, the Opds-32 threshold should
be&nbsp;around -50 dBOp, which in theory is 8 dB better than WSPR-15 and 11
dB better than standard Opera-32.</font></div>
  <div>&nbsp;</div>
  <div><font face="Arial" size="2">Please be aware that the SNR figures
shown in opds results&nbsp;can sometimes be inaccurate. With an incoherent
signal,&nbsp;often not all of the carrier power is captured during the
bandwidth measurement, producing&nbsp;a low or invalid SNR reading.&nbsp;The&nbsp;SNR
measurement also doesn't work well for strong signals (&gt; -20 dBOp),
eg for DK7FC who should really be plus several dB here.</font></div>
  <div>&nbsp;</div>
  <div><font face="Arial" size="2">So why was Stefan's TA signal not
stronger last night? My guess is that&nbsp;TA propagation just didn't
extend&nbsp;into central Europe: While UK and duch stations received Bob
well on 74 kHz, little or nothing at all apperared&nbsp;on Hartmut's and my
74 kHz grabbers.</font></div>
  <div>&nbsp;</div>
  <div><font face="Arial" size="2">Best 73,</font></div>
  <div><font face="Arial" size="2">Markus (DF6NM)</font></div>
  <div>&nbsp;</div>
  <div
 style="font-family: Tahoma; font-style: normal; font-variant: normal; font-weight: normal; font-size: 10pt; line-height: normal; font-size-adjust: none; font-stretch: normal; -x-system-font: none;">
  <div>
  <div><font face="Arial" size="2">PS The weather&nbsp;has&nbsp;improved here,
so&nbsp;I have put out the TX antenna for a possible joint TA session
tonight.</font></div>
  <div>&nbsp;</div>
  <br>
  </div>
  <div
 style="background: rgb(245, 245, 245) none repeat scroll 0% 0%; -moz-background-clip: border; -moz-background-origin: padding; -moz-background-inline-policy: continuous;">
  <div style=""><b>From:</b> <a moz-do-not-send="true"
 title="Stefan.Schaefer@iup.uni-heidelberg.de"
 href="mailto:Stefan.Schaefer@iup.uni-heidelberg.de">Stefan Sch&auml;fer</a>
  </div>
  <div><b>Sent:</b> Friday, October 18, 2013 2:36 PM</div>
  <div><b>To:</b> <a moz-do-not-send="true"
 title="rsgb_lf_group@blacksheep.org"
 href="mailto:rsgb_lf_group@blacksheep.org">rsgb_lf_group@blacksheep.org</a>
  </div>
  <div><b>Subject:</b> Re: LF: T/A OPDS DK7FC</div>
  </div>
  </div>
  <div><br>
  </div>
  <div>Hi John, Jay, Markus,<br>
  <br>
OK. Well, it seems to work. But i can't value the results. Why is it
only 96% and what is the meaning of 2 mHz here?<br>
Seems the S/N is rather low. Condx must have been poor.<br>
Were there other reports from US stns?<br>
  <br>
73, Stefan/DK7FC<br>
  <br>
Am 18.10.2013 13:05, schrieb John Andrews:<br>
Stefan, Markus, Jay,<br>
  <br>
Results from last night:<br>
  <br>
2013-10-18 05:09:25 DK7FC&nbsp;&nbsp; 5981km 137560.016Hz&nbsp;&nbsp; 2mHz -42.8dBOp&nbsp; 96%
20.6dB<br>
2013-10-18 04:29:25 DK7FC&nbsp;&nbsp; 5981km 137560.016Hz&nbsp;&nbsp; 2mHz -44.8dBOp&nbsp;
96%&nbsp;17.8dB<br>
2013-10-18 03:49:23 DK7FC&nbsp;&nbsp; 5981km 137560.016Hz&nbsp;&nbsp; 2mHz -44.0dBOp&nbsp;
96%&nbsp;20.3dB<br>
2013-10-18 03:09:23 DK7FC&nbsp;&nbsp; 5981km 137560.017Hz&nbsp;&nbsp; 2mHz -43.7dBOp&nbsp;
96%&nbsp;19.0dB<br>
2013-10-18 02:29:23 DK7FC&nbsp;&nbsp; 5981km 137560.016Hz&nbsp;&nbsp; 3mHz -47.5dBOp&nbsp;
96%&nbsp;17.9dB<br>
2013-10-18 01:49:23 DK7FC&nbsp;&nbsp; 5981km 137560.016Hz&nbsp;&nbsp; 3mHz -46.4dBOp&nbsp;
80%&nbsp;16.8dB<br>
  </div>
  <div>John, W1TAG<br>
  <br>
  </div>
</blockquote>
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