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Edgar J Twining from Tasmania asked the same a while ago. = You'll find the respective emails posted beneath.=20 Best 73, Markus (DF6NM) From: Graham=20 Sent: Saturday, June 22, 2013 9:48 PM To: rsgb_lf_group@blacksheep.org=20 Subject: Re: LF: VO1NA Opera-32 Marcus=20 Q what advantage could you have , using this to detect wspr-15 ? th= at has a fixed pattern and a known start time ?=20 G.. From: Markus Vester=20 Sent: Thursday, February 21, 2013 1:10 AM To: edgar=20 Subject: Re: "Deep search analysis" Edgar, yes, at least in principle. I had actually looked into WSPR and QRSS correl= ation before turning to Opera. With Opera, it looks like I can detect up to= 10 to 12 dB deeper than the standard decoder. But I think there is simply = less to gain with WSPR. The first step in my procedure is searching for a carrier. If Opera is tran= smitted phase-coherently, it's just classic AM, with 50 % of the transmitte= d energy contained in a central spectral line. This is relatively easy to d= etect eg. with a long 0.47 mHz FFT. On the other hand, WSPR shares it's "ca= rrier" power among four equispaced lines, which lets them stand out less ab= ove the noise.=20 My second step then uses the detected carrier as a pilot to correct for sma= ll amounts of drift and propagational phase variations. This could probably= be done equally well with a coherent sum of four carriers as long as their= spacing is accurate. The third step, the actual correlation against a numb= er of precalculated list of templates, should also be comparable for the tw= o modes. The main difference is however that Joe's WSPR decoder seems to be much mor= e efficient in the first place than Jose's bit-power based Opera decoder. F= or same message time, the difference is said to be about 6 to 7 dB. So ther= e is simply less to gain by using all the available signal energy in a corr= elation process. Another difficulty is that WSPR actually transmits more information than ju= st the callsign. So for preparing the templates, you would have to include = locator and power as a priori information. I have also looked at integrating subsequent repeats of WSPR. It is fairly = straightforward to stack them incoherently, in essence like averaging the b= rightness of successive spectrograms. However this gains only 1.5 dB per do= ubling of aquisition time. Coherent superposition is more attractive (3 dB = for double time), but requires extremely stable signals over long periods o= f time, and a milliHz search for the exact phase shift from one repeat to t= he next. Best 73, Markus (DF6NM) ----- Original Message -----=20 From: edgar=20 To: Markus Vester=20 Cc: Stefan Sch=E4fer=20 Sent: Wednesday, February 20, 2013 12:49 AM Subject: "Deep search analysis" Hi Markus, Can you "deep search analysis" that you applied to OPERA signals be use= fully applied to WSPR signals? Regards, Edgar. =20 ------=_NextPart_000_0010_01CE6F97.3E296C50 Content-Type: text/html; charset=ISO-8859-1 Content-Transfer-Encoding: quoted-printable  
=20=20=20=20=20=20 =20=20=20=20=20=20

Hi Graham,
 
good question... Edgar J Twining = from Tasmania=20 asked the same a while ago. You'll find the respective emails pos= ted=20 beneath. 
 
Best 73,
Markus (DF6NM)

From:=20 Graham
Sent: Saturday, June 22, = 2013 9:48=20 PM
Subject: Re: LF: VO1NA=20 Opera-32
<= FONT size=3D"2">
Marcus
 
Q   what  advantage cou= ld you =20 have , using  this to  detect  wspr-15  ? that  ha= s=20 a  fixed  pattern  and a  known start time ?
 
G..
<= FONT size=3D"2">
From: <= /FONT>Markus Vester
Sent: Thursday, Febr= uary 21,=20 2013 1:10 AM
To: edgar
Subject: Re: "Deep search analysis"
=
= Edgar,
=  
= yes, at=20 least in principle. I had actually looked into WSPR and QRSS correlation be= fore=20 turning to Opera. With Opera, it looks like I can detect up to 10 to 1= 2 dB=20 deeper than the standard decoder. But I think there is simply less to = gain=20 with WSPR.
=  
= The first=20 step in my procedure is searching for a carrier. If Opera is transmitt= ed=20 phase-coherently, it's just classic AM, with 50 % of=20 the transmitted energy contained in a central spectral line.=20 This is relatively easy to detect eg. with a long 0.47 mHz FFT. O= n the=20 other hand, WSPR shares it's "carrier" power among four= =20 equispaced lines, which lets them stand out less above the noise.=20
=  
= My second=20 step then uses the detected carrier as a pilot to correct for small amounts= of=20 drift and propagational phase variations. This could probably be done=20 equally well with a coherent sum of four carriers as long as their spa= cing=20 is accurate. The third step, the actual correlation against a number of=20 precalculated list of templates, should also be comparable for the two=20 modes.
=  
= The main=20 difference is however that Joe's WSPR decoder seems to be much mo= re=20 efficient in the first place than Jose's bit-power based Opera decoder. For= same=20 message time, the difference is said to be about 6 to 7 dB. So there is sim= ply=20 less to gain by using all the available signal energy in a correlation= =20 process.
=  
= Another=20 difficulty is that WSPR actually transmits more information than just the=20 callsign. So for preparing the templates, you would have to include lo= cator=20 and power as a priori information.
=  
= I have also=20 looked at integrating subsequent repeats of WSPR. It is fairly=20 straightforward to stack them incoherently, in essence like averaging the=20 brightness of successive spectrograms. However this gains only 1.5 dB = per=20 doubling of aquisition time. Coherent superposition is more attractive= (3=20 dB for double time), but requires extremely stable signals over long=20 periods of time, and a milliHz search for the exact phase shift from one re= peat=20 to the next.
=  
= Best=20 73,
= Markus=20 (DF6NM)
=  
----- Original Message= -----=20
From: edgar=20
Sent: Wednesday= ,=20 February 20, 2013 12:49 AM
Subject: "Deep = search=20 analysis"
=
= Hi=20 Markus,
=  
=     Can you "deep search analysis" that you applied to=20 OPERA signals be usefully applied to WSPR signals?

Regards,=20 Edgar.
=
 

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