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Re: LF: T/A OPDS

To: <[email protected]>
Subject: Re: LF: T/A OPDS
From: "Markus Vester" <[email protected]>
Date: Sat, 19 Oct 2013 21:36:15 +0200
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Stefan, LF,
 
very nice! Thanks for the link to the UA0SNV monitor.
 
Yes if there is fading during the sequence this will widen the carrier, just like any other amplitude or phase modulation. For medium distances with multiple skywave modes, fading periods on LF could be on the order of 10 to 20 minutes, equivalent to a millihertz or two. Longer paths tend to be more stable with slower fading because the steep skywave components have died out.
 
But keep in mind that a wider peak might also have been caused by a small receiver drift.
 
BTW In my other posting I hadn't explained the last dB number in the opds result line. This describes the quality of the match to the callsign template, ie how many dBs the highest peak in the cross-correlation function exceeds its average power, which comes from noise and autocorrelation sidelobes. The range is from about 22 dB for a perfect signal, down to a chosen threshold of 15 dB where false positives start to appear occasionally.
 
I also intend to send more Op-32 later tonight.
 
All the best,
 
Markus (DF6NM)
 
 

Sent: Saturday, October 19, 2013 9:11 PM
Subject: Re: LF: T/A OPDS

Markus and OPDS fans,

On the page of UA0SNV, http://dl.dropboxusercontent.com/u/76751319/opds32.txt i just found this text:

UA0SNV OO18JB Opera-32 correlation     http://df6nm.bplaced.net/opera/opds.zip

   date      time   call   distance  frequency bandwidth  snr    correlation

2013-10-19 19:00:33 DK7FC   5745km 137560.111Hz   5mHz -49.1dBOp  81% 15.7dB
2013-10-19 18:20:32 DK7FC   5745km 137560.110Hz   5mHz -44.1dBOp 100% 19.1dB

So it also works over the land path of that distance.

It appears to me that, if the transmitted coherent signal and the receiver is stable, the x-mHz reading says something about the phase stability of the path (?).

Markus, good luck! In an hour or so i willy QSY to 472 kHz CW but will be back at night.

73, Stefan/DK7FC
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