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Re: LF: VO1NA - 137.7770 kHz

To: <[email protected]>
Subject: Re: LF: VO1NA - 137.7770 kHz
From: "Graham" <[email protected]>
Date: Fri, 7 Jun 2013 15:46:13 +0100
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Ok Marcus
Thanks for the  info on the  no-go  zones ,  the  decoder is quite  robust  in terms of  carrier  in the  pass   band , i think  64  decodes are  possible  , may be  less  on the  narrow  windows , but still  only  some  5  or 10 hz separation needed 
I was  relating to the  correlation <> Op signal  , where  normally  only the  time  is normally  selected  by the  operator , the  software  looking  for the  lowest s/n to  place the  carrier , a good  idea in tx/rx   but not  for tx only  , especially  if there  is a  30 min wait to  see  if  anything  happens .. but  better  than  testing  the  4  hour  version ..
73 -G.  

Sent: Thursday, June 06, 2013 11:47 PM
Subject: Re: LF: VO1NA - 137.7770 kHz

Hi Graham,
yes it's true that the opds correlation detector does not attempt to directly decode any of the Opera 28-bit message contents (ie. the callsign). But you do get more than a single yes-or-no information. Opds tells you fairly reliably which entry from the predefined callsign list actually produced the hit. The list currently contains 28 candidates which makes up about 5 bits worth. Also it measures the TX carrier frequency down to a milli-Hz out of a 100 Hz range, which in itself could be used to encode another 17 bits... So I'd say it gives you less than 28 bits but certainly more than one bit.
Best wishes,
Markus (DF6NM)

From: Graham
Sent: Thursday, June 06, 2013 7:13 PM
Subject: Re: LF: VO1NA - 137.7770 kHz

Where  as Op is  designed to  use  standard tx/rx  and  soundcards  with
afc  routines , Marcus  is  running  a  correlation  process  , looking  for
the  pattern  match , this  in effect  is  decoding  a single  data  'bit'
and  stability  will  affect his  decode  system , but  with another 10 dB
s/n it  may extend the  range  considerably !

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