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Re: LF: VO1NA Op32 137.555 kHz

To: <[email protected]>
Subject: Re: LF: VO1NA Op32 137.555 kHz
From: "Graham" <[email protected]>
Date: Sun, 30 Jun 2013 00:26:22 +0100
Importance: Normal
In-reply-to: <[email protected]>
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Well  Markus  ,   Those of us with  radio  controlled  clock's   salute  you  !
[And  with  dfc39-1  just  down the  road , it  must be  a  hostile  radio  environment  ...]
To  extract the  s/n / dB levels  from  Op , getting the  recovered  signal to the  dsp engine  with as  little  change to the  parameters as possible  is  critical . as the  system is  self  sync'  , the  main  concern is the   % noise to  tx  time , in 32  mins , this  may not  be  too  large ? ,
Ringing  in  my  conventional Rx's  produces  a  very  wide 'slash'   over the  the  band  , it  was  only with the  $5  dongle  and the  'fast'  sdr-sharp  software , that  I spotted the  modulation  was  up-wards  ... !  with a  small   ATU , that  could  be  a  better Rx  method  , the  atu  being needed  to  remove the  local    3  carrier  MW station  , something  to  have a  go  at , when I  find  the  bench in the  shed .
Odd  that Joe's   signal  skipped over   the  UK last  night  ? 
73 -G..

Sent: Saturday, June 29, 2013 6:45 PM
Subject: Re: LF: VO1NA Op32 137.555 kHz

Hi Graham,
following your advice I've now taken out the SpecLab filter / noise blanker again. Not sure whether this will be for the better... anyway I'm aiming for a fair comparison of our two Opera reception methods.
Re DCF39: yes the space freq (139.17) is above the mark (138.83 kHz). But the biggest problem is the unfiltered FSK hardkeying, which (even at 325 km) produces annoying splatter down to about 136.6 kHz during each data telegram. That's almost 5 kHz occupied bandwidth for a 200 baud FSK signal! Should be completely inacceptable by any standard, but apparently fulfills specifications of their TRAM transmitter :-(
Best 73,
Markus (DF6NM)

From: Graham
Sent: Friday, June 28, 2013 11:42 PM
Subject: Re: LF: VO1NA Op32 137.555 kHz

Ok Marcus ,
Needs  must , I dont  think the   frequency  translation  would be  a  problem, but any modification  to the  envelope parameters  will  degrade  performance ,  the  low  s/n sdr  decodes  , point to  the  lack  of  'ringing'  in the  filters , enabling  much lower  levels , notably , using the  £5   dongle  in direct-sample  , I see  the  modulation  is  HF of the  carrier  , where  with  any  of the  conventional  Rx's  , there is a  splash  across  the  band .
Strange that  Iceland  has not  shown a  decode  , its about  1000  K  north  of the  direct  path and  half the  range ,    expected  ?
73 -G.
Sent: Friday, June 28, 2013 8:53 PM
Subject: Re: LF: VO1NA Op32 137.555 kHz

yes. I'm aware that Opera should nominally be fed with straight full-band SSB. But going by the first results, the preprocessing seemed to help a lot in the presence of our strong DCF splatters, so I left it in. In any case I'd need SL as an audio mixer to accomodate my fixed 135.5 kHz LO.
Best 73,
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