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10846Re: [wsjtgroup] multi decode same station

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  • Joe Subich, W4TV
    Jul 16, 2013
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      > I know it's not the sound card because I've been using SignaLink USB
      > for years now and it's never had multiple decodes of the same station
      > on the waterfall.

      Have you ever use JT9 before? The multiple decodes are well documented
      from the very beginning whilst other modes do not show that issue since
      their spectra are all more than 100/120 Hz wide which obscures the
      spurious sidebands.

      I can, and have, generated the issue with the inexpensive amateur sound
      cards on the bench. It is completely repeatable and easy to cure just
      by adding the recommended 2.3V regulator to the V/2 bus and increasing
      the filtering on the V(USB) line. Less than $2.00 in parts increases
      dynamic range (both lower noise floor and spurious removal) in those
      devices by 30 dB.

      73,

      ... Joe, W4TV


      On 7/16/2013 3:06 PM, digisignal@... wrote:
      > Hi Joe,
      >
      > I know it's not the sound card because I've been using SignaLink USB
      > for years now and it's never had multiple decodes of the same station
      > on the waterfall. I've been using WSJT programs, JT65-HF
      > programs,MultiPSK programs,WSPR programs, and none of them have ever
      > given a multiple decode of the same station on the waterfall.
      >
      > 73 Eddy N4ABN
      > On Tuesday, July 16, 2013 at 2:47 PM, "Joe Subich, W4TV" wrote:> It's
      > probably the software is in beta and hasn't got all the bugs
      >> worked out
      >
      > The software most certainly is not "at fault" - it is copying exactly
      > what it receives from the sound card. You will find that most of the
      > decodes show levels significantly below the "main" one - that is clear
      > indication that they are spurs generated either in the transmitter or
      > the receiver (sound card).
      >
      > These spurs have been noted since JT9 first appeared and simply do
      > not show up with other protocols because they are wide enough that
      > the "main" signal hides the spurs that fall within its passband.
      >
      > Any halfway competent technician can demonstrate the spurious
      > products approximately 40 to 45 dB below the desired signal generated
      > by these inexpensive sound devices ... similarly driving one of those
      > devices with a 4V P-P sine wave will clearly show the spurious receive
      > products when viewed with quality audio spectrum software. Instead of
      > 90+ dB spurious free dynamic range produced by a quality sound card,
      > these inexpensive products consistently demonstrate spurious products
      > around 40 dB relative to maximum output/maximum input and noise
      > limited
      > dynamic range (noise floor to maximum signal) in the low to mid 50 dB
      > category.
      >
      > 73,
      >
      > ... Joe, W4TV
      > On 7/16/2013 11:15 AM, digisignal@... wrote:
      >> Hi Joe,
      >>
      >> I can't believe it's my sound card because I've never seen it before
      >> on any of the other programs I use. It's probably the software is in
      >> beta and hasn't got all the bugs worked out of it and the sending
      >> station over driving.
      >>
      >> 73 Eddy N4ABN
      >>
      >> On Tuesday, July 16, 2013 at 9:27 AM, "Joe Subich, W4TV"
      >> wrote:Multiple decodes of the same station seem to occur only on
      > very
      >> strong
      >> signals (in most cases > +20) and are related either to hum on that
      >> station's signal or more likely to hum in the *receiving station's*
      >> sound card.
      >>
      >> There are certain inexpensive amateur sound card products that skip
      >> the
      >> V/2 reference regulator recommended by the sound chip manufacturer.
      >> The
      >> V/2 reference is also required for the op-amps used in the audio
      >> chains.
      >> Those same sound card products also lack sufficient filtering on the
      >> USB
      >> power line allowing the typical 2 x line frequency ripple to
      > modulate
      >> both transmit and receive audio.
      >>
      >> 73,
      >>
      >> ... Joe, W4TV
      >> On 7/16/2013 12:13 AM, digisignal@... wrote:
      >>> With WSJTX v1.1,r3459 I am getting multi decodes of the same
      >> station
      >>> sometimes. Stations must be transmitting harmonics? For example one
      >> of
      >>> the stations decode window shows 1440, 1460, 2100, 2662df all from
      >> the
      >>> same station. Is this a glitch in the program that hasn't been
      >> fixed
      >>> yet?
      >>> 73 Eddy N4ABN
      >>>
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