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10852Re: [wsjtgroup] multi decode same station

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  • Joe Subich, W4TV
    Jul 16 7:33 PM
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      > Where do you get this information?

      I get the information on the USB sound chips needing the V/2 regulator
      and a certain level of filtering on the V(usb) supply from the data
      sheet on the USB sound chips. I determine whether the correct parts
      are used in the design of a given product by studying the schematic for
      the device or studying the device itself. I determine the level of
      performance (noise floor, maximum signal capacity, and spurious free
      dynamic range by actually measuring those values on the bench).

      There are high quality devices that can be found for relatively low
      prices and there are poor quality devices at both high and low price
      points.

      I am not "naming names" but if any device lacks the V/2 regulator and
      has insufficient filtering on the V(usb) line, it will have a poor
      spurious dynamic range.

      73,

      ... Joe, W4TV


      On 7/16/2013 9:50 PM, digisignal@... wrote:
      > Joe,
      >
      > I went to the tigertronics web site which sells SignaLink USB and
      > there's nothing on there about a regulator add on for the device. Also
      > nothing on there about the filter cap you're talking about. Where do
      > you get this information?
      >
      > 73 Eddy N4ABN
      > On Tuesday, July 16, 2013 at 8:14 PM, "Joe Subich, W4TV" wrote:> I
      > believe he was over driving his output because his signal db was
      >> 10+ and more.
      >
      > +10 dB doesn't mean the other station was over driving his transmitter
      > - and you don't get multiple decodes from overdrive unless the audio
      > is so strong that *garbage in your sound card* modulates that incoming
      > signal and you see the resulting products. I regularly copy signals
      > at +20 or more that are absolutely clean because my sound card is
      > clean and does not create spurious products with strong signals.
      >
      > Stations that overdrive the audio input of their rig typically have
      > harmonics (particularly if they are in the lower half of the JT65A
      > spectrum) that can't be decoded and very strange "rough" sounding
      > audio - like the square wave they are in fact generating. JT65 and
      > JT9 are singe tone modulations and can be run into RF clipping without
      > causing IMD like is the case with PSK31 or other multi-tone modes.
      >
      > Again, when you see the multiple decodes, I'm sure you will find one
      > that is > +10 and the others are around -20 or somewhat less. That
      > 35 to 40 dB difference is the spurious dynamic range of *your* sound
      > card.
      >
      > > Are you talking about installing a regulator inside of the
      > SignaLink?
      >
      > I'm talking about installing the manufacturer recommended regulator on
      > the V/2 reference for any USB sound device that lacks it. I'm also
      > talking about increasing the filter cap on the V(USB) line ... many
      > inexpensive USB sound devices lack them although price is not always
      > a clue. I've seen the regulator in $19 USB sound dongles and I've
      > seen none in $150 devices.
      >
      > 73,
      >
      > ... Joe, W4TV
      > On 7/16/2013 6:10 PM, digisignal@... wrote:
      >> Joe,
      >>
      >> Yes I've used JT9 before. I've only started using it daily for a
      >> couple of days now. The multiple decode happened from the same
      > station
      >> a couple of times. He moved on the waterfall a few different places
      >> and each time he decoded several times in one sequence. I believe he
      >> was over driving his output because his signal db was 10+ and more.
      >>
      >> Are you talking about installing a regulator inside of the
      > SignaLink?
      >> I've got the paper work on it in a drawer somewhere. I'm not sure I
      >> could find it. Probably would have to look it up on the net.
      >>
      >> 73 Eddy N4ABN
      >> On Tuesday, July 16, 2013 at 5:59 PM, "Joe Subich, W4TV" wrote:> 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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