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Re: JT9-1 no decode on very strong signal why?

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  • booz2m
    Hello Philip It is hard for me to tell the exact reason why but I will give it a go anyway it if is not pure overloading or a timing issue. You and Michel,
    Message 1 of 4 , Jun 14, 2013
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      Hello Philip

      It is hard for me to tell the exact reason why but I will give it a go anyway it if is not pure overloading or a timing issue.

      You and Michel, F1ABL, are about 1300 km apart and with several major airports in between (BHX, LGW, LHR, CDG and ORY) thus with lots of aircraft scatter possibilities. This may have caused a lot of multi path on top of the direct signal.

      It could also have been other phenomenons that caused the tight tone spacing in JT9-1, <2 Hz, to challenge the decoder when perhaps the multi path made the tones jump 10 Hz or more.

      I had a chat with Jim, VE1JF, the other week on the ON4KST 50/70 MHz chat. Jim is fairly active on 6 m with JT9-1. He said that he often experience signals to be visible in the waterfall yet they fail to decode. I suggested him to try JT4 or JT65 that both have "much" wider tone spacing then JT9. On the VUSHF bands path irregularities often distort the signal one way or the other. I believe that this is what you are experiencing. JT9 with its narrow tone spacing is not very robust to VUSHF paths. I acknowledge the challenge of till trying to see if JT9 will work given the circumstances. This is what ham radio is all about. Just like trying to land a marlin with an ultra thin fishing line.

      If you want to dig more into path issues you can try to listen for OZ7IGY. It transmit a mixed mode signal in a one minute cycle (PI4, CW and carrier). See more here: http://rudius.net/oz7igy The PI4 modulation is a cousin of JT4, JT9 and WSPR and like JT4F/G it has a wide tone spacing of about 234 Hz.

      73
      Bo, OZ2M
    • John
      Hi Philip Yes, I find the same thing. JT9 was ofcourse designed for very weak signals, and mainly on HF. A typical Es signal can fluctuate from just detectable
      Message 2 of 4 , Jun 15, 2013
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        Hi Philip

        Yes, I find the same thing.

        JT9 was ofcourse designed for very weak signals, and mainly on HF.
        A typical Es signal can fluctuate from just detectable to massive,
        so a very large dynamic range is required.

        Any multipath, scattering or meteor reflection well cause doppler spread, and there can be plenty of multipath with short skip sporadicE signals.

        6M will also be more critical than HF regarding frequency stability and drift

        John
        GW4MBN


        --- In wsjtgroup@yahoogroups.com, "Philip" <G0isw@...> wrote:
        >
        > Hello all,
        >
        > I'm having great fun with JT9-1 on 50MHz, thanks again Joe.
        >
        > Today I had an unusual finding I was called by my friend Michel F1ABL who had a really strong signal +11dB and more, I could hear him clearly and see his trace perfectly, but I simply couldn't decode him although I was decoding weaker signals from other stations.
        >
        > We are both using Dimension 4 for our clocks and latest version of WSJT-X.
        >
        > By chance I reduced my 'digital gain for audio input' slider from its normal no signal 30dB level to almost nothing and then the decodes began to work.
        >
        > Does this mean that I have to do this every time there is a really strong signal? Is this normal and happens to others because the software is expecting a weak signal?
        >
        > Just trying to understand better.
        >
        > 73 de Philip G0ISW
        >
      • k0og
        I have found the same thing occasionally, and found that if I reduce the line-in fader in Windows to reduce the apparent signal strength to the software, it
        Message 3 of 4 , Jun 15, 2013
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          I have found the same thing occasionally, and found that if I reduce the line-in fader in Windows to reduce the apparent signal strength to the software, it will begin decoding.

          73,
          -Joe-

          --- In wsjtgroup@yahoogroups.com, "John" <tonquedec@...> wrote:
          >
          > Hi Philip
          >
          > Yes, I find the same thing.
          >
          > JT9 was ofcourse designed for very weak signals, and mainly on HF.
          > A typical Es signal can fluctuate from just detectable to massive,
          > so a very large dynamic range is required.
          >
          > Any multipath, scattering or meteor reflection well cause doppler spread, and there can be plenty of multipath with short skip sporadicE signals.
          >
          > 6M will also be more critical than HF regarding frequency stability and drift
          >
          > John
          > GW4MBN
          >
          >
          > --- In wsjtgroup@yahoogroups.com, "Philip" <G0isw@> wrote:
          > >
          > > Hello all,
          > >
          > > I'm having great fun with JT9-1 on 50MHz, thanks again Joe.
          > >
          > > Today I had an unusual finding I was called by my friend Michel F1ABL who had a really strong signal +11dB and more, I could hear him clearly and see his trace perfectly, but I simply couldn't decode him although I was decoding weaker signals from other stations.
          > >
          > > We are both using Dimension 4 for our clocks and latest version of WSJT-X.
          > >
          > > By chance I reduced my 'digital gain for audio input' slider from its normal no signal 30dB level to almost nothing and then the decodes began to work.
          > >
          > > Does this mean that I have to do this every time there is a really strong signal? Is this normal and happens to others because the software is expecting a weak signal?
          > >
          > > Just trying to understand better.
          > >
          > > 73 de Philip G0ISW
          > >
          >
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