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13032Re: [wsjtgroup] JT9 use on 6 meters

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  • Joe Taylor
    Jul 30, 2014
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      Hi Jay,

      KA9CFD wrote:
      > I tried using JT9 on 6 meters today with not much luck. I was
      > seeing J69DS trace easily on the waterfall but just a couple
      > of decodes. The problem appears to be a slight receiver drift
      > in my Yaesu FT2000. I was wondering if it is possible to
      > introduce an AFC button for JT9 operation that would lock
      > on to the trace that you are trying to receive and compensate
      > for any radio drift? I am using WSJT-X ver. 1.3, r3673. If
      > there is a more recent version, I would like a link to it.

      It's hardly accidental that the docs explain that JT9 was designed for
      the LF, MF, and HF bands. Even 10 m is s stretch, with some radios and
      some propagation conditions.

      Like JT65, the JT9 decoder does have an AFC as part of its bag of
      tricks. It's always engaged, solving for a linear frequency drift term
      before decoding is attempted. The algorithm can perhaps be improved.
      It's a tougher job with JT9 than with JT65 -- not least, because the JT9
      protocol devotes only about half as much time to a synchronizing tone,
      compared with JT65.

      Much better to use JT65A on 6 meters; the extra-narrow bandwidth of JT9
      is hardly needed on 6, anyway.

      -- 73, Joe, K1JT
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