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Re: [tracker2] performance compared to d700?

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  • James Ewen
    ... In 9600 baud mode... In a D700 to D700 system, you could call that flat . The D700 s in 1200 baud mode use preemphasized/deemphasized audio, which again
    Message 1 of 5 , May 3, 2008
      On Fri, May 2, 2008 at 10:55 PM, Bill Vodall WA7NWP <wa7nwp@...> wrote:

      > The D700 use flat discriminator audio.

      In 9600 baud mode... In a D700 to D700 system, you could call that "flat".

      The D700's in 1200 baud mode use preemphasized/deemphasized audio,
      which again can be called "flat".

      If you are pulling 1200 baud audio directly from the discriminator
      audio, it should have 6 db per octave preemphasis which was added at
      the transmitter. You need to undo what was done at the transmitter to
      get back to a "flat" response.

      > "Standard" (what
      > ever that is) 1200 baud ax25 packet has the standard audio
      > pre/de-empasis...

      I'll agree with that definition, which means that you have to inject
      audio before the preemphasis filter in the transmitter, and pull it
      out after the deemphasis filter in the receiver. Doing one, and not
      the other leads to tinny sounding audio with preemphasis left in
      place, or muddy sounding audio with high end roll off due to extra

      > I would expect the D7wuds to be better with other
      > similar rigs while speaker audio should be better with their similar
      > rigs.

      Well, according to the D700 service manual, 1200 bps packet signals
      are directed to IC801, the mic amp, which in turn is fed to Q801 and
      Q802, the preemphasis circuit. 9600 bps packet signals are injected
      into IC802, the tone amp, which bypasses the preemphasis circuit.

      On reception, deemphasized audio is sent to the PR1 pin, while PR9
      will have audio that is not deemphasized.

      The built-in TNC has it's own deemphasis circuit, and is fed
      non-deemphasized audio. Buffer circuits through Q5 or Q6 are selected
      based on whether the TNC is in 1200 or 9600 mode.

      Now the question that I can't find an answer to in the service manual,
      is whether you can have a signal available at PR1, and have the
      internal TNC enabled at the same time. The cross point switch IC702
      might not be able to be configured that way. I haven't played enough.

      > FWIW - flat audio is better, but standard is better then better...

      Depending on your definition of flat audio, and what it is you are
      trying to do. 1200 baud should make use of the preemphasis and
      deemphasis circuits, while 9600 baud should be injected after
      preemphasis, and picked off before deemphasis. Both of these scenarios
      see a flat frequency response, it's only when you mix and (mis)match
      where you start seeing problems.

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