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Re: [tracker2] performance compared to d700?

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  • James Ewen
    ... Are the antenna gain figures the same? Are they at the same physical height? Are the feed line losses identical? Are the receiver sensitivities the same?
    Message 1 of 5 , May 2, 2008
      On Fri, May 2, 2008 at 5:06 PM, Robert Ellis <k5osx@...> wrote:


      > I was expecting that all the traffic reported by the OT2m
      > would be the same as with the d700. However, there's a
      > lot more traffic on the OT2m than there is on the d700.
      >
      > The antenna used with the tm-271 is a 20 year old 5/8 2m
      > antenna (larsen LM-MM). The antenna on the d700 is a dual
      > band comet, SBB5 with 3/5.5dB gain.
      >
      > Is the OT2m better able to decode aprs packets than the
      > d700? Or am I looking at the effects of using a dual band
      > antenna (eg, compromises to support 2 bands)?

      Are the antenna gain figures the same? Are they at the same physical
      height? Are the feed line losses identical? Are the receiver
      sensitivities the same?

      Like Jason says, you need to remove all the variables, and simply feed
      the audio to the two units. I might have to do that here for fun.
      Running the D700 and D710 in the same vehicle for a while, I noticed
      that they didn't always hear the same stations. The simple difference
      of one antenna being 4 feet further back on the roof of the van made a
      bit of difference on the signal path, and possibly the reflections.
      Feeding the same audio streams to both decoders will let you make
      comparisons between the decoding hardware without worrying about other
      variables.

      However, I have a feeling that the radios ignore incoming packets when
      displaying information on the screen. I have no quantitative proof,
      but just a gut feeling. I have my radio set up to interrupt the
      display to show the incoming packet. I'm sure I have heard a couple
      packets come in while a station's information is being displayed, but
      there's no update on the screen, and the last station in the list is
      the one that was displayed on the main screen.

      Now I live in an area where we normally see less than 240 packets per
      hour (http://members.shaw.ca/jewen/trafficlive.htm), so I don't get a
      lot of chance to see rapid incoming packets much...

      James
    • Bill Vodall WA7NWP
      ... Not really. The D700 use flat discriminator audio. Standard (what ever that is) 1200 baud ax25 packet has the standard audio pre/de-empasis... I
      Message 2 of 5 , May 2, 2008
        > > Is the OT2m better able to decode aprs packets than the
        > > d700? Or am I looking at the effects of using a dual band
        > > antenna (eg, compromises to support 2 bands)?
        >
        > Are the antenna gain figures the same? Are they at the same physical
        > height? Are the feed line losses identical? Are the receiver
        > sensitivities the same?
        >
        > Like Jason says, you need to remove all the variables, and simply feed
        > the audio to the two units. I might have to do that here for fun.
        > Running the D700 and D710 in the same vehicle for a while, I noticed
        > that they didn't always hear the same stations. The simple difference
        > of one antenna being 4 feet further back on the roof of the van made a
        > bit of difference on the signal path, and possibly the reflections.

        > Feeding the same audio streams to both decoders will let you make
        > comparisons between the decoding hardware without worrying about other
        > variables.


        Not really. The D700 use flat discriminator audio. "Standard" (what
        ever that is) 1200 baud ax25 packet has the standard audio
        pre/de-empasis... I would expect the D7wuds to be better with other
        similar rigs while speaker audio should be better with their similar
        rigs.

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

        73
        Bill - WA7NWP
      • 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 3 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
          deemphasis.

          > 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.

          James
          VE6SRV
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