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Re: [tracker2] performance compared to d700?

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  • Jason KG4WSV
    If you really want to eliminate the variables, take the audio output of the D700 and feed it to the T2 (leaving the D700 TNC on, of course). Once you ve got
    Message 1 of 5 , May 2, 2008
      If you really want to eliminate the variables, take the audio output
      of the D700 and feed it to the T2 (leaving the D700 TNC on, of
      course). Once you've got it adjusted, you've got the same RF rig, and
      it's all down to the TNCs.

      I'd be curious to see the results.

      -Jason
      kg4wsv
    • 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 2 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 3 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 4 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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