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Re: 7.035Mhz USB Q15X25 VK4AKP-1 PBBS Kam XL Please leave Test MSG.

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  • Charles Brabham
    Ken, can you adjust the parameters for a lower baud rate and have the modem scale down automatically, as previos Q15x25 implementations do? The reason I ask is
    Message 1 of 4 , Jul 31, 2007
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      Ken, can you adjust the parameters for a lower baud rate and have the
      modem scale down automatically, as previos Q15x25 implementations do?

      The reason I ask is that on the 17 meter Q15x25 ARRL SkipNet last year,
      we were operating with 14 PSK streams at 2300 baud because the narrower
      signal worked out a lot better with most HF rig's available passband.

      73,
      Charles Brabham, N5PVL
    • Ken
      Hi Charles. The answer to that is looking like yes. I say looking like because of the following. - The last Beta release allows for scaleing the modem between
      Message 2 of 4 , Jul 31, 2007
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        Hi Charles.

        The answer to that is looking like yes.

        I say looking like because of the following.

        - The last Beta release allows for scaleing the modem between
        1000-3000 Baud.
        - For some reason it will only talk to MixW on speeds 2200-3000. (No
        Lower). But I think I know why, and hopefuly Kantronics will be able
        to fix this.

        I am starting to learn a lot about running more complex modes on HF.

        It seems HF rig's generally suffer from a lot of problems when it
        comes to running these more advanced digital modes.

        - RF feedback / distortion is high on the list. RF gets back into the
        audio stream very easily and distorts the injected audio. Even with
        isolation transformers the ALC needs to be kept relativly low.

        - All isolation transformers are not created equal! LOL. The audio
        band pass characteristics vary greatly. The RX transformer I currently
        use for example is slicing off 50% of the lower end of the audio
        spectrum at 2300, 2400, 3000 speed settings.

        - Once again with RF distortion of the audio. Isolation of the
        antenna's feed line to the antenna can also help. As specially with
        vertical's.

        My next job is to find a reasonable source of isolation transformers
        that have a better audio band pass spec and build a new isolation
        interface.

        I'd also be interested to hear more about modes like DRM etc and how
        they have handled these sort of issues? Or wether the design of DRM
        gets around these issues some how?

        .-.-.

        --- In Q15X25@yahoogroups.com, "Charles Brabham" <n5pvl@...> wrote:
        >
        > Ken, can you adjust the parameters for a lower baud rate and have the
        > modem scale down automatically, as previos Q15x25 implementations do?
        >
        > The reason I ask is that on the 17 meter Q15x25 ARRL SkipNet last year,
        > we were operating with 14 PSK streams at 2300 baud because the narrower
        > signal worked out a lot better with most HF rig's available passband.
        >
        > 73,
        > Charles Brabham, N5PVL
        >
      • Charles Brabham
        I ran it like PSK31, with my rig s power turned all the way up. I control the power out by adjusting the audio level going in to the Mic plug, and/or use the
        Message 3 of 4 , Jul 31, 2007
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          I ran it like PSK31, with my rig's power turned all the way up.

          I control the power out by adjusting the audio level going in to the
          Mic plug, and/or use the Mic Gain control to adjust as high as I can
          with zero ALC activity.

          I usually ran about 50-60 watts, that way.

          Note that Q15x25 is not just an HF mode. I have found it to be better
          than Packet for mixed-mode digital operation over a VHF FM repeater,
          of all things. - It works very well at this!

          The only parameter you need to change is TXDELAY, which I had to set
          for 800ms. One repeater I tried required a full second ( 1000ms ) of
          delay in order to work.

          This gives you digital capability when needed on your voice repeater,
          at twice the speed of regular packet.

          The TXDELAY being so long does slow things down, but Q15x25 tends to
          large MAXFRAME and PACLEN values, so it all comes out in the wash as
          a very effective mixed-mode system for VHF/UHF.

          http://www.uspacket.org/mixmode.htm

          73,
          Charles Brabham, N5PVL
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