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Re: Status of Q15X25?

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  • Stewart
    GM, Rick - I appreciated your response and will interspace my responses below. To be kept in mind is that MARS operates in a cleaner environment then is
    Message 1 of 33 , Nov 16, 2004
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      GM, Rick -

      I appreciated your response and will interspace my responses below.
      To be kept in mind is that MARS operates in a "cleaner" environment
      then is often available on amateur freqs, which situation can affect
      results.

      --- In Q15X25@yahoogroups.com, "Rick Williams" <mrfarm@m...> wrote:
      >
      > Stewart, W1UVE wrote:
      >
      > >>>>> A major objective has been to use and evaluate
      > SC software for possible use within MARS. Because of the apparent
      > superiority of MT63, we did an exhaustive study of it over a period
      > of two months and prepared a formal report of our results.
      >
      > =====
      >
      > This report did not seem to compare MT63 to MFSK16. Have you done
      such a comparison later on and still found MT63 to be superior to
      MFSK16? Particularly, in terms of getting the message through under
      less than ideal conditions?

      At the time of the study we were mainly interested with the question
      of how best to get traffic through - Reliability consistant with
      Security and Speed being our goal and basic to MARS communications.
      The conclusions re MFSK arose from a number of tests over time, our
      conclusions about which we feel are correct. Obviously, MFSK is not
      designed for speedy communications.

      To encapsulate our thoughts on MT63, based on consistant use over two
      years, there is nothing that has touched it when conditions have
      deteriorated to the point that other modes have dropped out of sight.
      It is not unusual to be receiving solid copy on the screen and not
      see anything on the waterfall or hear anything from the speaker. P-
      III, let alone any other mode, as good as it is, does not appear to
      match MT63 down in the trenches. I would further add that, especially
      over the past year, we have found it necessary to more and more
      complete our nets using MT63 because of propagation changing during
      the net. I believe it is safe to observe that this situation is going
      be continuing for the next 4-5 years until we reach the begining of
      the upward slope of the 11 year cycle.

      > The ability to use MT63 and voice simultaneously would not be as
      practical with MFSK16 although in order to do this, wouldn't you have
      to have signals well above the noise?

      My comments here simply reflect our experiences/testing over time.
      They are not based on scientific measurements. In short, if voice
      comms are possible then simultanious transmissions as described are
      invariably possible. Parenthetically, this particular phenomenon was,
      by chance, originally called to my attention by a MARS member on the
      West coast where they had been playing with it. We have simply
      verified it.

      > You did indicate that MFSK is a good choice but hard to lock in on.
      Maybe it is me, but when I use Hamscope, it only takes a few seconds
      to lock in. All you have to do is bridge across the pattern on the
      waterfall so the markers straddle it and it seems to lock right in.

      I will not dispute this since we have never pursued this particular
      aspect of the subject. However, to be considered is that it takes
      time to switch programs. It would not appear to make sense to switch
      to Hamscope simply to do some kb-to-kb, then switch out to another
      mode to send traffic, and then switch back again, given the time
      factor involved.

      > >>>>> - QPSK63 (not 31) appears to be a very good alternative. It
      is at least as robust as MFSK, if not more so.
      > =====
      > Do others find this true? This seems unlikely to me.

      Interesting question as we have only recently begin to study it as it
      relates to finding an alternative to MT63 kb-to-kb. The initial
      consensus by members, though, is that QPSK63 is a more robust mode,
      the exact degree of which might be open to question. Additionally to
      be considered is that QPSK63 throughput speed is noticeably (modestly)
      higher than that of MFSK, hence a message of given length should take
      less hits then if sent by MFSK.

      Incidentally, if you are interested, there is an excellent
      implementation of an ARQ application of QPSK63 to be found at:
      http://www.w1fn.org FNpsk, a freeware program, effectively
      automates the conduct of a digital net to a very high degree.

      > 73,

      > Rick, KV9U

      I have enjoyed this chat and look forward to reading further Posts
      from you in the future.

      73,

      Stewart NNN0STE W1UVE
    • Stewart
      GE, Rick - I guess all I can say is that the proof is in the the pudding and my comments are based on experience, which after should be the ultimate test.
      Message 33 of 33 , Nov 17, 2004
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        GE, Rick -

        I guess all I can say is that the proof is in the the pudding and my
        comments are based on experience, which after should be the ultimate
        test. Incidentally, I would add that we do re-review programs that
        had been looked at previously.

        What has to be remembered is that MARS stations are not concerned
        with going around the world point-to-point. Our nets generally
        involve distances of 200 to 300 miles, give or take, although there
        are nets that do cover a much larger area and can require the use of
        relays to get some stations checked in. Additionally, we are
        essentially using clear channels and formal net procedures, hence we
        are generally not bogged down with QRM, deliberate or otherwise.
        Additionally, we have a number of channels available such that for
        part of the year we will use one frequency for a given net, and move
        2 or 3 or 4 MHz for the rest of the year, recognizing the seasonal
        changes in propagation.

        I have no particular quarrel with your comments about PACTOR.
        However, because it is an ARQ mode, when conditions go south, the
        ACKing and NAKing can really stretch out the time to send a message.
        Taking 20 minutes or more to send one message, even though it will be
        complete, seems to me not to make much sense and certainly ties up a
        frequency unnecessarily.

        I can sympathize, and agree, with your plaint about so many modes and
        finding someone to talk with. Fortunately, for me. if a new mode
        comes along we will take the opportunity to look at it on one of our
        digital nets, and then whatever happens will happen as far as what we
        do with it. If some of us want to look at it further, we will simply
        set up a sked and do so at a time of our convenience.

        With respect to FNpsk, I only know was is found on the referenced web
        site. I personally am not aware of any dedicated reflectors at this
        point in time, although that is not to say one doesn't exist.

        Finally, with respect to "lab" testing, it is essential for the
        development of software. However, as long as one does not disregard
        new advances, the old axiom about "not fixing something that works"
        is still valid.

        73,

        Stewart NNN0STE W1UVE


        --- In Q15X25@yahoogroups.com, "Rick Williams" <mrfarm@m...> wrote:
        >
        > Stewart wrote:
        >
        > >>>>> To encapsulate our thoughts on MT63, based on consistant use
        over two
        > years, there is nothing that has touched it when conditions have
        > deteriorated to the point that other modes have dropped out of
        sight.
        > It is not unusual to be receiving solid copy on the screen and not
        > see anything on the waterfall or hear anything from the speaker. P-
        > III, let alone any other mode, as good as it is, does not appear to
        > match MT63 down in the trenches.
        >
        > =====
        >
        > I wonder why your experiences are so different from the actual
        tests done
        > with measuring how deep into the noise MFSK16 and other modes are
        able to do
        > compared with MT63?
        >
        > Of all the modes MT63 is about the worst in terms of weak signals!
        >
        > Pactor is really very good and my understanding is that it works
        well below
        > what some have claimed at only -5 db S/N.
        >
        > But I think the largest factor for MARS is that MT63 is able to TX
        much
        > faster data rates due to the huge BW. Many times larger than most
        of the
        > other digital modes. This works OK on a voice channel but not so
        good for
        > spectrum conservation.
        >
        > One thing that MT63 does extremely well is handle multipath and if
        you are
        > often using NVIS, you will encounter this phenomenon to a greater
        degree
        > than longer distance TX. Is it possible that this may be another
        reason for
        > the apparent success of MT63?
        >
        > >>>> Incidentally, if you are interested, there is an excellent
        > implementation of an ARQ application of QPSK63 to be found at:
        > http://www.w1fn.org FNpsk, a freeware program, effectively
        > automates the conduct of a digital net to a very high degree.
        >
        > ======
        >
        > This is completely new to me and have not seen this before. Any
        others here
        > finding this to work well?
        >
        > Is there a list or group that discusses this mode?
        >
        >
        > What is happening though is that there are so many modes, and so
        few digital
        > operators of these modes, that you rarely find anyone else to
        connect with.
        > For example, I have tried MT63 on 30 and 40 meters with no luck
        finding
        > anyone else. With a more commonly used mode, such as PSK31, it is
        much
        > easier to find someone.
        >
        > 73,
        >
        > Rick, KV9U
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