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PSK ?

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  • Bernie
    As you will see, I am quite new to digital. One question I have is what is the difference between QPSK and BPSK. I use HRD and DM780 and when I open it up, how
    Message 1 of 6 , May 2, 2011
      As you will see, I am quite new to digital. One question I have is what is the difference between QPSK and BPSK. I use HRD and DM780 and when I open it up, how do I know which one to choose. Please excuse the "dumb" question but I have been confused by the choice.

      73 de Bernie - W8NBC
      SKCC#7783, 30MDG#3936
    • Dave Wright
      Bernie, When most people talk about PSK31, they are talking about BPSK31...that is the default PSK31. QPSK31 has some advantages in certain circumstances,
      Message 2 of 6 , May 2, 2011
        Bernie,

        When most people talk about PSK31, they are talking about BPSK31...that
        is the "default" PSK31.

        QPSK31 has some advantages in certain circumstances, but it is sideband
        specific (are you in USB or LSB?) while BPSK31 is not.

        If you start with BPSK, you should have no problems whatsoever.

        Dave Wright
        K3DCW

        "Real radio bounces off the sky"

        On 5/2/11 10:23 AM, Bernie wrote:
        > As you will see, I am quite new to digital. One question I have is what
        > is the difference between QPSK and BPSK. I use HRD and DM780 and when I
        > open it up, how do I know which one to choose. Please excuse the "dumb"
        > question but I have been confused by the choice.
        >
        > 73 de Bernie - W8NBC
        > SKCC#7783, 30MDG#3936
      • Bob N3PPH
        You will find by far more BPSK31 signals than QPSK31. A page you may want to check out just to see and hear many of the different modes
        Message 3 of 6 , May 2, 2011
          You will find by far more BPSK31 signals than QPSK31. A page you may want to check out just to see and hear many of the different modes http://www.w1hkj.com/FldigiHelp-3.20/Modes/index.htm.
          73,
          Bob N3PPH

          On 5/2/2011 10:23 AM, Bernie wrote:
           

          As you will see, I am quite new to digital. One question I have is what is the difference between QPSK and BPSK. I use HRD and DM780 and when I open it up, how do I know which one to choose. Please excuse the "dumb" question but I have been confused by the choice.

          73 de Bernie - W8NBC
          SKCC#7783, 30MDG#3936

        • Andy obrien
          And while on the subject of QPSK, here is an old article about PSK31 QPSK that I wrote around 2000 for the Logger32 help files, it includes quotes from Peter
          Message 4 of 6 , May 2, 2011
            And while on the subject of QPSK, here is an old article about PSK31
            QPSK that I wrote around 2000 for the Logger32 help files, it
            includes quotes from Peter Martinez that he granted permission for me
            to use .

            Andy K3UK



            QPSK (Quaternary Phase Shift Keying) Operation
            Andrew J. O'Brien, KB2EOQ

            QPSK is referred to as an error-correcting PSK mode. Strictly
            speaking, it is not error-correcting in the traditional sense, but
            we'll
            leave that for another discussion. You will find it very useful in
            copying very weak signals. You will also discover that it is used
            less than BPSK.
            The usual convention among QPSK'ers is to use BPSK to establish a QSO
            and then switch to QPSK You will rarely find someone
            calling CQ in QPSK mode. Some radio amateurs will switch to QPSK if a
            BPSK QSO with weak signals is producing poor copy.
            PSK veterans will point out, however, that while QPSK outperforms BPSK
            when weak signals are the issue, QPSK will perform no
            better than BPSK if noise is the signal limiting condition.
            In the ancient, early days of PSK31, in the last century, QPSK was
            used as the mode of choice for some PSK nets, but that does
            appear to be the case in the 21st century.
            .
            Tuning a QPSK Signal
            snip....

            QPSK can perform better than BPSK when band conditions are poor due to
            polar flutter. At such times you may be able to get
            copy from a QPSK signal even though the "cross" in the tuning window
            is poorly formed.
            Note: QPSK requires that BOTH stations in the QSO be using the same
            sideband! While this is not important for BPSK QSOs, it
            vital when using QPSK.

            QPSK-Reversed
            BPSK is demodulated the same way whether you are on upper or lower
            sideband. This is not true for QPSK, which operates
            like RTTY. You must shift the signal in a way that the decoder expects
            or it will not decode. In the case of QPSK, this leads to
            problems with standards, since the mode is so new.
            In actual practice, most hams appear to be operating BPSK using AFSK
            and upper sideband. This means that, when they switch
            QPSK (without reversing), they must be decoded by the other station
            using upper sideband and QPSK (without reversing).
            However, the standard of RTTY operation is lower sideband, and this
            means that most hams, operating as just mentioned, are
            operating QPSK-reverse, based on the RTTY standard.
            What this really means is that, when you and another station decide to
            switch to QPSK, if you do not know whether that station is
            using upper or lower sideband, there is a chance that you will not
            decode that station. If you click again on the mode pane, it will
            switch from QPSK to QPSK-reverse, and you should begin to copy.
            One trick is to set all three Rx windows on the signal to be copied,
            set one aux window at QPSK and the other at QPSK-reverse.
            When you see which Aux window starts to print readable copy, switch
            your main Rx window to that mode and you can then

            So What Is QPSK? How QPSK Got Its Name
            Peter, G3PLX, says in an article entitled "PSK-31, A new
            radio-teletype mode with a traditional philosophy," says that he
            called it
            "quadrature polarity reversal keying" (which of course would have come
            out as QPRK), but that everyone else calls it quaternary
            phase-shift keying (QPSK). It is an error-correcting mode that relies
            on four phase-shifts rather than two, to create the basic
            scheme.

            Peter Martinez' (G3PLX) Description of QPSK
            The QPSK mode used in PSK31 takes the binary data-stream, at the point
            where it would otherwise go direct to the BPSK
            modulator, and feeds that through a 5-bit shift-register. A logic
            operation then forms the parity function of the 1st, 2nd, and 5th
            stages, and another forms the parity function of the 1st, 3rd, and
            5th, giving two bit-streams at the same 31.25 bps rate as the
            original data. These two bits form a binary number, the four values of
            which are mapped to the four possible phase-shifts in the
            QPSK modulation. Thus a single data-bit from the source results in a
            5-bit-long predictable sequence of 90-degree and 180
            phase-shifts, interleaved with those of following and preceding bits.
            In the receiver, a Viterbi decoder is used to keep track of all 32
            possible combinations of guesses at the transmitted datastream,
            a running total of how well the received pattern of phase-shifts
            matches each guess. The clever thing about the Viterbi decoder is
            that it can be sure that if it throws out the worst 16 guesses before
            it receives the next signal (which doubles the number of
            to 32 again), it can never get it wrong, and after about 20 more
            signals, it can be pretty certain that its guess 20 signals ago was
            right. The snag is that it can only output its best guess after a
            delay of 20 signals, or 640mS in the case of PSK31. Longer Viterbi
            decoders are possible, but the amount of computation doubles at each
            extra signal delay, and for PSK31, which is used for live
            QSOs, the delay would be too long.
            More Facts to Consider About QPSK
            The relationship between BPSK and QPSK is that both have the same
            bandwidth, but that QPSK uses that bandwidth for two
            signals, shifted-from each other by 90 degrees. The extra signal is
            used to transmit redundant information for error-correction.
            reduces the signal-to-noise ratio for QPSK by 3 dB, in comparison to
            BPSK. The expectation is that the error-correction will more
            than make up for this difference. The results are not in, and one goal
            of current PSK31 activity is to evaluate and compare BPSK
            QPSK, to determine the situations in which each method is superior.
            According to Peter, BPSK should be superior under conditions of
            ordinary noise (white noise or random noise) but that under
            conditions of fading or real-life interference (as contrasted with
            random white noise), QPSK may be superior. More evaluation is
            needed.
            For a good introduction see NB6Z's excellent discussion of QPSK at
            http://www.teleport.com/~nb6z/psk31.htm.
            *Peter Martinez has granted Logger32 permission to use his above description


            On Mon, May 2, 2011 at 10:30 AM, Bob N3PPH <rsheskin@...> wrote:
             

            You will find by far more BPSK31 signals than QPSK31. A page you may want to check out just to see and hear many of the different modes http://www.w1hkj.com/FldigiHelp-3.20/Modes/index.htm.

            73,
            Bob N3PPH

            On 5/2/2011 10:23 AM, Bernie wrote:
             

            As you will see, I am quite new to digital. One question I have is what is the difference between QPSK and BPSK. I use HRD and DM780 and when I open it up, how do I know which one to choose. Please excuse the "dumb" question but I have been confused by the choice.

            73 de Bernie - W8NBC
            SKCC#7783, 30MDG#3936


          • Bernie Hildebrand
            Andy Thank you for the very understandable description. Your help is very much appreciated. 73 de Bernie - W8NBC SKCC#7783, DMC#3936 30MDG#4835
            Message 5 of 6 , May 2, 2011
              Andy
              Thank you for the very understandable description. Your help is very much appreciated.

              73 de Bernie - W8NBC
              SKCC#7783, DMC#3936
              30MDG#4835
            • Siegfried Jackstien
              Bpsk shifts phase between 0 and 180 and back Qpsk knows also 90 and 270 degrees in the phase switching ... that is why it is sideband sensitive Dg9bfc Sigi Ps
              Message 6 of 6 , May 2, 2011
                Bpsk shifts phase between 0 and 180 and back
                Qpsk knows also 90 and 270 degrees in the phase switching ... that is why it
                is sideband sensitive
                Dg9bfc
                Sigi
                Ps most what you will find is bpsk31 (almost standard) and some bpsk63
                I never found a qpsk station on air ... I think some use it after asking
                qsp-partner to switch ... but do not know really

                > -----Ursprüngliche Nachricht-----
                > Von: 30MDG@yahoogroups.com [mailto:30MDG@yahoogroups.com] Im Auftrag von
                > Bernie
                > Gesendet: Montag, 2. Mai 2011 14:24
                > An: 30MDG@yahoogroups.com
                > Betreff: [30MDG] PSK ?
                >
                >
                >
                > As you will see, I am quite new to digital. One question I have is what is
                > the difference between QPSK and BPSK. I use HRD and DM780 and when I open
                > it up, how do I know which one to choose. Please excuse the "dumb"
                > question but I have been confused by the choice.
                >
                > 73 de Bernie - W8NBC
                > SKCC#7783, 30MDG#3936
                >
                >
                >
                >
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