Loading ...
Sorry, an error occurred while loading the content.

Re: [wsjtgroup] An observed Sig-Rep I made btw JT65 & JT9

Expand Messages
  • Kai
    Hi Bob, I took a peek at Joe Taylor s WSJT user s guide. JT9 tones are just 0.58 Hz in duration, so the noise bandwidth is 1/0.58 = 1.7 Hz BW. JT65 tones are
    Message 1 of 12 , Sep 13, 2013
    View Source
    • 0 Attachment
      Hi Bob,
      I took a peek at Joe Taylor's WSJT user's guide. JT9 tones are just 0.58 Hz in duration, so the noise bandwidth is 1/0.58 = 1.7 Hz BW.
      JT65 tones are 0.372 s in duration so the noise bandwidth is 2.7 Hz. So just on the basis of noise bandwidth JT9 would operate at
      20log(2.7/1.7) = 2 dB better S/N ratio.  All straight out of Joe Taylor's documentation.
      Improvements in the decoding software increase that even more.

      I think that your observations are valuable confirmation of the improved S/N performance of JT9 relative to JT65.

      73
      Kai, KE4PT

      On 9/13/2013 8:26 AM, KD7YZ Bob wrote:
      Hey WSJT Group:
      
      Just an FYI (or FWIW) I just noted. 
      
      On the morning 30m path to VK3AMA, I saw a report of -18 when I was on JT65.
      4m later I see a report of -14 when I'd just switched to JT9.
      
      My impressions were that JT9, for me, was more sensitive. Obviously this
      is not even close to a scientific experiment, however.
      
      Still though, pretty neat on 1 watt with a ladder-line-fed 270-foot
      dipole at 80 feet up.
      
      
    • Kai
      Correction ... JT9 tones are just 0.58 seconds in duration Additionally Joe Taylor states that JT9 threshold sensitivity is -27 dB SNR, while JT65 is -24 dN
      Message 2 of 12 , Sep 13, 2013
      View Source
      • 0 Attachment
        Correction ... "JT9 tones are just 0.58 seconds in duration"

        Additionally Joe Taylor states that JT9 threshold sensitivity is -27 dB SNR, while JT65 is -24 dN SNR both in reference 2500 Hz BW.
        -Kai, KE4PT

        On 9/13/2013 11:04 AM, Kai wrote:
        Hi Bob,
        I took a peek at Joe Taylor's WSJT user's guide. JT9 tones are just 0.58 Hz in duration, so the noise bandwidth is 1/0.58 = 1.7 Hz BW.
        JT65 tones are 0.372 s in duration so the noise bandwidth is 2.7 Hz. So just on the basis of noise bandwidth JT9 would operate at
        20log(2.7/1.7) = 2 dB better S/N ratio.  All straight out of Joe Taylor's documentation.
        Improvements in the decoding software increase that even more.

        I think that your observations are valuable confirmation of the improved S/N performance of JT9 relative to JT65.

        73
        Kai, KE4PT

        On 9/13/2013 8:26 AM, KD7YZ Bob wrote:
        Hey WSJT Group:
        
        Just an FYI (or FWIW) I just noted. 
        
        On the morning 30m path to VK3AMA, I saw a report of -18 when I was on JT65.
        4m later I see a report of -14 when I'd just switched to JT9.
        
        My impressions were that JT9, for me, was more sensitive. Obviously this
        is not even close to a scientific experiment, however.
        
        Still though, pretty neat on 1 watt with a ladder-line-fed 270-foot
        dipole at 80 feet up.
        
        
      • Joe Subich, W4TV
        While 2dB applies to the tone duration, the over all bandwidth difference between a JT65A signal and a JT9-1 signal is more than 10 to 1 (~175 Hz vs. ~16 Hz).
        Message 3 of 12 , Sep 13, 2013
        View Source
        • 0 Attachment
          While 2dB applies to the tone duration, the over all bandwidth
          difference between a JT65A signal and a JT9-1 signal is more than
          10 to 1 (~175 Hz vs. ~16 Hz). That would imply a greater high
          bound on the difference in sensitivity - somewhere in the 11 dB
          range.

          I'm sure the real difference is somewhere between 2 dB (individual
          tone bandwidth) and 11 dB (occupied spectrum) ... 4 to 6 dB seems
          to be consistent with observed differences on HF paths.

          73,

          ... Joe, W4TV


          On 9/13/2013 11:39 AM, Kai wrote:
          > Correction ... "JT9 tones are just 0.58 seconds in duration"
          >
          > Additionally Joe Taylor states that JT9 threshold sensitivity is -27 dB
          > SNR, while JT65 is -24 dN SNR both in reference 2500 Hz BW.
          > -Kai, KE4PT
          >
          > On 9/13/2013 11:04 AM, Kai wrote:
          >>
          >>
          >> Hi Bob,
          >> I took a peek at Joe Taylor's WSJT user's guide. JT9 tones are just
          >> 0.58 Hz in duration, so the noise bandwidth is 1/0.58 = 1.7 Hz BW.
          >> JT65 tones are 0.372 s in duration so the noise bandwidth is 2.7 Hz.
          >> So just on the basis of noise bandwidth JT9 would operate at
          >> 20log(2.7/1.7) = 2 dB better S/N ratio. All straight out of Joe
          >> Taylor's documentation.
          >> Improvements in the decoding software increase that even more.
          >>
          >> I think that your observations are valuable confirmation of the
          >> improved S/N performance of JT9 relative to JT65.
          >>
          >> 73
          >> Kai, KE4PT
          >>
          >> On 9/13/2013 8:26 AM, KD7YZ Bob wrote:
          >>> Hey WSJT Group:
          >>>
          >>> Just an FYI (or FWIW) I just noted.
          >>>
          >>> On the morning 30m path to VK3AMA, I saw a report of -18 when I was
          >>> on JT65.
          >>> 4m later I see a report of -14 when I'd just switched to JT9.
          >>>
          >>> My impressions were that JT9, for me, was more sensitive. Obviously this
          >>> is not even close to a scientific experiment, however.
          >>>
          >>> Still though, pretty neat on 1 watt with a ladder-line-fed 270-foot
          >>> dipole at 80 feet up.
          >>>
          >>
          >>
          >>
          >
        • Rudy Benner
          The problem with JT9 is that it does not sound so cool as JT65, the almighty cool factor. r From: Joe Subich, W4TV Sent: Friday, September 13, 2013 12:30 PM
          Message 4 of 12 , Sep 13, 2013
          View Source
          • 0 Attachment
            The problem with JT9 is that it does not sound so cool as JT65, the almighty cool factor.
             
            r
             
            Sent: Friday, September 13, 2013 12:30 PM
            Subject: Re: [wsjtgroup] An observed Sig-Rep I made btw JT65 & JT9
             
             


            While 2dB applies to the tone duration, the over all bandwidth
            difference between a JT65A signal and a JT9-1 signal is more than
            10 to 1 (~175 Hz vs. ~16 Hz). That would imply a greater high
            bound on the difference in sensitivity - somewhere in the 11 dB
            range.

            I'm sure the real difference is somewhere between 2 dB (individual
            tone bandwidth) and 11 dB (occupied spectrum) ... 4 to 6 dB seems
            to be consistent with observed differences on HF paths.

            73,

            ... Joe, W4TV

            On 9/13/2013 11:39 AM, Kai wrote:

            > Correction ... "JT9 tones are just 0.58
            seconds in duration"
            >
            > Additionally Joe Taylor states that JT9
            threshold sensitivity is -27 dB
            > SNR, while JT65 is -24 dN SNR both in
            reference 2500 Hz BW.
            > -Kai, KE4PT
            >
            > On 9/13/2013 11:04 AM,
            Kai wrote:
            >>
            >>
            >> Hi Bob,
            >> I took a peek
            at Joe Taylor's WSJT user's guide. JT9 tones are just
            >> 0.58 Hz in
            duration, so the noise bandwidth is 1/0.58 = 1.7 Hz BW.
            >> JT65 tones
            are 0.372 s in duration so the noise bandwidth is 2.7 Hz.
            >> So just on
            the basis of noise bandwidth JT9 would operate at
            >> 20log(2.7/1.7) = 2
            dB better S/N ratio. All straight out of Joe
            >> Taylor's
            documentation.
            >> Improvements in the decoding software increase that
            even more.
            >>
            >> I think that your observations are valuable
            confirmation of the
            >> improved S/N performance of JT9 relative to
            JT65.
            >>
            >> 73
            >> Kai, KE4PT
            >>
            >> On 9/13/2013 8:26 AM, KD7YZ Bob wrote:
            >>> Hey WSJT Group:
            >>>
            >>> Just an FYI (or FWIW) I just noted.
            >>>
            >>> On the morning 30m path to VK3AMA, I saw a report of -18 when I was
            >>> on JT65.
            >>> 4m later I see a report of -14 when I'd just switched to JT9.
            >>>
            >>> My impressions were that JT9, for me, was more sensitive. Obviously this
            >>> is not even close to a scientific experiment, however.
            >>>
            >>> Still though, pretty neat on 1 watt with a ladder-line-fed 270-foot
            >>> dipole at 80 feet up.
            >>>
            >>
            >>
            >>
            >

          • Kai
            Rudy, you are right, JT65 sounds way cooler and more musical than JT9. Joe S, Please read Joe Taylor s documentation for JT9 and for JT65. The occupied
            Message 5 of 12 , Sep 13, 2013
            View Source
            • 0 Attachment
              Rudy,  you are right, JT65 sounds way cooler and more musical than JT9.

              Joe S,
              Please read Joe Taylor's documentation for JT9 and for JT65. The occupied spectrum has
              nothing to do with the noise bandwidth that affects the sensitivity.
              Sensitivity is determined
              by tone duration, coding strength, and decoder algorithm.  Joe Taylor explains it pretty well
              in his documents.  

               I've designed systems with as much 3 GHz occupied bandwidth (UWB systems) that had
              equivalent noise bandwidths of just a few kilohertz. Same is true for CDMA phone technology.

              Joe Taylor's documentation
              states that JT9 threshold sensitivity is -27 dB SNR while
              JT65 is -24 dB SNR both in a reference 2500 Hz BW. So the difference between the two
              is about 3 dB, 2 dB of which is due to tone duration.  Note that there is a "deep search" decoder 
              algorithm that can improve the SNR by another 3 or 4 dB, but that is a decoding algorithm improvement.


              73,
              Kai, KE4PT


              On 9/13/2013 12:37 PM, Rudy Benner wrote:
              The problem with JT9 is that it does not sound so cool as JT65, the almighty cool factor.
               
              r
               
              Sent: Friday, September 13, 2013 12:30 PM
              Subject: Re: [wsjtgroup] An observed Sig-Rep I made btw JT65 & JT9
               
               


              While 2dB applies to the tone duration, the over all bandwidth
              difference between a JT65A signal and a JT9-1 signal is more than
              10 to 1 (~175 Hz vs. ~16 Hz). That would imply a greater high
              bound on the difference in sensitivity - somewhere in the 11 dB
              range.

              I'm sure the real difference is somewhere between 2 dB (individual
              tone bandwidth) and 11 dB (occupied spectrum) ... 4 to 6 dB seems
              to be consistent with observed differences on HF paths.

              73,

              ... Joe, W4TV

              On 9/13/2013 11:39 AM, Kai wrote:
              > Correction ... "JT9 tones are just 0.58 seconds in duration"
              >
              > Additionally Joe Taylor states that JT9 threshold sensitivity is -27 dB
              > SNR, while JT65 is -24 dN SNR both in reference 2500 Hz BW.
              > -Kai, KE4PT
              >
              > On 9/13/2013 11:04 AM, Kai wrote:
              >>
              >>
              >> Hi Bob,
              >> I took a peek at Joe Taylor's WSJT user's guide. JT9 tones are just
              >> 0.58 Hz in duration, so the noise bandwidth is 1/0.58 = 1.7 Hz BW.
              >> JT65 tones are 0.372 s in duration so the noise bandwidth is 2.7 Hz.
              >> So just on the basis of noise bandwidth JT9 would operate at
              >> 20log(2.7/1.7) = 2 dB better S/N ratio. All straight out of Joe
              >> Taylor's documentation.
              >> Improvements in the decoding software increase that even more.
              >>
              >> I think that your observations are valuable confirmation of the
              >> improved S/N performance of JT9 relative to JT65.
              >>
              >> 73
              >> Kai, KE4PT
              >>
              >> On 9/13/2013 8:26 AM, KD7YZ Bob wrote:
              >>> Hey WSJT Group:
              >>>
              >>> Just an FYI (or FWIW) I just noted.
              >>>
              >>> On the morning 30m path to VK3AMA, I saw a report of -18 when I was
              >>> on JT65.
              >>> 4m later I see a report of -14 when I'd just switched to JT9.
              >>>
              >>> My impressions were that JT9, for me, was more sensitive. Obviously this
              >>> is not even close to a scientific experiment, however.
              >>>
              >>> Still though, pretty neat on 1 watt with a ladder-line-fed 270-foot
              >>> dipole at 80 feet up.
              >>>
              >>
              >>
              >>
              >

            • Joe Taylor
              On the relative sensitivities of JT9 and JT65: JT65 and JT9 both use MFSK (multi-tone frequency shift keying). Both modes use one tone (the lowest one) for
              Message 6 of 12 , Sep 13, 2013
              View Source
              • 0 Attachment
                On the relative sensitivities of JT9 and JT65:

                JT65 and JT9 both use MFSK (multi-tone frequency shift keying).

                Both modes use one tone (the lowest one) for time and frequency
                synchronization: JT65 for 63/126 = 50% of the symbols (tone intervals),
                JT9 for 16/85 = 18.8% of the symbols.

                All remaining symbols are used to carry message information. If other
                things were equal, this would give JT9 an advantage of
                10*log10(81.2/50)=2.1 dB.

                Other things aren't equal, though. 64-FSK modulation (as used for the
                information symbols in JT65) is more efficient than the 8-FSK modulation
                used for information symbols in JT9. JT65 uses a Reed Solomon code with
                rate 12/63; JT9 uses a long-constraint convolutional code with K=32,
                rate=1/2, and a zero tail. Both decoders use soft decisions, but the
                algorithms are entirely different. Both codes are "strong", which means
                that false decodes are extremely rare.

                Tests with thousands of simulated transmissions over an AWGN (additive
                white gaussian noise) channel show that JT9 had an advantage of 1-2 dB
                over JT65. For example: on the AWGN channel JT9 decodes correctly 33%
                of the time at S/N = -26 dB; JT65 decodes correctly 14% of the time at
                -25 dB, 70% of the time at -24 dB.

                Real-world situations involve QSB and other propagation-induced effects
                that can affect the probability of correct decodes, even for signals
                with the same average S/N. The low-rate JT65 code brings some advantage
                in the presence of deep QSB, and the wider tone spacing of JT65 offers
                slightly greater immunity to Doppler spread, for example that seen on
                some trans-auroral paths.

                Another thing to keep in mind, if you care about such details: every
                value of S/N reported by the decoders necessarily has an associated
                measurement uncertainty. In the best circumstances (well separated
                signals, no QRM or QRN, flat receiver passband, etc.) the "one-sigma"
                uncertainty is around 1 dB. In many other circumstances the uncertainty
                is larger. JT65 was designed for EME, where true S/N values are never
                greater than 0 (as usual, in a 2500 Hz reference bandwidth). At HF,
                signals are sometimes much stronger. JT65 reports never get bigger than
                -1 dB, no matter how strong a signal may be. JT9 is OK (and reasonably
                linear, in good circumstances) up to +49 dB.

                The bottom line is that the two modes have comparable sensitivity.
                Under benign propagation conditions JT9 has a small (1-2 dB) advantage
                over JT65, and of course it uses less than 1/10 the bandwidth.

                To be sure, JT65 sounds "way cool" but JT9 does not. The reason is that
                the effective Q of filters in your ear is not high enough for you to
                distinguish the JT9 tones from one another. Software filters in the JT9
                decoder have Q around 6000. JT9 sounds "way cool" to the computer.

                -- 73, Joe, K1JT
              • Laurie, VK3AMA
                Reception of your 1watt sig was helped by the 30M 3 element yagi beaming SP NA used here. de Laurie VK3AMA
                Message 7 of 12 , Sep 13, 2013
                View Source
                • 0 Attachment
                  Reception of your 1watt sig was helped by the 30M 3 element yagi beaming
                  SP NA used here.

                  de Laurie VK3AMA

                  On 13/09/2013 10:26 PM, KD7YZ Bob wrote:
                  > Just an FYI (or FWIW) I just noted.
                  >
                  > On the morning 30m path to VK3AMA, I saw a report of -18 when I was on JT65.
                  > 4m later I see a report of -14 when I'd just switched to JT9.
                  >
                  > My impressions were that JT9, for me, was more sensitive. Obviously this
                  > is not even close to a scientific experiment, however.
                  >
                  > Still though, pretty neat on 1 watt with a ladder-line-fed 270-foot
                  > dipole at 80 feet up.
                • Brian Duffell
                  ... I recently changed my rig. The new one seems to drift a few cycles with heat over a 46/50 sec transmission by about 3 hz (at 10MHz, other bands pro
                  Message 8 of 12 , Sep 13, 2013
                  View Source
                  • 0 Attachment
                    Joe Taylor <joe@...> wrote:

                    > The bottom line is that the two modes have comparable sensitivity. Under
                    > benign propagation conditions JT9 has a small (1-2 dB) advantage over
                    > JT65, and of course it uses less than 1/10 the bandwidth.

                    I recently changed my rig. The new one seems to drift a few cycles with heat
                    over a 46/50 sec transmission by about 3 hz (at 10MHz, other bands pro
                    rata)whereas the old one didn't.

                    Decodes in JT65 seem unaffected but JT9 seems to suffer particularly on the
                    higher HF bands. Is this due to a lower immmunity to frequency drift for
                    JT9?

                    --
                    Brian Duffell
                    G3VGZ
                  • Joe Taylor
                    Hi Brian, JT65A uses detection bandwidths 2.69 Hz, and JT9 uses 1.73 Hz. So yes, JT9 will have somewhat greater difficulty with frequency drift. The decoders
                    Message 9 of 12 , Sep 13, 2013
                    View Source
                    • 0 Attachment
                      Hi Brian,

                      JT65A uses detection bandwidths 2.69 Hz, and JT9 uses 1.73 Hz. So yes,
                      JT9 will have somewhat greater difficulty with frequency drift.

                      The decoders for both JT65 and JT9 include "AFC" algorithms that try to
                      detect and remove moderate amounts of frequency drift. The AFC routine
                      in JT65 has been tested and optimized more thoroughly, and because of
                      the greater fraction of signal energy put into the Sync tone, it
                      probably works better. It may be possible to improve JT9's handling of
                      drifting signals, somewhat.

                      -- Joe, K1JT

                      On 9/13/2013 6:39 PM, Brian Duffell wrote:
                      > Joe Taylor<joe@...> wrote:
                      >
                      >> The bottom line is that the two modes have comparable sensitivity. Under
                      >> benign propagation conditions JT9 has a small (1-2 dB) advantage over
                      >> JT65, and of course it uses less than 1/10 the bandwidth.
                      >
                      > I recently changed my rig. The new one seems to drift a few cycles with heat
                      > over a 46/50 sec transmission by about 3 hz (at 10MHz, other bands pro
                      > rata)whereas the old one didn't.
                      >
                      > Decodes in JT65 seem unaffected but JT9 seems to suffer particularly on the
                      > higher HF bands. Is this due to a lower immmunity to frequency drift for
                      > JT9?
                      >
                    • Thomas F Giella W4HM
                      I have had 5 pre-arranged DX QSO s on 15 meters using JT9 followed immediately by JT65A. Power output was always 1 watt to a 288 ft long horizontal loop up at
                      Message 10 of 12 , Sep 14, 2013
                      View Source
                      • 0 Attachment
                        I have had 5 pre-arranged DX QSO's on 15 meters using JT9 followed
                        immediately by JT65A. Power output was always 1 watt to a 288 ft long
                        horizontal loop up at 35 feet. Rig was an Icom IC-7600. At these times radio
                        wave propagation was pretty stable.

                        On every QSO JT9 beat JT65A by approximately 3 db. There were instances
                        where the JT9 signal got through but the JT65A signal did not.

                        73 & GUD DX,
                        Thomas F. Giella W4HM
                        Lakeland, FL, USA
                        w4hm@...

                        BARTG #8531
                        PODXS 070 #349
                        FELD HELD #141
                        30MDG # 691
                        DMC #1243
                        WARC-CC #20

                        W4HM Amateur Radio & SWL Autobiography: http://www.w4hm.org
                      Your message has been successfully submitted and would be delivered to recipients shortly.