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Congratulations on first Transatlantic propagation by ISS reflection

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  • jeff millar
    ISS was precise midway between VC1T and UK at the time of the contact and the visibility circle encompassed both ends. Screen shot from http://satflair.com
    Message 1 of 20 , Jul 8, 2014
    ISS was precise midway between VC1T and UK at the time of the contact and the visibility circle encompassed both ends.

    Screen shot from http://satflair.com

    What's the chance that is a coincidence?

    jeff, wa1hco

    ISS at contact time
  • aflowers@frontiernet.net
    Hi Jeff, The RCS of the ISS is huge, and someone who isn t so burned out from a day s work can run the bistatic radar equation using the effective apertures of
    Message 2 of 20 , Jul 8, 2014
    Hi Jeff,

    The RCS of the ISS is huge, and someone who isn't so burned out from a day's work can run the bistatic radar equation using the effective apertures of the two stations at 144 MHz to see what kind of power shows up at the receiver.  I found a reference that says the ISS as an RCS of 402m^2 (!), but for all I know it might even be big enough for specular reflections at 144Mhz.

    Hams have used the ISS as a passive reflector on 1296 with enough signal margin for SSB and what I think were 10m^2 dishes, so it's probably within the realm of possibility for large QRO stations on 144 MHz.  Makes one think of using longer integration--e.g., JT65 with the necessary doppler correction built in....

    If you're times are right, I think there is every reason to think this was ISS-bounce.  Maybe they will test this theory?

    Andy K0SM/2





    On Tuesday, July 8, 2014 8:13 PM, "jeff millar wa1hco@... [wsjtgroup]" <wsjtgroup-noreply@yahoogroups.com> wrote:


     
    [Attachment(s) from jeff millar included below]
    ISS was precise midway between VC1T and UK at the time of the contact and the visibility circle encompassed both ends.

    Screen shot from http://satflair.com

    What's the chance that is a coincidence?

    jeff, wa1hco

    ISS at contact time


  • rupertdetonquedec
    If it was a reflection off the ISS, the doppler shift would be massive. I ve tried watching it through binos - it doesn t half shift! Was this observed? On the
    Message 3 of 20 , Jul 9, 2014
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      If it was a reflection off the ISS, the doppler shift would be massive.
      I've tried watching it through binos - it doesn't half shift!
      Was this observed?
      On the screen shot, a dF of -193hz is shown, but this probably just means the too stations were not netted spot-on.
      I doubt that JT65A could handle that doppler Andy, but FSK should.

      John
      GW4MBN
    • Roger Rehr
      Great pickup, Jeff! Unfortunately, if the prop mode was reflection off of the ISS, then the reception would not qualify for any of the Brendan Awards, as most
      Message 4 of 20 , Jul 9, 2014
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        Great pickup, Jeff!

        Unfortunately, if the prop mode was reflection off of the ISS, then the reception would not qualify for any of the Brendan Awards, as most folks probably know. 

        For those that weren't aware of that, the IRTS webpage states,
        "Thus man-made reflectors (aircraft, satellites, etc.) as well as EME are excluded".
        http://www.irts.ie/cgi/brendan.cgi , item 6.

        Its still a nice feat, just not eligible for any of the Brendan awards if that is the mechanism.

        73,

        Roger Rehr
        W3SZ


        On Wed, Jul 9, 2014 at 1:12 PM, 'aflowers@...' aflowers@... [wsjtgroup] <wsjtgroup-noreply@yahoogroups.com> wrote:
         
        [Attachment(s) from aflowers@... included below]

        Hi Jeff,

        The RCS of the ISS is huge, and someone who isn't so burned out from a day's work can run the bistatic radar equation using the effective apertures of the two stations at 144 MHz to see what kind of power shows up at the receiver.  I found a reference that says the ISS as an RCS of 402m^2 (!), but for all I know it might even be big enough for specular reflections at 144Mhz.

        Hams have used the ISS as a passive reflector on 1296 with enough signal margin for SSB and what I think were 10m^2 dishes, so it's probably within the realm of possibility for large QRO stations on 144 MHz.  Makes one think of using longer integration--e.g., JT65 with the necessary doppler correction built in....

        If you're times are right, I think there is every reason to think this was ISS-bounce.  Maybe they will test this theory?

        Andy K0SM/2





        On Tuesday, July 8, 2014 8:13 PM, "jeff millar wa1hco@... [wsjtgroup]" <wsjtgroup-noreply@yahoogroups.com> wrote:


         
        [Attachment(s) from jeff millar included below]
        ISS was precise midway between VC1T and UK at the time of the contact and the visibility circle encompassed both ends.

        Screen shot from http://satflair.com

        What's the chance that is a coincidence?

        jeff, wa1hco

        ISS at contact time



      • jeff millar
        Hi John... The issue of Doppler occurred to me as well. If the moving object is directly between the two stations, the Doppler cancels. There a massive
        Message 5 of 20 , Jul 9, 2014
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          Hi John...

          The issue of Doppler occurred to me as well.  If the moving object is directly between the two stations, the Doppler cancels. There a massive Doppler for the signal seen at the ISS, and then the opposite Doppler when that signal reflects on to the receiving station. 

          jeff, wa1hco

          On 07/09/2014 04:31 AM, tonquedec@... [wsjtgroup] wrote:
           

          If it was a reflection off the ISS, the doppler shift would be massive.
          I've tried watching it through binos - it doesn't half shift!
          Was this observed?
          On the screen shot, a dF of -193hz is shown, but this probably just means the too stations were not netted spot-on.
          I doubt that JT65A could handle that doppler Andy, but FSK should.

          John
          GW4MBN


        • aflowers@frontiernet.net
          John, The Doppler shift will be essentially zero at the midpoint of the path, and relatively constant frequenecy if the object is travelling on the
          Message 6 of 20 , Jul 9, 2014
          John,

          The Doppler shift will be essentially zero at the midpoint of the path, and relatively constant frequenecy if the object is travelling on the great-circle path between the stations.  Forward-scatter paths should have relatively little Doppler shift since the relative velocity of the object relative to the two stations cancels out (the ISS moves away from from station A at the velocity as it is moving toward station B.  With something like JT65 you'd have to correct the transform to account for change in Doppler shift, as the relative velocities will change some in practice--the satellite is not moving exactly in a straight line between the two stations, so there will be some change in the observed frequency over time.  But it is possible to estimate that ahead of time if you know the location of the other station, and I suppose you could correct the transform to account for it.  Exercise left to the reader, I suppose  :-)

          EME has the same problem, just less extreme because the overall path length changes more slowly relative to a fast-moving LEO.

          DJ5AR has some history on hams using the ISS and other satellites as a passive reflector.  It looks like VK3-ZL3 has been done on 2m.  Pretty neat stuff, and there are some recordings on the page:

          http://www.dj5ar.de/?page_id=981

          For the curious, one can sort NORAD's catalog by RCS and then put in Decay=0 to have a sorted list of satellites by cross section that are still in orbit:

          http://satellitedebris.net/Database/index.php#

          The ISS dominates the list of things that haven't reentered, but there are many other objects that should be about about 10dB below the ISS.  The radar equation says that power in the receiver is proportional to the radar cross section, and DJ5AR's website mentions using satellites besides the ISS.  There is likely plenty of signal margin for these too, but understand that the radar equation gives you peak power--the orientation of an orbiting object changes, so if may be that only the signal peaks are observable.  

          This makes me question the mechanism behind some of the "impossibly long" supposed MS and ionoscatter contacts that have historically occurred on VHF...the NORAD site will show some things that were several dB bigger than the ISS that have since burned up.  

          Cool stuff, to say the least.  Nice find, Jeff!

          Andy K0SM/2





          On Wednesday, July 9, 2014 4:41 AM, "Roger Rehr 73w3sz@... [wsjtgroup]" <wsjtgroup-noreply@yahoogroups.com> wrote:


           
          Great pickup, Jeff!

          Unfortunately, if the prop mode was reflection off of the ISS, then the reception would not qualify for any of the Brendan Awards, as most folks probably know. 

          For those that weren't aware of that, the IRTS webpage states,
          "Thus man-made reflectors (aircraft, satellites, etc.) as well as EME are excluded".
          http://www.irts.ie/cgi/brendan.cgi , item 6.

          Its still a nice feat, just not eligible for any of the Brendan awards if that is the mechanism.

          73,

          Roger Rehr
          W3SZ


          On Wed, Jul 9, 2014 at 1:12 PM, 'aflowers@...' aflowers@... [wsjtgroup] <wsjtgroup-noreply@yahoogroups.com> wrote:
           
          [Attachment(s) from aflowers@... included below]
          Hi Jeff,

          The RCS of the ISS is huge, and someone who isn't so burned out from a day's work can run the bistatic radar equation using the effective apertures of the two stations at 144 MHz to see what kind of power shows up at the receiver.  I found a reference that says the ISS as an RCS of 402m^2 (!), but for all I know it might even be big enough for specular reflections at 144Mhz.

          Hams have used the ISS as a passive reflector on 1296 with enough signal margin for SSB and what I think were 10m^2 dishes, so it's probably within the realm of possibility for large QRO stations on 144 MHz.  Makes one think of using longer integration--e.g., JT65 with the necessary doppler correction built in....

          If you're times are right, I think there is every reason to think this was ISS-bounce.  Maybe they will test this theory?

          Andy K0SM/2





          On Tuesday, July 8, 2014 8:13 PM, "jeff millar wa1hco@... [wsjtgroup]" <wsjtgroup-noreply@yahoogroups.com> wrote:


           
          [Attachment(s) from jeff millar included below]
          ISS was precise midway between VC1T and UK at the time of the contact and the visibility circle encompassed both ends.

          Screen shot from http://satflair.com

          What's the chance that is a coincidence?

          jeff, wa1hco

          ISS at contact time





        • Joe Taylor
          Hi Jeff, Andy, and all, Of course it s reasonable to explore possible propagation mechanisms for the VC1T-to-G4SWX path. Please consider the following: 1. As
          Message 7 of 20 , Jul 9, 2014
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            Hi Jeff, Andy, and all,

            Of course it's reasonable to explore possible propagation mechanisms for
            the VC1T-to-G4SWX path. Please consider the following:

            1. As I understand it, and from the published screen shot, the signal
            received at G4SWX had all the characteristics of a short meteor ping of
            about 150 ms duration.

            2. Those who have made "ISS-bounce" QSOs have found the signals last for
            several *minutes*. Plenty of time for lengthy CW exchanges at normal
            (15-20 wpm) speeds.

            3. The time of reception is accurately known, so it's possible to
            calculate accurately the Doppler shift on the VC1T --> ISS --> G4SWX
            path. Perhaps the correct answer is something no more than a few
            hundred Hz, but we don't yet know this. The calculation has not been done.

            Occam's razor states that among competing hypotheses, the one with the
            fewest assumptions should be selected.

            At present then, by a wide margin, it seems to me that the simplest
            explanation of the signal received by G4SWX is reflection from a meteor
            trail aided by either tropospheric or E-layer refraction.

            -- 73, Joe, K1JT
          • Jeff Moore
            How does the doppler shift cancel? Both the transmitting site and receiving site need to be shfted from the center frequency in order for the signal to get
            Message 8 of 20 , Jul 9, 2014
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              How does the doppler shift cancel?  Both the transmitting site and receiving site need to be shfted from the center frequency in order for the signal to get through.  How is that cancelled in any way??  Especially with the object on a path between the 2 sites??

              Jeff Moore  --  KE7ACY

              On Wed, Jul 9, 2014 at 4:38 AM, jeff millar wa1hco@... [wsjtgroup] <wsjtgroup-noreply@yahoogroups.com> wrote:
               

              Hi John...

              The issue of Doppler occurred to me as well.  If the moving object is directly between the two stations, the Doppler cancels. There a massive Doppler for the signal seen at the ISS, and then the opposite Doppler when that signal reflects on to the receiving station. 

              jeff, wa1hco


              On 07/09/2014 04:31 AM, tonquedec@... [wsjtgroup] wrote:
               

              If it was a reflection off the ISS, the doppler shift would be massive.
              I've tried watching it through binos - it doesn't half shift!
              Was this observed?
              On the screen shot, a dF of -193hz is shown, but this probably just means the too stations were not netted spot-on.
              I doubt that JT65A could handle that doppler Andy, but FSK should.

              John
              GW4MBN



            • Joe Taylor
              Hi Jeff, Doppler shift depends on the time derivative (rate of change) of the full path length, Transmitter-- Reflector-- Receiver. This derivative is
              Message 9 of 20 , Jul 9, 2014
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                Hi Jeff,

                Doppler shift depends on the time derivative (rate of change) of the
                full path length, Transmitter-->Reflector-->Receiver. This derivative
                is necessarily close to zero when the reflector is close to the
                midpoint, unless the reflector's velocity has a significant "vertical"
                component.

                -- Joe, K1JT

                KE7ACY wrote:
                > How does the doppler shift cancel? Both the transmitting site and
                > receiving site need to be shfted from the center frequency in order for the
                > signal to get through. How is that cancelled in any way?? Especially with
                > the object on a path between the 2 sites??
                >
                > Jeff Moore -- KE7ACY
                >
                > On Wed, Jul 9, 2014 at 4:38 AM, jeff millar wa1hco@... [wsjtgroup]<
                > wsjtgroup-noreply@yahoogroups.com> wrote:
                >
                >>
                >>
                >> Hi John...
                >>
                >> The issue of Doppler occurred to me as well. If the moving object is
                >> directly between the two stations, the Doppler cancels. There a massive
                >> Doppler for the signal seen at the ISS, and then the opposite Doppler when
                >> that signal reflects on to the receiving station.
                >>
                >> jeff, wa1hco
                >>
                >>
                >> On 07/09/2014 04:31 AM, tonquedec@... [wsjtgroup] wrote:
                >>
                >>
                >>
                >> If it was a reflection off the ISS, the doppler shift would be massive.
                >> I've tried watching it through binos - it doesn't half shift!
                >> Was this observed?
                >> On the screen shot, a dF of -193hz is shown, but this probably just means
                >> the too stations were not netted spot-on.
                >> I doubt that JT65A could handle that doppler Andy, but FSK should.
                >>
                >> John
                >> GW4MBN
                >>
                >>
                >>
                >
              • rupertdetonquedec
                My understanding is that there is a doppler shift, but neither station notices? Eg: Assuming 100Hz shift: VE station transmits on 144.155 G station receives
                Message 10 of 20 , Jul 9, 2014
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                  My understanding is that there is a doppler shift, but neither station notices?

                  Eg: Assuming 100Hz shift:

                  VE station transmits on 144.155
                  G station receives him on 144.156 due to +100Hz doppler shift (ISS moving towards him)
                  So - G station transmits on 144.156
                  VE station receives him on 144.155 due to -100Hz doppler shift (ISS moving away from him)

                  So neither station notices. VE thinks the QSO is on 144.155. G thinks the QSO is on 144.156

                  This assumes the ISS is following the exact great circle path between the two stations - which it probably won't be, hence the symmetry will not be perfect, and some drift may be noticed.

                  John
                  GW4MBN
                • aflowers@frontiernet.net
                  Hi Joe, The picture posted on the website appears to be much longer duration than a few 150ms--several seconds in fact, and of the low-in-the-noise variety
                  Message 11 of 20 , Jul 9, 2014
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                    Hi Joe,

                    The picture posted on the website appears to be much longer duration than a few 150ms--several seconds in fact, and of the low-in-the-noise variety (perhaps it was in the noise and the operator clicked around for a manual decode?).  If the signal appears at the beginning of the sequence then the path may have been there for a as much as 30 seconds prior to that.  But I'm just looking at a screen shot, which isn't exactly good data for us to speculate with.  

                    The mutual footprint is not long--probably a couple minutes at best, and within that you probably have antenna patterns, Fresnel zones, Faraday rotation and anything else that might allow a signal to rise out of the noise for a few seconds. DJ5AR and crew were all relatively close together, had long windows, and backscatter paths.  Other than berhaps VK3UM/ZL3AAD, has anyone tried a long FS path at low angles?

                    Anyway, here's the only picture I've seen, which doesn't seem to show the spectrogram of the time period.  For all I know there may be more captures.  It would be interesting to analyze the 30sec prior to the decoded signal to see if anything is there, but the transmitter probably wasn't on.

                    http://www.brendanquest.org/reception-reports.html

                    It's all very easy to be be skeptical from my armchair for what is, regardless, quite an accomplishment.

                    In any event, I came up with around -118dBm peak power in the receiver using KW TX power, 25dBi antennas, sigma = 400m^2, and 2000 KM between ISS and both stations, but someone who knows what they are doing should see what they get.  It seems high to me.  I probably messed up a conversion somewhere.  

                    One way to distinguish the propagation mode would be to empirically prove the signal is stronger than a passive reflector like the ISS could be, but that might mean making power measurements.  It's probably worth figuring out just what man-made objects are large enough, and since we know where they are when it is possible to rule them out.  The thing I'm realizing is that teasing out propagation modes may be a more difficult exercise than it appears!  

                    In the end, the IRTS gets to apply Bayes' rule for their awards, not us.  It would be really interesting to see if any EME stations in the beyond-E-layer range want to try forward scatter of the ISS to get some measurements of signal strength over time.  Alas, I'm not in a position to do that...

                    This is all very interesting, to say the least.

                    Andy K0SM/2




                    On Wednesday, July 9, 2014 12:25 PM, "Jeff Moore tnetcenter@... [wsjtgroup]" <wsjtgroup-noreply@yahoogroups.com> wrote:


                     
                    How does the doppler shift cancel?  Both the transmitting site and receiving site need to be shfted from the center frequency in order for the signal to get through.  How is that cancelled in any way??  Especially with the object on a path between the 2 sites??

                    Jeff Moore  --  KE7ACY

                    On Wed, Jul 9, 2014 at 4:38 AM, jeff millar wa1hco@... [wsjtgroup] <wsjtgroup-noreply@yahoogroups.com> wrote:
                     
                    Hi John...

                    The issue of Doppler occurred to me as well.  If the moving object is directly between the two stations, the Doppler cancels. There a massive Doppler for the signal seen at the ISS, and then the opposite Doppler when that signal reflects on to the receiving station. 

                    jeff, wa1hco


                    On 07/09/2014 04:31 AM, tonquedec@... [wsjtgroup] wrote:
                     
                    If it was a reflection off the ISS, the doppler shift would be massive.
                    I've tried watching it through binos - it doesn't half shift!
                    Was this observed?
                    On the screen shot, a dF of -193hz is shown, but this probably just means the too stations were not netted spot-on.
                    I doubt that JT65A could handle that doppler Andy, but FSK should.

                    John
                    GW4MBN




                  • Joe Taylor
                    Hi John, No, your description is not correct. If you choose to analyze each leg separately, you can say that an upward frequency shift between station A and
                    Message 12 of 20 , Jul 9, 2014
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                      Hi John,

                      No, your description is not correct.

                      If you choose to analyze each leg separately, you can say that an upward
                      frequency shift between station A and the reflector is canceled by a
                      nearly equal downward shift of the reflected signal on its way to station B.

                      Or you can treat both path legs together. What matters is the rate at
                      which the total path length is changing. With the reflector near the
                      path midpoint, that rate will be close to zero unless the reflector's
                      velocity has a significant vertical component.

                      -- Joe, K1JT

                      On 7/9/2014 1:59 PM, tonquedec@... [wsjtgroup] wrote:
                      > My understanding is that there is a doppler shift, but neither station notices?
                      >
                      > Eg: Assuming 100Hz shift:
                      >
                      > VE station transmits on 144.155
                      > G station receives him on 144.156 due to +100Hz doppler shift (ISS moving towards him)
                      > So - G station transmits on 144.156
                      > VE station receives him on 144.155 due to -100Hz doppler shift (ISS moving away from him)
                      >
                      > So neither station notices. VE thinks the QSO is on 144.155. G thinks the QSO is on 144.156
                      >
                      > This assumes the ISS is following the exact great circle path between the two stations - which it probably won't be, hence the symmetry will not be perfect, and some drift may be noticed.
                      >
                      > John
                      > GW4MBN
                    • Joe Taylor
                      Hi Andy, To be sure, the full duration of the VC1T signal received at G4SWX was as much as three or four seconds. The number I mentioned, 150 ms, corresponds
                      Message 13 of 20 , Jul 9, 2014
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                        Hi Andy,

                        To be sure, the full duration of the VC1T signal received at G4SWX was
                        as much as three or four seconds. The number I mentioned, 150 ms,
                        corresponds only to the nearly unbroken string of 22 correctly decoded
                        characters, "C1T CQ VC T CQ VC1T CQ" on the final line on the screen
                        shot. Another dozen or more recognizable characters are present in the
                        two preceding lines. As you know, this is just the sort of behavior one
                        often sees with moderately strong (somewhere between "under-dense" and
                        "over-dense"?) reflections from meteor trails, on 2 meters.

                        Alas, John (G4SWX) had not engaged WSJT's "Save All" option when these
                        signals were received. So there is no recording. But one assumes that
                        John was listening, and paying attention. Anyone who has used FSK441
                        for meteor scatter knows what those signals sound like, and it's certain
                        that John has that experience. I have very little doubt that the sound
                        of FSK441 signals reflected by ISS would be rather different. In
                        particular, amplitude changes would be much slower.

                        We will surely learn more, in due course. The report on the "Brendan
                        Quest" web site mentions additional reception of "partials" from
                        station(s?) in Ireland.

                        -- Joe, K1JT

                        On 7/9/2014 2:07 PM, 'aflowers@...' aflowers@...
                        [wsjtgroup] wrote:
                        > Hi Joe,
                        >
                        > The picture posted on the website appears to be much longer duration than a few 150ms--several seconds in fact, and of the low-in-the-noise variety (perhaps it was in the noise and the operator clicked around for a manual decode?). If the signal appears at the beginning of the sequence then the path may have been there for a as much as 30 seconds prior to that. But I'm just looking at a screen shot, which isn't exactly good data for us to speculate with.
                        >
                        > The mutual footprint is not long--probably a couple minutes at best, and within that you probably have antenna patterns, Fresnel zones, Faraday rotation and anything else that might allow a signal to rise out of the noise for a few seconds. DJ5AR and crew were all relatively close together, had long windows, and backscatter paths. Other than berhaps VK3UM/ZL3AAD, has anyone tried a long FS path at low angles?
                        >
                        > Anyway, here's the only picture I've seen, which doesn't seem to show the spectrogram of the time period. For all I know there may be more captures. It would be interesting to analyze the 30sec prior to the decoded signal to see if anything is there, but the transmitter probably wasn't on.
                        >
                        > http://www.brendanquest.org/reception-reports.html
                        >
                        > It's all very easy to be be skeptical from my armchair for what is, regardless, quite an accomplishment.
                        >
                        > In any event, I came up with around -118dBm peak power in the receiver using KW TX power, 25dBi antennas, sigma = 400m^2, and 2000 KM between ISS and both stations, but someone who knows what they are doing should see what they get. It seems high to me. I probably messed up a conversion somewhere.
                        >
                        > One way to distinguish the propagation mode would be to empirically prove the signal is stronger than a passive reflector like the ISS could be, but that might mean making power measurements. It's probably worth figuring out just what man-made objects are large enough, and since we know where they are when it is possible to rule them out. The thing I'm realizing is that teasing out propagation modes may be a more difficult exercise than it appears!
                        >
                        >
                        > In the end, the IRTS gets to apply Bayes' rule for their awards, not us. It would be really interesting to see if any EME stations in the beyond-E-layer range want to try forward scatter of the ISS to get some measurements of signal strength over time. Alas, I'm not in a position to do that...
                        >
                        > This is all very interesting, to say the least.
                        >
                        > Andy K0SM/2
                        >
                        >
                        >
                        >
                        > On Wednesday, July 9, 2014 12:25 PM, "Jeff Moore tnetcenter@... [wsjtgroup]"<wsjtgroup-noreply@yahoogroups.com> wrote:
                        >
                        >
                        >
                        >
                        > How does the doppler shift cancel? Both the transmitting site and receiving site need to be shfted from the center frequency in order for the signal to get through. How is that cancelled in any way?? Especially with the object on a path between the 2 sites??
                        >
                        >
                        >
                        > Jeff Moore -- KE7ACY
                        >
                        >
                        >
                        > On Wed, Jul 9, 2014 at 4:38 AM, jeff millar wa1hco@... [wsjtgroup]<wsjtgroup-noreply@yahoogroups.com> wrote:
                        >
                        >
                        >>
                        >> Hi John...
                        >>
                        >> The issue of Doppler occurred to me as well. If the moving object
                        > is directly between the two stations, the Doppler cancels. There a
                        > massive Doppler for the signal seen at the ISS, and then the
                        > opposite Doppler when that signal reflects on to the receiving
                        > station.
                        >>
                        >> jeff, wa1hco
                        >>
                        >>
                        >> On 07/09/2014 04:31 AM, tonquedec@... [wsjtgroup] wrote:
                        >>
                        >>
                        >>> If it was a reflection off the ISS, the doppler shift would be massive.
                        >>> I've tried watching it through binos - it doesn't half
                        > shift!
                        >>> Was this observed?
                        >>> On the screen shot, a dF of -193hz is shown, but this
                        > probably just means the too stations were not netted
                        > spot-on.
                        >>> I doubt that JT65A could handle that doppler Andy, but FSK
                        > should.
                        >>>
                        >>> John
                        >>> GW4MBN
                        >>
                        >
                        >
                      • rupertdetonquedec
                        Thanks Joe for the clarification. John GW4MBN
                        Message 14 of 20 , Jul 9, 2014
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                          Thanks Joe for the clarification.

                          John
                          GW4MBN
                        • Sebastian, W4AS
                          VC1T said at 20:01 UTC today: ôwe have reports of partials possibly another complete decodeàitÆs not available to us yetö. Their Internet connection has
                          Message 15 of 20 , Jul 9, 2014
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                            VC1T said at 20:01 UTC today: “we have reports of partials possibly another complete decode…it’s not available to us yet”.

                            Their Internet connection has not always been reliable, and they are concentrating their efforts to on-the-air activities.

                            73 de Sebastian, W4AS



                            On Jul 09, 2014, at 3:35 PM, Joe Taylor joe@... [wsjtgroup] <wsjtgroup-noreply@yahoogroups.com> wrote:

                            > We will surely learn more, in due course. The report on the "Brendan
                            > Quest" web site mentions additional reception of "partials" from
                            > station(s?) in Ireland.
                            >
                            > -- Joe, K1JT
                          • tony everhardt
                            Wondering if FSK441 would make any difference. Of course I realize that the Doppler shift would still be the same, But the data info is much faster. N8WAC On
                            Message 16 of 20 , Jul 9, 2014
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                              Wondering if FSK441 would make any difference. Of course I realize that the Doppler shift would still be the same, But the data info is much faster.

                              N8WAC


                              On Wednesday, July 9, 2014 7:49 AM, "'aflowers@...' aflowers@... [wsjtgroup]" <wsjtgroup-noreply@yahoogroups.com> wrote:


                               
                              [Attachment(s) from aflowers@... included below]
                              John,

                              The Doppler shift will be essentially zero at the midpoint of the path, and relatively constant frequenecy if the object is travelling on the great-circle path between the stations.  Forward-scatter paths should have relatively little Doppler shift since the relative velocity of the object relative to the two stations cancels out (the ISS moves away from from station A at the velocity as it is moving toward station B.  With something like JT65 you'd have to correct the transform to account for change in Doppler shift, as the relative velocities will change some in practice--the satellite is not moving exactly in a straight line between the two stations, so there will be some change in the observed frequency over time.  But it is possible to estimate that ahead of time if you know the location of the other station, and I suppose you could correct the transform to account for it.  Exercise left to the reader, I suppose  :-)

                              EME has the same problem, just less extreme because the overall path length changes more slowly relative to a fast-moving LEO.

                              DJ5AR has some history on hams using the ISS and other satellites as a passive reflector.  It looks like VK3-ZL3 has been done on 2m.  Pretty neat stuff, and there are some recordings on the page:

                              http://www.dj5ar.de/?page_id=981

                              For the curious, one can sort NORAD's catalog by RCS and then put in Decay=0 to have a sorted list of satellites by cross section that are still in orbit:

                              http://satellitedebris.net/Database/index.php#

                              The ISS dominates the list of things that haven't reentered, but there are many other objects that should be about about 10dB below the ISS.  The radar equation says that power in the receiver is proportional to the radar cross section, and DJ5AR's website mentions using satellites besides the ISS.  There is likely plenty of signal margin for these too, but understand that the radar equation gives you peak power--the orientation of an orbiting object changes, so if may be that only the signal peaks are observable.  

                              This makes me question the mechanism behind some of the "impossibly long" supposed MS and ionoscatter contacts that have historically occurred on VHF...the NORAD site will show some things that were several dB bigger than the ISS that have since burned up.  

                              Cool stuff, to say the least.  Nice find, Jeff!

                              Andy K0SM/2





                              On Wednesday, July 9, 2014 4:41 AM, "Roger Rehr 73w3sz@... [wsjtgroup]" <wsjtgroup-noreply@yahoogroups.com> wrote:


                               
                              Great pickup, Jeff!

                              Unfortunately, if the prop mode was reflection off of the ISS, then the reception would not qualify for any of the Brendan Awards, as most folks probably know. 

                              For those that weren't aware of that, the IRTS webpage states,
                              "Thus man-made reflectors (aircraft, satellites, etc.) as well as EME are excluded".
                              http://www.irts.ie/cgi/brendan.cgi , item 6.

                              Its still a nice feat, just not eligible for any of the Brendan awards if that is the mechanism.

                              73,

                              Roger Rehr
                              W3SZ


                              On Wed, Jul 9, 2014 at 1:12 PM, 'aflowers@...' aflowers@... [wsjtgroup] <wsjtgroup-noreply@yahoogroups.com> wrote:
                               
                              [Attachment(s) from aflowers@... included below]
                              Hi Jeff,

                              The RCS of the ISS is huge, and someone who isn't so burned out from a day's work can run the bistatic radar equation using the effective apertures of the two stations at 144 MHz to see what kind of power shows up at the receiver.  I found a reference that says the ISS as an RCS of 402m^2 (!), but for all I know it might even be big enough for specular reflections at 144Mhz.

                              Hams have used the ISS as a passive reflector on 1296 with enough signal margin for SSB and what I think were 10m^2 dishes, so it's probably within the realm of possibility for large QRO stations on 144 MHz.  Makes one think of using longer integration--e.g., JT65 with the necessary doppler correction built in....

                              If you're times are right, I think there is every reason to think this was ISS-bounce.  Maybe they will test this theory?

                              Andy K0SM/2





                              On Tuesday, July 8, 2014 8:13 PM, "jeff millar wa1hco@... [wsjtgroup]" <wsjtgroup-noreply@yahoogroups.com> wrote:


                               
                              [Attachment(s) from jeff millar included below]
                              ISS was precise midway between VC1T and UK at the time of the contact and the visibility circle encompassed both ends.

                              Screen shot from http://satflair.com/

                              What's the chance that is a coincidence?

                              jeff, wa1hco

                              ISS at contact time







                            • jeff millar
                              Joe, et al... On the issue of probabilities of ISS being in that location... * The satflair.com site shows the ISS camera circle covering VC1T and G4SWX for 89
                              Message 17 of 20 , Jul 9, 2014
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                                Joe, et al...

                                On the issue of probabilities of ISS being in that location...
                                • The satflair.com site shows the ISS camera circle covering VC1T and G4SWX for 89 seconds
                                • That's not the same as RF visibility, but lets use that number
                                • The ISS returns to a location which covers both stations every 22 hours and 50 minutes
                                • That's 89 seconds every 82200 seconds.
                                • For a randomly selected contact time, that's a probability of .001

                                So, rephrasing... there's roughly one chance in 1000 that the ISS just happened to be precisely there when G4SWX received a signal from VC1T.

                                To me, Occam's Razor suggests ISS as the source of the reflection. 

                                The radar cross section of an object with a large complex shape is _very_ irregular with peaks and nulls at narrowly spaced angles.  It seems reasonable that the ISS could exhibit fast changes in effective radar cross section as it's aspect angle to the Tx and Rx stations changes.

                                But, the fading characteristics of the signal do roughly match a meteor with a long duration.  If I was to guess, a meteor in the 99 to 99.8 percentile range. Rare, but not that rare given meteors every minute or two.

                                MS ops have an impression of the characteristics of "large meteors" with long duration.  But do we know they are really meteors?  Satellite reflection may be more common than thought.

                                Here's suggestion for the other active MS people on this list.

                                • Pull up your files of those FSK441 decodes that lasted 5, 10, 20 seconds
                                • Check that time against the location of the ISS or other large Sat's at the same time
                                  •  Andy probably can recommend a good web tool, satflare is not the right one
                                • W2SZ has a 20 sec decode somewhere that will be interesting to look at.
                                  • Dave, do you know where to find that file?

                                jeff, wa1hco


                                On 07/09/2014 09:49 AM, Joe Taylor joe@... [wsjtgroup] wrote:
                                 

                                Hi Jeff, Andy, and all,

                                Of course it's reasonable to explore possible propagation mechanisms for
                                the VC1T-to-G4SWX path. Please consider the following:

                                1. As I understand it, and from the published screen shot, the signal
                                received at G4SWX had all the characteristics of a short meteor ping of
                                about 150 ms duration.

                                2. Those who have made "ISS-bounce" QSOs have found the signals last for
                                several *minutes*. Plenty of time for lengthy CW exchanges at normal
                                (15-20 wpm) speeds.

                                3. The time of reception is accurately known, so it's possible to
                                calculate accurately the Doppler shift on the VC1T --> ISS --> G4SWX
                                path. Perhaps the correct answer is something no more than a few
                                hundred Hz, but we don't yet know this. The calculation has not been done.

                                Occam's razor states that among competing hypotheses, the one with the
                                fewest assumptions should be selected.

                                At present then, by a wide margin, it seems to me that the simplest
                                explanation of the signal received by G4SWX is reflection from a meteor
                                trail aided by either tropospheric or E-layer refraction.

                                -- 73, Joe, K1JT


                              • Joe Taylor
                                Hi Jeff, ... Of course we do. Work with meteor scatter on 2m goes back to the 1950s, well before the modern space age. Meteor pings haven t become much more
                                Message 18 of 20 , Jul 9, 2014
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                                  Hi Jeff,

                                  WA1HCO wrote:

                                  > MS ops have an impression of the characteristics of "large meteors" with
                                  > long duration. But do we know they are really meteors?

                                  Of course we do. Work with meteor scatter on 2m goes back to the 1950s,
                                  well before the modern space age. Meteor pings haven't become much more
                                  frequent, now that many mad-made satellites are in orbit.

                                  Anyone who has made a lot of MS QSOs knows what those signals sound
                                  like... and also knows that the occasional over-dense "blue whizzers,"
                                  with reflections lasting many seconds, are not all that rare.

                                  I should make it clear that I have no horse in this race. Like others
                                  who have contributed here, I'm just a bystander with an interest in
                                  knowing the truth about a reported phenomenon.

                                  -- Joe, K1JT
                                • Jim Kennedy
                                  The screenshot shows a VC1T decode at 13:32:25. At that time, ISS Tracker has the ISS over the eastern US seaboard. With the yagi they were using at VC1T I
                                  Message 19 of 20 , Jul 9, 2014
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                                    The screenshot shows a VC1T decode at 13:32:25. At that time, ISS Tracker has the ISS over the eastern US seaboard. With the yagi they were using at VC1T I find it highly unlikely that the ISS would see enough RF to be reflected across the pond from that location. I am assuming the screenshot is in Zulu time. What am I missing ? Where did that decode come from ?
                                     
                                     
                                    Jim
                                    W7OUU
                                    Sent: Thursday, July 10, 2014 01:49
                                    Subject: Re: [wsjtgroup] Congratulations on first Transatlantic propagation by ISS reflection
                                     
                                     

                                    Hi Jeff,

                                    WA1HCO wrote:

                                    > MS ops have an impression of the
                                    characteristics of "large meteors" with
                                    > long duration. But do we know
                                    they are really meteors?

                                    Of course we do. Work with meteor scatter on 2m goes back to the 1950s,
                                    well before the modern space age. Meteor pings haven't become much more
                                    frequent, now that many mad-made satellites are in orbit.

                                    Anyone who has made a lot of MS QSOs knows what those signals sound
                                    like... and also knows that the occasional over-dense "blue whizzers,"
                                    with reflections lasting many seconds, are not all that rare.

                                    I should make it clear that I have no horse in this race. Like others
                                    who have contributed here, I'm just a bystander with an interest in
                                    knowing the truth about a reported phenomenon.

                                    -- Joe, K1JT

                                  • aflowers@frontiernet.net
                                    Jim, I m guessing that decode is probably a GM station calling on the alternate half minute.  I m not sure what the arrangements are for the transmitters on
                                    Message 20 of 20 , Jul 9, 2014
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                                      Jim,

                                      I'm guessing that decode is probably a GM station calling on the alternate half minute.  I'm not sure what the arrangements are for the transmitters on the EU side...there's sure  to be more to the story, so we'll just have to wait for that.  The good news is they have a few more days, and we all have something new to talk about....and I've already learned something about countermeasures for detecting stealth aircraft.  See where ham radio can take you?  :-)

                                      I ran some numbers with a clearer head and ended up with -144dBm which is more reasonable (4000km total path with ISS in the middle, 700w TX power, 25dBi antenna gain both ends, 400m^2 RCS of the ISS), but I'm really out of my element here.  I'm hoping someone who understands radar can run the numbers. 

                                      This has really fascinated me.  I hope they make a Q one way or another....

                                      Andy K0SM/2





                                      On Wednesday, July 9, 2014 10:03 PM, "'Jim Kennedy' kennedyjp@... [wsjtgroup]" <wsjtgroup-noreply@yahoogroups.com> wrote:


                                       
                                      The screenshot shows a VC1T decode at 13:32:25. At that time, ISS Tracker has the ISS over the eastern US seaboard. With the yagi they were using at VC1T I find it highly unlikely that the ISS would see enough RF to be reflected across the pond from that location. I am assuming the screenshot is in Zulu time. What am I missing ? Where did that decode come from ?
                                       
                                       
                                      Jim
                                      W7OUU
                                      Sent: Thursday, July 10, 2014 01:49
                                      Subject: Re: [wsjtgroup] Congratulations on first Transatlantic propagation by ISS reflection
                                       
                                       
                                      Hi Jeff,

                                      WA1HCO wrote:

                                      > MS ops have an impression of the characteristics of "large meteors" with
                                      > long duration. But do we know they are really meteors?

                                      Of course we do. Work with meteor scatter on 2m goes back to the 1950s,
                                      well before the modern space age. Meteor pings haven't become much more
                                      frequent, now that many mad-made satellites are in orbit.

                                      Anyone who has made a lot of MS QSOs knows what those signals sound
                                      like... and also knows that the occasional over-dense "blue whizzers,"
                                      with reflections lasting many seconds, are not all that rare.

                                      I should make it clear that I have no horse in this race. Like others
                                      who have contributed here, I'm just a bystander with an interest in
                                      knowing the truth about a reported phenomenon.

                                      -- Joe, K1JT


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