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Re: [SpectrumLabUsers] SETI Experiment - Help Needed

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  • M. Ben Schuetz
    Hi Mark, Well, I have had to sort through a whole list of unexpected, mostly local signals over the past several years. Once, I had a really interesting
    Message 1 of 11 , Jul 9, 2013
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      Hi Mark,

      Well, I have had to sort through a whole list of unexpected, mostly local signals over the past several years.  Once, I had a really interesting "signal" that came and went in a strange manner.  After ruling out local electrical noise sources, I thought maybe it was some kind of telescope mechanical resonance.  Tested for that, but no response.  The telescope and electronics were mostly immune to wind gusts and local lighting.  Finally, I found that a very slight gusty breeze cause this type of "signal".  The breeze gust was so light, I hardly noticed it. 
      Some changes in the electronics sorted that out. 

      Best, Ben

      On 7/9/2013 2:39 PM, Mark McCarron wrote:
       

      Ben,

      I'm quite sure the only little green men I am likely to encounter will be of the camouflaged variety.

      Now, it is quite possible that it is something local and reflecting off clouds.  I also need to rule out every element in my receive chain.  So, I am ordering new equipment now and I should have a completely new reference sometime next week.

      Regards,

      Mark McCarron


      To: SpectrumLabUsers@yahoogroups.com
      From: kg4lra@...
      Date: Tue, 9 Jul 2013 09:04:13 -0500
      Subject: Re: [SpectrumLabUsers] SETI Experiment - Help Needed

       

      Hi Mark,

      Here's a couple of things to help in your evaluation. 

      Making the device highly directive is a good way to sort out the source of "the signal".  But a straw or shrink tubing will not do it for IR.  IR goes through thin plastics like grease through a goose.   So, something more substantial, like 1/4" copper tube, etc. would work. 

      Now the bad news.  Laser signals from our neighbors are most likely going to be far too feeble for a phototransistor to detect, even with a large telescope.  For instance, and roughly, the laser power required to present a NIR wavelength 1 ns pulse signal of just 100 photons/m^2 at interstellar distances and with a conic section diameter of 1 astronomical unit, is about 50 terrawatts.   Presented here on earth with such a signal, and with a phototransistor active area of maybe 1e-6 meters, you could collect a whole .0001 photon.  It might be asking a bit much of the little guy.  

      Ben


      On 7/8/2013 11:18 PM, wb6bnq wrote:
       
      Hi Mark,

      You could take a straw and cover it with black shrink tubing and put it over the photodiode.  Then you could aim it around to look for the direction of the source or sources in question.  Just make sure that no light can get into the diode except down the straw.

      Bill....WB6BNQ


      Mark McCarron wrote:
       
      Someone mentioned using a phototransistor to detect SETI signals encoded in light a while back on this mailing list.  I liked the idea and constructed my own setup using an opamp and Near-IR phototransistor.  I've been playing about with it and pushing the output to spectrumlab. 

      I decided to leave it on overnight and build a good picture of noise as a reference.  I used the following settings for the FFT:

      Effect of FFT settings with fs= 48.0000 kHz:
      Width of one FFT-bin: 91.5527 mHz
      Equiv. noise bandwidth: 137.329 mHz
      Max freq range: 0.00000 Hz .. 24.0000 kHz
      FFT window time: 10.923 s
      Overlap from scroll interval: 75.0 %

      I expected a 50Hz hum plus some harmonics, as well as a higher frequency hum from my monitors.  This can be seen in the linked image below as the major peaks.  The interesting thing was that I discovered another source.  This is the series of lines in the image, that periodically get stronger.  This sources begins at 10.52Hz and multiples thereof until 600Hz, then there is a gap and the pattern repeats.

      I found that the source was coming through my window, reflecting off my monitors and striking the detector.  I also found that it passed through curtains and plastic venetian blinds.  Standing in front of the window, did block the signal.  I traced through the circuit looking for noise, replaced capacitors, etc.  I can find no faults and nothing that would generate the pattern.

      http://i.imgur.com/EMsuwgw.jpg

      Checking the output Window, it looks like each of those signals is a sine wave but the phase is changing as well as the amplitude.  I had a look at the 50Hz power signal and the phase changes do not match it, so it is not something connected directly to the local grid.

      Finally, and this is part that is bugging me, the elevation puts the signal source in the sky.  My first instinct was LIDAR, but to maintain this signal accuracy would require a hell of a setup. 

      Does anyone have any suggestions???

      Regards,

      Mark McCarron




    • M. Ben Schuetz
      A few days ago I raised a question about signals with and without harmonics. Since I have only been using SL in one way for the past couple of years, the
      Message 2 of 11 , Jul 9, 2013
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        A few days ago I raised a question about "signals" with and without harmonics.  Since I have only been using SL in one way for the past couple of years, the other signal types weren't that familiar to me.  Graham and Wolf responded with thought provoking observations.  So, I made a few simple tests with a signal generator to explore the issue.

        Here's the situation.  A square wave or any periodic pulsed signals is coupled into the computer audio board through a 0.1 uF cap.  Given the internal resistance of the audio board, this results in roughly 100 us pulses.  SL responds to these showing approximately equal amplitude signals of all the harmonics.  If a pulse or two are missing here and there, the appropriate harmonic is enhanced.  The consequence of this is that any signal not having 2nd, 3rd, . . . harmonic bins are just noise and can be disregarded.  Hopefully, and even better, in software they can be discarded from any further processing.  That would bring the noise baseline down to about nothing while leaving a clean detected signal.
        It would obviate the need to look at waterfall clutter and improve the minimum detectable limits.

        This may have applications anywhere a periodic signal can be converted to pulses before going to SL.

        I suspect the software changes would not be huge.  Or, is there a way to do this external of the SL source code.  Any thoughts?

        Ben

      • Jurgen Bartels
        ... You can write your own plugin, it works very well, I have made a few for my own purposes. Jurgen Bartels Suellwarden, N. Germany Ant. hor: 29-45MHz 7-el,
        Message 3 of 11 , Jul 9, 2013
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          > I suspect the software changes would not be huge. Or, is there a way to
          > do this external of the SL source code. Any thoughts?

          You can write your own plugin, it works very well, I have made a few for my own
          purposes.



          Jurgen Bartels Suellwarden, N. Germany
          Ant. hor: 29-45MHz 7-el, 45-87MHz 11-el, FM 15.11, Band-3:13-el, UHF:48-el
          TV: Winradio G305 / Fly2000 + video noise filter & variable IF BW
          FM: Downconverter + Perseus + Speclab as WFM demod.
          MW: 30 x 4m EWE 320° with JB-terminator, Winradio & Perseus
          http://zeiterfassung.3sdesign.de/station_list.htm
          http://dx.3sdesign.de/tv_offset_list.htm
        • M. Ben Schuetz
          Thanks Jurgen. I ll look over your work and probably get back to you with questions. Best - Ben ... Thanks Jurgen. I ll look over your work and probably get
          Message 4 of 11 , Jul 9, 2013
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            Thanks Jurgen.  I'll look over your work and probably get back to you with questions.

            Best - Ben


            On 7/9/2013 6:42 PM, Jurgen Bartels wrote:
             

            > I suspect the software changes would not be huge. Or, is there a way to
            > do this external of the SL source code. Any thoughts?

            You can write your own plugin, it works very well, I have made a few for my own
            purposes.

            Jurgen Bartels Suellwarden, N. Germany
            Ant. hor: 29-45MHz 7-el, 45-87MHz 11-el, FM 15.11, Band-3:13-el, UHF:48-el
            TV: Winradio G305 / Fly2000 + video noise filter & variable IF BW
            FM: Downconverter + Perseus + Speclab as WFM demod.
            MW: 30 x 4m EWE 320° with JB-terminator, Winradio & Perseus
            http://zeiterfassung.3sdesign.de/station_list.htm
            http://dx.3sdesign.de/tv_offset_list.htm


          • wolf_dl4yhf
            Hello Ben, As Jurgen correctly pointed out, you could do this with your own plugin (compiled into a windows DLL). Those plugins originally operated on
            Message 5 of 11 , Jul 10, 2013
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              Hello Ben,

              As Jurgen correctly pointed out, you could do this with your own plugin (compiled into a windows DLL).
              Those plugins originally operated on short-term fourier transforms of the FFT-based audio filter, but since a couple of years there are also callback functions (invoked by SL in the plugin DLL) to perform any kind of processing in the time domain (i.e. on the waveform data). The tricky task may be that you'll have to detect the periocity of a signal somehow; so a combination of processing in the frequency- *and* the time-domain may be required.

              The plugins are explained here:
              http://www.qsl.net/dl4yhf/speclab/filters.htm#fft_filter_plugin

              There is also a link to a sample plugin (written in 'C') in that document.

              All the best,
                 Wolf .

              Am 10.07.2013 01:07, schrieb M. Ben Schuetz:
               

              A few days ago I raised a question about "signals" with and without harmonics.  Since I have only been using SL in one way for the past couple of years, the other signal types weren't that familiar to me.  Graham and Wolf responded with thought provoking observations.  So, I made a few simple tests with a signal generator to explore the issue.

              Here's the situation.  A square wave or any periodic pulsed signals is coupled into the computer audio board through a 0.1 uF cap.  Given the internal resistance of the audio board, this results in roughly 100 us pulses.  SL responds to these showing approximately equal amplitude signals of all the harmonics.  If a pulse or two are missing here and there, the appropriate harmonic is enhanced.  The consequence of this is that any signal not having 2nd, 3rd, . . . harmonic bins are just noise and can be disregarded.  Hopefully, and even better, in software they can be discarded from any further processing.  That would bring the noise baseline down to about nothing while leaving a clean detected signal.
              It would obviate the need to look at waterfall clutter and improve the minimum detectable limits.

              This may have applications anywhere a periodic signal can be converted to pulses before going to SL.

              I suspect the software changes would not be huge.  Or, is there a way to do this external of the SL source code.  Any thoughts?

              Ben



            • M. Ben Schuetz
              HI Wolf, That s very helpful. I looked about for the plugin information, but didn t find it. With regard to detecting periodicity, won t a comparison of bin
              Message 6 of 11 , Jul 10, 2013
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                HI Wolf,

                That's very helpful. I looked about for the plugin information, but didn't find it.  With regard to detecting periodicity, won't a comparison of bin number contents be sufficient.  If not, never mind, this will take a bit of noodling to sort out. 

                Best - Ben


                On 7/10/2013 1:11 PM, wolf_dl4yhf wrote:
                 

                Hello Ben,

                As Jurgen correctly pointed out, you could do this with your own plugin (compiled into a windows DLL).
                Those plugins originally operated on short-term fourier transforms of the FFT-based audio filter, but since a couple of years there are also callback functions (invoked by SL in the plugin DLL) to perform any kind of processing in the time domain (i.e. on the waveform data). The tricky task may be that you'll have to detect the periocity of a signal somehow; so a combination of processing in the frequency- *and* the time-domain may be required.

                The plugins are explained here:
                http://www.qsl.net/dl4yhf/speclab/filters.htm#fft_filter_plugin

                There is also a link to a sample plugin (written in 'C') in that document.

                All the best,
                   Wolf .

                Am 10.07.2013 01:07, schrieb M. Ben Schuetz:
                 

                A few days ago I raised a question about "signals" with and without harmonics.  Since I have only been using SL in one way for the past couple of years, the other signal types weren't that familiar to me.  Graham and Wolf responded with thought provoking observations.  So, I made a few simple tests with a signal generator to explore the issue.

                Here's the situation.  A square wave or any periodic pulsed signals is coupled into the computer audio board through a 0.1 uF cap.  Given the internal resistance of the audio board, this results in roughly 100 us pulses.  SL responds to these showing approximately equal amplitude signals of all the harmonics.  If a pulse or two are missing here and there, the appropriate harmonic is enhanced.  The consequence of this is that any signal not having 2nd, 3rd, . . . harmonic bins are just noise and can be disregarded.  Hopefully, and even better, in software they can be discarded from any further processing.  That would bring the noise baseline down to about nothing while leaving a clean detected signal.
                It would obviate the need to look at waterfall clutter and improve the minimum detectable limits.

                This may have applications anywhere a periodic signal can be converted to pulses before going to SL.

                I suspect the software changes would not be huge.  Or, is there a way to do this external of the SL source code.  Any thoughts?

                Ben




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