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Phase-Detector for Frequency-Standards Using AFEDRI SDR-net x2

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  • Larry Weber
    It recently occurred to me that my AFEDRI SDR-net x2 mightmake a very good phase detector to measure the Allan Deviation of GPS disciplinedcrystal oscillators
    Message 1 of 6 , 19 Mar
      It recently occurred to me that my AFEDRI SDR-net x2 might make a very good phase detector to measure the Allan Deviation of GPS disciplined crystal oscillators or rubidium frequency standards in order to test their frequency stability.  These high accuracy standards are essential for generating frequency stable signals in the microwave range.  This measurement needs to precisely measure the phase difference between two 7 dBm 10 MHz signals and record this at typically one second intervals for many hours up to a few days.  The output would be a text file with the once a second phase delay floating point numbers usually expressed as very small fractions of a second (nanoseconds of phase difference over the one second interval).  This text file could then be sent to free software such as TimeLab http://www.ke5fx.com/timelab/readme.htm to do the statistical analysis such as the Allan Deviation plot.

      If such a measurement would work well on the AFEDRI SDR-net x2 then it would be really valuable with the AFE822x4.   This would allow the simultaneous phase comparison of up to 4 frequency standards.  Comparison of 3 or more standards is quite useful since a single misbehaving standard can easily be identified when its errant phase is compared to the normal phase of the other two.  This cannot be done when measuring only 2 standards since it is not clear which one is misbehaving.

      My question to the group: what is the best software approach to accomplish the generation of such a phase difference text file?  I assume I will need to do some software work but I would like to use as many of the existing tools as possible.  I am not familiar with Linrad but is this a direction I should explore?  Or perhaps someone has already done this and can tell me how they did it.

      I would be very happy to hear any ideas or suggestions.

      Larry
      K9ZBU
    • sp2bpd
      Larry, two programs come to my mind: 1/ DL4YHF SpectrumLab - use Color Direction Finder configuration with Watch List and Plotter function. 2/ Linrad - use
      Message 2 of 6 , 20 Mar
        Larry,

        two programs come to my mind:

        1/ DL4YHF SpectrumLab
        - use Color Direction Finder configuration with Watch List and Plotter function.

        2/ Linrad
        - use Adaptive Polarization with Phasing Window.
        .
        The above is for 2 channels.

        I do not know about the 4 channels software.

        Maybe running simultaneously 2 instances of 2-channel software. But how to synchronize them - I don't know.

        Let us know what you discover. It is an interesting topic.

        Piotr, SP2BPD




        ---In afedrisdr@..., <larryweberplasma@...> wrote :

        It recently occurred to me that my AFEDRI SDR-net x2 might make a very good phase detector to measure the Allan Deviation of GPS disciplined crystal oscillators or rubidium frequency standards in order to test their frequency stability.  These high accuracy standards are essential for generating frequency stable signals in the microwave range.  This measurement needs to precisely measure the phase difference between two 7 dBm 10 MHz signals and record this at typically one second intervals for many hours up to a few days.  The output would be a text file with the once a second phase delay floating point numbers usually expressed as very small fractions of a second (nanoseconds of phase difference over the one second interval).  This text file could then be sent to free software such as TimeLab http://www.ke5fx.com/timelab/readme.htm to do the statistical analysis such as the Allan Deviation plot.

        If such a measurement would work well on the AFEDRI SDR-net x2 then it would be really valuable with the AFE822x4.   This would allow the simultaneous phase comparison of up to 4 frequency standards.  Comparison of 3 or more standards is quite useful since a single misbehaving standard can easily be identified when its errant phase is compared to the normal phase of the other two.  This cannot be done when measuring only 2 standards since it is not clear which one is misbehaving.

        My question to the group: what is the best software approach to accomplish the generation of such a phase difference text file?  I assume I will need to do some software work but I would like to use as many of the existing tools as possible.  I am not familiar with Linrad but is this a direction I should explore?  Or perhaps someone has already done this and can tell me how they did it.

        I would be very happy to hear any ideas or suggestions.

        Larry
        K9ZBU
      • alex4z5lv
        Hello Larry, Interesting application, but I do not know any SDR application that provides text information that you want. I suppose there is need to write
        Message 3 of 6 , 20 Mar
          Hello Larry,
          Interesting application, but I do not know any SDR application that provides text information that you want.
          I suppose there is need to write something special for this case.
          In connection to 4 channel AFE822x4 SDR - I suppose  there is only two utilities - SDR_Network_Control_box and command prompt Linux - sdr_split, that can work with 4 channel SDR, I know any other apps that can do that.

          73!
          Alex
        • larryweberplasma
          Thanks Poitr and Alex for the good suggestions that got me thinking. It would be best if I start with a software solution that will ultimately work with 4
          Message 4 of 6 , 20 Mar
            Thanks Poitr and Alex for the good suggestions that got me thinking.  It would be best if I start with a software solution that will ultimately work with 4 channels even though my initial tests will only be with 2 channel hardware.  So that leaves me with SDR_Network_Control_Box or sdr_split.  Today I took a look at both source codes to get ideas for a plan of attack.

            A prime concern of this project is phase difference measurement accuracy.  I probably need to process the received UDP packet stream directly to evaluate various algorithms for this accuracy.  In an earlier post on this list I ran across a suggestion to use the UDP Broadcast or Multicast options in SDR_Network_Control_Box to simultaneously send the UDP packet stream to Matlab.  This sounds very powerful since I could run HDSDR (or any other compatible ExtIO program) with SDR_Network_Control_Box which could control all 4 channels and simultaneously process the data with Matlab to generate the phase difference text files. 

            Does this sound reasonable?


            Larry
            K9ZBU
          • alex4z5lv
            Larry, Please pay attention to Leif s message about Linrad - it seams to me explaining the complete solution for your application. In connection to
            Message 5 of 6 , 20 Mar
              Larry,
              Please pay attention to Leif's message about Linrad - it seams to me explaining the complete solution for your application.

              In connection to SDR_Network_Control_box or sdr_split - it can be used only as start point or example how to control/implement and get data from  4 channel AFEDRI SDR, for sure you need to add your own digital processing to measure phase / difference etc...

              73!
              Alex
            • larryweberplasma
              Alex, Thanks for pointing me to Leif s comment. Sorry that I unintentionally created two threads for this one topic. I understand what you are saying about
              Message 6 of 6 , 21 Mar
                Alex,

                Thanks for pointing me to Leif's comment.  Sorry that I unintentionally created two threads for this one topic.

                I understand what you are saying about SDR_Network_Control-box and sdr_split.  I can learn a lot from reading your code.

                Larry
                K9ZBU
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