NB Station for Es'hail-2

  • So long as you can receive one or other beacon within the passband (and it's CW), a single stick software drift connection is possible. I have some gnuradio code that does just that (although I'm using my Ettus USRPs, but the same code could be used with a dongle


    Whether a tablet would appreciate the extra overhead of gnuradio is another matter of course.


    For those interested, Basically I take 250k of B/W, Filter and Decimate around the 'beacon', then send to a FFT, measure the 'strongest' bin, calculate what that frequency is, compare against the 'correct' frequency, and send the difference back to the USRP or Frequency Translating FIR Filter (otherwise known as the Virtual Big Tuning Knob!)


    In the case of a dongle, it would need to be the FIR Filter, as the drivers in gnuradio don't let you change the frequency of the device once set without stopping and restarting the flowgraph.


    Note, my code will go down to 250mHz (Yes, milliHertz). Overkill, yes (although not for some of the experiments I intend to do), but remember that when the beacon is in PSK mode, there will of course be frequency shifts every time the phase changes to deal with. I'm hoping at least one beacon will always be in CW mode


    Iain

  • Now the software drift correction also works fine with weak master signals like the lower engineering beacon at 10-12dB S/N.

    Hi DL3DCW,

    i managed to get my 2 Stick solution to work with a reference signal level <6db.

    Even the now weaker lower EB is locked without problem.


    VY73 DB8TF

  • I think that my "quick-and-dirty" raspberry solution will work even with weaker signals less then 10dB S/N. But i have not tested it yet. I am very satisfied that the software correction works so well. And i am sure that there will be many better solutions in the future. It's very exciting ...

  • g7iii : Very interesting! Concerning the necessity of a CW carrier/signal, I wonder if a PSK-beacon couldn't be used too? E.g. by locking to one of the (known) carriers, some 'averaging' & 'secret sauce' , assuming the beacon is 'bang on' frequency of course.

  • DL3DCW

    It is a nice solution !

    Is it working with another sdr sticks than nooelec ? like standard rtl-sdr sticks

    Do you need some beta testers ? If you have a sd file image to share I can test if you agree.

    Thank you.

    73's

  • You can use all SDR sticks based on rtl-sdr driver. I am using the NESDR Nano 3 (0,5ppm) from NooElec because they are very small and so they fits perfect to my raspberry.


    I will post a info here in this forum if a first SD card image is available.

  • If the AMSAT beacons are stable and suitable for our solution this will be very attractive. In this case everything could be solved with only one SDR stick.


    However, using a separate SDR stick the system will be completely independent from the AMSAT beacons. So any stable signal from the sky can be used as master.

    For the TX chain i see not so big problems. My transmitter and my up converter both have TCXOs and will be operate at relative constant room temperatures. So they are not exposed to extrem sun, wind and weather like the receiving LNB.

  • Also i like to participate in this project. Will order 2 SDR sticks as well as a raspberry pi just now. Hopefully everythings will work fine after the opening party at the groundstation of Amsat-DL.

  • I am still searching for somebody who can write a sdr# plugin for the 1-stick solution, or for any other SW running on M$.


    Simon from SDR-Radio said he will look at a this function for his SW but that takes some time and he has much more features to implement prior to this.


    My 2PC + 2Dongle + external controller solution works well but a easier solution would be great.


    vy73 DB8TF

  • YL3AKC  ;-)

    If everything works fine i will create a sd card image for raspberry pi (like HAMServerPi). That makes it a little bit easier.


    Alternatively everyone can create his own solution for other systems by using/modificating the files/sources from sd card image. And makes it better then i can do ;-)

  • i managed to get my 2 Stick solution to work with a reference signal level <6db.

    This morning the lower EB is very weak (snow on the antenna?). The drift correction works anyway. But the master sIgnal should not be much weaker than 6dB S/N. I think this is very good for the simple solution.