sl3s + 21v pi + frequency sweep from 150mhz to 2150mhz

Discussion in 'DIRECTV General Discussion' started by tdbone1, Jan 21, 2019.

  1. Jan 28, 2019 #41 of 260
    slice1900

    slice1900 Well-Known Member

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    Why would you think you could use it for radio astronomy? The dish is WAY too small, it pulls in an area of about 2 degrees for Ka and maybe twice that for Ku. There's a reason why radio astronomers use huge dishes.

    If you still think you want to use a Directv dish for that purpose, throw away the SWM LNB and get a legacy LNB.

    I'll leave it to VOS to explain about how polarization further complicates your hope of using it for radio astronomy - you would be better off with a horizontal/vertical LNB :)
     
  2. Jan 28, 2019 #42 of 260
    HoTat2

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    Pardon any ignorance I may have of the latest in the field of RA ....

    But to receive the extremely weak cosmic signals over the tremendous astronomical distances involved. Doesn't it require humongous size dishes with ultra low noise LNAs based in a geographically RF restricted location somewhere?

    And even with such large dishes, isn't it customary to actually require a number of them arranged in big arrays using interferometry to create even larger virtual size dishes?

    So what can hope to be gained with only a DIRECTV 32" x 22" elliptical reflector and LNB for RA research?

    Sent from my LM-V405 using Tapatalk
     
  3. Jan 28, 2019 #43 of 260
    P Smith

    P Smith Mr. FixAnything

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    only our student can reveal all aspects of his project :)
     
  4. Jan 31, 2019 #44 of 260
    tdbone1

    tdbone1 Member

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    M2, Hydrogen line and ....
     
  5. Jan 31, 2019 #45 of 260
    slice1900

    slice1900 Well-Known Member

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    You'd need an LNB able to directly pick up ~1400 MHz signals, not one that picks up 12.2 - 12.7 GHz (etc for Ka) and downconverts them to 950-1800 MHz "ish" range.

    Directv's LNBs would be 100% useless for trying to receive something on the hydrogen line.
     
  6. Feb 1, 2019 #46 of 260
    P Smith

    P Smith Mr. FixAnything

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    btw, what is "M2" object ? Stars constellation ?
     
  7. Feb 1, 2019 #47 of 260
    dreadlk

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    Interesting topic.
    The AIM meter creates a spread sheet showing the data for each transponder on every satellite. You can see the Freq, deviation, strength in -dbm and signal quality.

    I have a 3.2Ghz spectrum analyzer at work that I plan to bring home. I figure a conventional 0-2250 MHz splitter between the receiver and the SWM output will leave me with a port to tap into and see how the SWM module behaves when the receiver changes channels and sats. I could also substitute the AIM meter for the receiver and have greater control.

    They are right about the noise floor. An SDR is great for seeing what is there but without the noise floor info you cannot calculate the signals power. Also if I Remember correctly the noise floor is around -40dbm.
    on SDRs so That’s why the data cannot be used for measurement.

    My spectrum analyzer can go down to -140 dbm
     
  8. Feb 1, 2019 #48 of 260
    P Smith

    P Smith Mr. FixAnything

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    Nope.
    You can't control without knowledge of SWiM interface/protocol.
    Only observe.
     
  9. Feb 1, 2019 #49 of 260
    P Smith

    P Smith Mr. FixAnything

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  10. Feb 1, 2019 #50 of 260
    slice1900

    slice1900 Well-Known Member

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    With observation, it would be simple to deduce the protocol. It can't be that complex, given that it has a bit rate of only 38.4 Kbps.

    You couldn't decode that FSK signaling into binary/ASCII with a spectrum analyzer of course, you'd need something like a SDR...
     
  11. Feb 1, 2019 #51 of 260
    P Smith

    P Smith Mr. FixAnything

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    So? How about stay on real base ? He have just the SA..."observation" my tongue give more :D
     
  12. Feb 1, 2019 #52 of 260
    dreadlk

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    Not sure if I understand what your saying. I just want to be able to observe how the SWM behaves to different channel changes and then look at the spectrum it produces. As for decoding the control signals relayed between receiver and SWM I could do that but I don’t see what use that info is to me. Probably easier to reverse engineer an old SWM 8 with a scope and logic probes but once again what would I do with the info?
     
  13. Feb 1, 2019 #53 of 260
    dreadlk

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  14. Feb 1, 2019 #54 of 260
    P Smith

    P Smith Mr. FixAnything

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    Real geek will never ask such questions :)
    See Karl (?) Cimmerman's research of dish legacy switches protocol.
     
  15. Feb 1, 2019 #55 of 260
    P Smith

    P Smith Mr. FixAnything

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    then I didn't get what that quoted your phrase mean ...
     
  16. Feb 1, 2019 #56 of 260
    P Smith

    P Smith Mr. FixAnything

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    if you'll by follow the URL, you'll see what is there
    perhaps that RF chip's specs have the number, but I didn't read all docs
     
  17. Feb 1, 2019 #57 of 260
    slice1900

    slice1900 Well-Known Member

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    Who cares about the difference between 40 db and 110 db SNR for this purpose? Directv's transponders operate individually with a ceiling of about 15 db SNR. From the weaker to the strongest it is about 25 db SNR. Everything you want to learn about Directv can be learned with a device that maxes out at 30 db SNR.

    Devices with 100 db SNR have their purposes, and surely cost more, but they aren't needed where Directv is concerned.
     
  18. Feb 1, 2019 #58 of 260
    veryoldschool

    veryoldschool Lifetime Achiever Staff Member Super Moderator DBSTalk Club

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  19. Feb 1, 2019 #59 of 260
    veryoldschool

    veryoldschool Lifetime Achiever Staff Member Super Moderator DBSTalk Club

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    Resolution BandWidth

    Needs to be known


    This ends today's class in using Spectrum Analyzers
     
  20. Feb 1, 2019 #60 of 260
    dreadlk

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    Huh?
    The RBW is controlles on the spectrum Analyzer. Mine will go down to 1Hz but then it takes forever to do a sweep. The lower RBW will of course make the Noise floor lower and also separate more of the different components of the signal. I am not sure what it is that people are trying to accomplish so maybe they need an MDO scope for their purposes.
     

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