SSB signal is scratchy, depending on the LNB? [solved]

  • Dear all,

    while trying to receive signals from QO-100, I observed a strange problem: the audio of the SSB signal is extremely scratchy, depending on the LNB.

    Before identifiying the LNB as the culprit, I changed the SDR radio (Adalm Pluto vs. RTL Dongle), the software (SDR Console vs SDR Angel, including the latest updates), the DC source and I checked the Bias-T. I even changed the cables. Only after trying the third LNB, I had a clear audio signal.

    What puzzles me is that two (Bullseye and a standard consumer LNB) out of three LNBs in my sample generate scratchy signals. Therefore, I assume that this might not be an uncommon problem.

    Is there anybody who observed a similar signal and behaviour? Is there a way to solve this problem? Could it still be a software problem? Configuration? Help and ideas are highly appreciated. The reason why I'm asking is that I would like to work with the Bullseye. The one which works is not stabilised, yet.

    73 de Timo

  • Are you saying only the unmodified lnb receives "normal" ? What source do you use for the 25.xxMHz? Oscillator removed from lnb and replaced with tcxo or external source?

    I believe your reference jitters a lot.



    • Official Post

    Hallo Timo

    Welcome in our world, this was the first problem we had to solve. You can find hundreds of discussions about LNB's in this forum. If your working LNB is from Opticum or a similar model, use this one. You can use it without modification with SDR console. i use one from Opticum with my old Kenwood TS-711E without any problem. But you are free to modify any LNB.


  • Please tell us your lnb's brands, models and wether modified or not. Also the modification method.

    Since the unmodified lnb works as it should and given the power supply for the modified lnbs does not break down, it's likely the modification.

    Did you modify yourself or did you buy modified? If the latter, have the vendor(s) / modifier(s) check the modified lnb(s).



  • Quick test: If you inject 18V instead 14V (you DO feed 14V , do you?) and rotate the scratchy modified lnb from it's vertical position to horizontal, is it still scratchy? If not, your problem is the power source.

    73, Martin

  • Thank you very much for sharing your ideas. So far, I have tried the Bullseye LNB which is supposed to work out of the box (I did not modify it by myself, it comes with a TCXO and is designed for QO-100). The two unmodified LNBs are a hb digital UHD 101S and a Skymaster. The UHD101S works (but it drifts of course).

    dm4im: Actually, I feed 12V and not 14V. The Bullseye is supposed to work in vertical polarisation from 11.5V-14V. But maybe 12V are not enough. 14V are worth a try.

  • Some LNBs need a VERY clean powersupply.

    In case that most of the LNBs have internal voltage regulators at 6 volts (like 78L06) , one can power the LNBs with voltages down to 8 volts. (which also keeps them nice cool)

    So it's possible to use 12 volts from the rig and filter it in an additional voltage regulator to 8 / 9 volts for example 7808 or 7809

    This gives a very clean LNB supply.

    And don't forget the capacitors at the regulator.


    Armin DF1QE

  • Problem solved! Thank you very much for your suggestions.

    A LTE/4G filter (which is nothing else but a ~790MHz low-pass filter) solved all my reception problems. Apparently, there was some unwanted hf from the surrounding cell sites affecting my QO-100 signal.

    I noticed that some LNBs (including the one which had worked in my case) have an in-built LTE/4G filter. But some LNBs don't...

  • DB8VB

    Changed the title of the thread from “SSB signal is scratchy, depending on the LNB?” to “SSB signal is scratchy, depending on the LNB? [solved]”.