solved-Leo Bodnar GPSDO Output waveform

  • Hallo,

    ich bin neu hier und grüße alle OM . Mein Name ist Henry DH5RUM.

    Ich besitze eine Mini GPS Referenz Clock von Leo Bodnar.

    Letztes Wochenende wollt ich in deine umgebauten

    Octagon Quad LNB die Referen 25 MHZ einspeisen.

    Ergebnis : Der LNB funktionierte nicht. Kabel alle Okay.

    Unmodifizierter Oktagon Quad LNB funtioniert auf allen

    4 Anschlüssen.

    Ich habe das Sinal des GPSDO mal geprüft.

    Sieht komisch aus. Ist das so in Ordnung?

    Falls ich was hier im Forum falsch gemacht habe, ruhig Bescheid sagen!

    Danke für Eure Hilfe.

    73 Henry

  • Welcome Henry !

    (this is the english section of the forum, so I reply in english that other can profit from this thread as well)

    I don't have this particular GPSDO but to me the pulseshape looks quite nice. Check again with a 50 ohm termination because I think that is what the Leo Bodnar GPSDO expects. Generally, rectangular signals for these low frequencies are better suited (some PLL chips even require them instead of sine wave inputs).

  • DB2OS

    Changed the title of the thread from “Leo Bodnar Amplitude sauber?” to “Leo Bodnar GPSDO Output waveform”.
  • Leo Bodnar GPSDO is not Sine Wave output - see data on their website...

    Both output signals square wave at 3.3V CMOS levels with 50 Ohms characteristic impedance. Their output drive levels can be adjusted and outputs can be enabled and disabled independently.

    Output power level (measured at 10MHz, fundamental power channel):

    +13.3dBm, drive setting 32mA

    +12.7dBm, drive setting 24mA

    +11.4dBm, drive setting 16mA

    +7.7dBm, drive setting 8mA

    Its mentioned here:…duct_info&products_id=234

    So all is 100% OK, hi hi...

    73, Oscar

  • I also recommend a low- or bandpassfilter. Else you "spread" your whole shack with a ladder of 25 MHz harmonics if your cables are not well screened. And your neighbour will like it :-)

    (In our region there is a loved radio broadcast on 100 MHz)

    But another question :

    Does not all Oktagon LNBs use 27 MHz reference ?


    Armin DF1QE

  • That's why there is a low pass filter built into the BATC Reference / DC injection IF out board. You also find the 25MHz will overload your SDR if you use the single coax method and don't filter it out.

  • I don't think the lowpassfilter is a matter if the LNB sychronises or not.

    As DH2VA already wrote, the PLL synchronizes best with a high (but not to high) slew rate.

    But the signallevel matters in some LNBs a lot.

    Usually the x-tal oscillates with a level of around 0.5-1.0 Vss.

    If you drive it externally with more than 1.0 Vss, some LNBs don't like it.

    Then the DC-Level on the OSC out pin drops very low and the AC curve gets limited at ground or a frequency doubeling occurs.

    You can easyly test that by inserting a potmeter (around 100 Ohm) as a voltage divider in the REF line.



  • DH5RUM

    Changed the title of the thread from “Leo Bodnar GPSDO Output waveform” to “solved-Leo Bodnar GPSDO Output waveform”.
  • How did you modify the LNB ?

    1. there must be a DC decoupeling by a capacitor (around 1 to 10 nF)

    2. there must be a termination to Ground of around 75 Ohm


    Armin DF1QE