Keep both internal and external reference on LNB

  • Has anyone ever managed to keep the internal 25MHz LNB crystal and inject the external GPSDO disabling the internal ref.?

    My goal would be that the LNB runs on internal crystal if no external ref. is provided, otherwise it runs on external reference source.

    This is because I found that WB RX suffer a lot of phase noise, even with the Leo Bodnar GPSDO I have a noticeable difference in received quality between modified and unmodified LNB. Of course this is not an issue for NB SSB.

    Any suggestion is welcome! Thanks, Mauro IW3ROW

  • Hello,

    IIRC there are some lnb's with 2 tcxo's and 2 pll circuits onboard. Can anyone confirm this? Or was there 1 TCXO, but 2 PLL circuits. If the first applies, remove one tcxo for the use of NB Transponder and inject external 25MHz. Keep the other one installed for the DATV-Transponder.

    73, Martin

  • HB9SKA

    Changed the title of the thread from “Keep both internal and external referece on LNB” to “Keep both internal and external reference on LNB”.
  • Thanks all for the suggestions.

    Martin, yes the Octagon twin lnb green has two separate oscillators, so your idea maybe feasible. If I want to use a unique cable I could use a diseq switch for example.

    George, I've read something similar and I've tried, but I never managed to get it working as expected.

    Mauro IW3ROW

  • Should this be possible with single LNB's? I tried this with Octagon Single, with BPF L-C from F-conn to xtal (pin20 on RDA3560), only works OK with external ref, nothing with internal xtal. Disconnecting the BPF from xtal, it works normal with internal xtal. I think i look something overhead or miss a clue.


  • Maybe the BPF is too big a load for the internal oscillator, it prevents it from operating. I use a similar method to feed external 116MHz into my 2m transverter via a Resistor and a Cap. I leave the internal oscilator in place while i feed from external source, but the internal oscillator stops working when i do this. It resumes work when i unsolder the C and R combination.

    73, Martin