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10 MHz Ref Input

W7QEX Member ✭✭

There isn't a way to determine if a 10 MHz reference signal is actually connected and if the signal strength is adequate. I am using a frequency standard that exceeds the GPSDO receiver capabilities in several ways. I would like to see an icon that verifies which ref is being used and if the signal strength is adequate.

2 votes

Open for Comments · Last Updated


  • KD0RC
    KD0RC Member, Super Elmer Moderator

    If you go to Settings, Radio Setup, RX tab you can see what the radio is doing with your 10 MHz f=reference signal.

  • Martin Bérubé
    Martin Bérubé Member ✭✭

    Is there a way to mesure the 10 MHZ INPUT signal strength. Is there some kind of meter or command in the Flex api that could be leveraged?

    I got an external 10 MHZ reference installed and it is constantly switch between it and the internal TCXO. I am wondering if the 10mhz signal is strong enough.

  • KD0RC
    KD0RC Member, Super Elmer Moderator

    Hi Martin, I don't know of such an API command. An oscilloscope or spectrum analyzer would let you know for sure.

    What happens if you change the selection from Auto to external reference?

  • Martin Bérubé
    Martin Bérubé Member ✭✭

    Hi Len,

    Thanks for the quick answer. I did try with a cheap PC oscilloscope but I don't really trust the readings.

    The lock is maintained when selecting the external reference. So it seems that the radio is somewhat accepting that reference.

    This is a GPSDO that I build myself around an OCXO. The design was picked op on youtube.

  • Mike-VA3MW
    Mike-VA3MW Administrator, FlexRadio Employee, Community Manager, Super Elmer, Moderator admin

    Section 40.8 of the SmartSDR Manual

    The radio monitors each of the inputs and indicates which have a signal present with the blue marker. The Temperature Compensated Crystal Oscillator (TCXO) is part of the radio hardware and is always available. When one of the three inputs is selected, using the menu shown above, the radio will use that input regardless of the presence of a signal. The master oscillator status is shown to the right of the selection list. When the master oscillator is trying to lock to the selected input, the status message will say “searching”. When it is locked, it will say “Locked”. 

    In Auto mode, the radio monitors each of the inputs and selects an input that offers a signal in priority order. The highest priority signal is the External 10 MHz signal (optional), followed by the GPSDO signal (optional), followed by the TCXO signal (always provided). The radio will track changes in the availability of the signals. For instance, if the External 10 MHz signal appears, the radio will switch to it from the GPSDO or TCXO signal. 

    If it is switching back and forth, then you have a problem with the supply reference signal. Try adding a 10 or 20db pad.

  • Martin Bérubé
    Martin Bérubé Member ✭✭

    Not sure about the pad. Using a much shorter cable. I can get a good lock on the external 10Mhz. So I see is 2 options:

    Find a way to amplify the signal or

    Rearrange the shack to have all my gear that requires a GPSDO near the reference.

  • Martin Bérubé
    Martin Bérubé Member ✭✭


    I just replaced a coax between the OCXO and the main pc board of my GPSDO. I now get a strong External 10 Mhz lock on the Flex.

    Conclusion: there was to much loss in my setup. Replacing the coax with a one offering a better performance fixed the issue.

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