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Can an external GPSDO be used with a 6400? If so, what type of interface is required?

Since the GPS connectors on the back of the radio are just blank plugs, some sort of interface must be required to to feed the GPS data (10 Mhz, etc) to the radio. This should be a very simple interface. The problem is obtaining the pinout data of the GPSDO socket on the 6400. Does anyone have information that would help?

Best Answers

  • KD0RC
    KD0RC Member, Super Elmer Moderator
    Answer ✓

    That hole is for a jack that connects to the internal GPSDO if you have that option. This is the 10 MHz IN RCA jack:

  • Lon Cottinghas
    Lon Cottinghas Member ✭✭
    Answer ✓
    Sorry guys, I jumped the gun. I was focused on the other plug. Thanks for the help and please forgive my oversite. 73 de Lon, K5JV
  • KD0RC
    KD0RC Member, Super Elmer Moderator
    Answer ✓

    No Worries Lon. There is a lot going on with these radios.

    Can you do me a favor and un-reject the answer that I gave?


  • KD0RC
    KD0RC Member, Super Elmer Moderator
    edited February 2022

    Hi Lon, There is a 10 MHz IN RCA jack on the back of the 6400. Any of the popular GPSDO units that provide a 10 MHz sine or square wave will work (check the manual to be sure that you are feeding a safe signal level to the Flex). Just plug the output of the GPSDO into the 10 MHz IN jack and you are good to go. No other interfacing is needed. I use the Leo Bodnar unit, and it works great.

    You will want to set your 10 MHz reference to Auto or External 10 MHz. I leave it on Auto so that I don't have to switch it when I take my Flex camping. Make sure that the External 10 MHz Locked check mark comes on. If not, you may have to orient your GPS antenna differently, or make sure that you have a proper 10 MHz signal level.

    If you use the GPSDO, either set the Offest to zero, or run the calibration routine (Start button). In my case, above, you can see that it wanted -2 ppb. There is no practical difference between zero and 2 ppb as it is a small fraction of a Hz. I ran this just to see what it would do. Since I live within 50 miles or so of WWV in Ft Collins, doppler effects of propagation are minor and that is what I attribute the 2 ppb to.

    A GPSDO is not really required for a Flex 6000 radio, as the calibration routine is REALLY accurate (assuming that you can hear a good frequency source like WWV). I got mine for use with my spectrum analyzer, and just leave it hooked up to the Flex since it is in the shack anyway.

  • Now, I am really confused. The 10 Mhz plug on the back of the 6400 in just a plank plug. It is not connected to anything inside. Also, it is marked "10 Mhz OUT".
  • KD0RC
    KD0RC Member, Super Elmer Moderator

    Here are the required min and max signal levels for the 10 MHz IN port.

    Just make sure that your GPSDO can be set within this range (the Leo Bodnar unit has a utility that can do this).

  • Larry _ NY8T
    Larry _ NY8T Member ✭✭✭

    10 mhz in is an rca connector next to the usb ports.

  • Found the correct plug. Tnx

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