What GPS module with 10 MHz or 25 MHz out for stabilizing the LNB local osc?

  • What GPS module do you recommend for generating a stable 25 MHz signal or alternatively 10 MHz signal to stabilize LNB drift?


    I have done some experiments with uBlox 6. However, it appears to have max. 24 MHz out and it was sort of a hack taking the signal off the led output. I would like something more reproducible and I would like to avoid buying surplus GPSDO components off ebay.


    • What GPS modules / breakout modules do you have experience with? Example: Sparkfun, Adafruit etc...
    • Are there GPS modules from uBlox that can directly generate 25 MHz?
    • Are there better suited GPS modules than the series from uBlox (that doesnt cost a lot)?

  • I'm using PLL-GPSDO of BG7TBL from eBay: https://www.ebay.com/itm/163109074276


    Then I open it, added another SMA connector to the bacplane and add a smal PCB protoboard with NB3N502 IC device, which multiply the frequency with 2.5 to get 25MHz.


    The IC device uses 3.3V, which is already inside the box and 10MHz clock square wave taken before LC filter on the BNC connector.


    I also add a 50 ohms resistor between output of NB3N502 and SMA connector for proper termination. Inside of LNB I aded a 15pF capacitor on one pin of the 25MHz crystal for decoupling.


    The phase noise is acceptable for CW, but I noticed that sensitivity of LNB dropped for about 3dB (not acceptable for WB).


    https://www.ebay.com/itm/152974650491

  • Hello Mike5000


    i use the dual output gpsdo for years now, and it works FB for me. 2 different output sigs are possible, independent programmed. For example, 1 output locks 3 transverters simultaneously on 10MHz with a 4 way output splitter,the second output gives me 25.7.....MHz to lock the lnb for rx on 439MHz. I also have a G3RUH GPSDO with 1 10MHz output to a 4*10MHz splitter.


    Jerry

  • Hi all, I am more looking towards what GPS module to be used for a DIY design.


    For example: do we need to use the special uBlox timing devices, or can we use a more generic uBlox 7 and use the PPS pulse output configured to xxx MHz. What is the best output frequency to avoid jitter etc.

  • Mike5000 You need to be careful about using standalone GPS modules. By its working principle, the PPS output of any GPS module has some serious jitter (good one in the 10s of ns range), even the timing modules. To get the best of both worlds, any GPSDO needs two key components, a low-jitter timing module for the long term stability(>100sec) and a flywheel crystal oscillator (often OCXO) which determines the short-term stability and SSB phase noise. Rick Hambly W2GPS together with Tom Clark W3IWI have written some excellent presentations on it: www.gpstime.com (disregard the expired SSL certificate for now).

  • ON4BCB : correct .. an experiment by a friend of mine confirmed this. But ... there was an issue with the purity of his 10 MHz itself, but the result was more than horrible.

    To be investigated/continued ...

  • Hi first steps to sattelite so i make only the RX so far. I use 80cm dish and the twin octagon pll. But notice the freg isn't stable. What can i do, what is my next step so the freg be stable.