Posts by S59MZ

    pe1chl I tested what hapens when I add the external reference and what when I remove it. The beacon shifts for about 230 kHz lower on the spectrum and stops drifting. The previous beacon disapears completely. For the test beacon I used a 24. harmonic signal from my Baofeng ham radio tuned to 432 MHz. There was only one beacon in both cases.

    I also measure the signal on the crystal at both ends with an oscilloscope and compare it with the 10MHz from GPS in the XY-mode. I got nice and stable Lissajousse curve which means that the 25MHz signal was phase locked to the GPS.

    @Mike5000 The signal level is about 3Vpp. I experimented with 1nF at first, but I got very big phase noise. I don't know why exactly, probably because the reference signal level was too high. Then I tried with several smaller capacitances and got much better results. I found the optimal value 15pF for my case.

    In the picture above there are two added capacitors in serial, because I experimented with different values - just added lower capacitance to existed 1nF. In the final version I have only one capacitor 15pF (not shown on picture).

    My solution for LNB modification. I tried several different capacitor values, but 15pF capacitor works the best for me.

    I also noticed that the LNB sensitivity drops down for about 3dB. It is stlll acceptable for NB, but not for WB on a 80cm dish. I don't know why yet. For WB receiving, I just remove the SMA cable from LNB and it works without external 25MHz reference.

    I'm using PLL-GPSDO of BG7TBL from eBay:

    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).