My first TX to QO-100, is this off frequency and drift normal for stock Pluto?

  • I got my Pluto mounted at the dish, which is a 1.8 meter PF. I have only opened up the Pluto frequency width and enabled both processor cores in the firmware, which is V0.33. Th Pluto xtal oscillator is stock. I ran it into the AD CN-0417 pre amp that I was going to use to feed my SG Labs 20W PA. For testing I thought I would see if the satellite could hear me just using the CN-0417 output direct to the POTI, I did not expect it would...


    The software is SDR Console, locked to the beacon, and it "talks" to the Pluto via an ethernet cable and ethernet to USB at the Pluto. In SDR Console I have an RX offset of 9750MHz set and a TX offset of 6089.5MHz set. Is this TX offset correct please?


    I TX'd an FM signal with the software set to 10.489730 I could indeed see my signal on the UK based Goonhilly web SDR,, but it was way off frequency, and drifting in steps. Is this to be expected until I muster the courage to try and remove the stock oscillator and feed the PCB with a GPS locked 40MHz from my Leo Bodnar GPSDO?


    Given the signal strength from just the CN-0417 (although I am unsure if it's linear at that level), once the frequency issue is sorted, might I even be heard on SSB without the PA?


    Thanks for any advice. Chris, call sign 2E0ILY

  • Hallo,

    it would be nice to know your name.
    If the receiver is locked to the PSK-Beacon all is fine for receiving.
    The only oscillator which has influence to the transmit frequency is the 40mc clock on the Pluto board. While transmitting the board warms up and the oscillator starts drifting. Either you change it to a better one or use Leo Bodnar GPSDO. A possible shift should be changed with XIT-function of the Console. Don't use any calibration.
    When using the 500HZ-tone of the Console, you can compare the transmit and the received frequency to achive beating while adjusting XIT.
    Have fun.
    73
    Andreas

  • Thank you Andreas and Detlev for your replies, much appreciated. Andreas, I edited my post, my name is Chris, sorry! I should add a sig I think!


    Unfortunately Mouser sent me an earlier Rev. B so I will have to do surgery on the PCB. If I get the oscillator off OK I may attempt to solder a u.FL connector pad to the board as I have seen done on some Google photos. I have the connector pads and some suitable short coax links, SMA female bulkhead to u.FL.


    I have successfully fitted SMC oscillators of similar size to new PCB's in the past, but I tend to be a bit unlucky REMOVING such things leaving the PCB in a reusable state ;) Having seen how bad the stock oscillator is for such demanding usage as ours, I need to just go for it and see what happens. Thanks again.


    Best regards, Chris Wilson.

  • Hi Chris,

    thanks for introduction.

    If you decide to change the oscillator, don't put it back to the original pads. It is much better to have a thermal isolation. I used a very small board just to solder four wires to the original place. There is a whole, closed to the solder pads. Stick the wires though to have the oscillator free hanging below the main print. Temperature influence of the main board is reduced. A little fan above the heat sources can be helpful too. Otherwise a "Leo" is much better of course.

    For removing the original oscillator use two irons and some more tin around the chip. The lead free tin is horrible. Turn the irons to more heat and you will remove the Chip within seconds.

    73
    Andreas

  • Hi Chris,

    thanks for introduction.

    If you decide to change the oscillator, don't put it back to the original pads. It is much better to have a thermal isolation. I used a very small board just to solder four wires to the original place. There is a whole, closed to the solder pads. Stick the wires though to have the oscillator free hanging below the main print. Temperature influence of the main board is reduced. A little fan above the heat sources can be helpful too. Otherwise a "Leo" is much better of course.

    For removing the original oscillator use two irons and some more tin around the chip. The lead free tin is horrible. Turn the irons to more heat and you will remove the Chip within seconds.

    73
    Andreas

    I will be using a Leo Bodnar GPSDO as the reference once I remove the xtal oscillator, so that should not be affected by temp changes in the box? Thanks Andreas. Chris, 2E0ILY.

  • Good afternoon, name is Carlos and call sign M0HBK and this is my first post in the forum. Following on Chris' question, I just received my Adalm-Pluto from DigiKey and the board is a rev D. I have ordered a Mini Precision GPS Reference Clock from Leo Bodnar as well as the cables to interconnect it to the Pluto. So far so food.


    Now, I have been searching around for the specifics on how to set this up and I was wondering if someone that has done it can provide some direction and advice:


    1. Assume that the signal from the GPSDO is connected to the connector labelled CLK-IN on the Pluto board

    2. I am looking for the required command(s) to switch the Pluto to the external reference oscillator and set the frequency (assume 40 MHz)

    3. Also looking for the programming details for the Leo Bodnar Mini Precision GPS Reference Clock. Assume that it is best to stay with the 40MHz and from the note next to the CLK_IN connector on the Pluto board it states max 3.3V


    Appreciate any hints that you might have and also if you can point me in the right direction. I was able to make my first two QO-100 QSOs this afternoon but I can tell that my TX was drifting and want to get it fixed.


    Many thanks and 73, Carlos M0HBK

  • Hello Chris,


    I plan to make exactly the same setup as you do, so I will be following your messages :-)


    Just for your reference: there is a way to 'stop' the xtal oscillator in the Pluto by grounding the enable/disable pin of the xtal. This way you don't need to remove it from the PCB and you don't risk damaging the board.


    Credits to F4DAV for this modification.



    73,

    Lieven ON8HZ