Thermal drift stabilisation by software:Can it ne done?

1st Official Post

    A known issue with the Pluto is that its transmitting frequence drifts because ot the temperature rise during tramsmission. At 2.4 GHz, the drift can be several Kilohertz.

    There are a number of descriptions on the Web, and particularly on this forum, that show how to replace the oscillator of the Pluto with a TCXO. This corrects the issue, but these SMD components are really tiny, so this modification really needs sharp eyes and steady hands!

    So I wonder if it could be possible to minimize this frequency drift, using software. After all, SDR console does an excellent job compensating the LNB drift, by using the satellite's beacon as a reference.

    As receiver, I don't use the Pluto, I use a separate RTL SDR stick, so the Pluto's receiver does nothing.


    Could it be possible to feed a stable reference into the Pluto's receiver, such as a TCXO, OCXO or GPSDO, and have the software compare it with the actual transmit frequency? For this to be done, part of the Pluto's transmitter output signal should also be fed into the receiver, but maybe the parasitic feedthrough between transmitter and receiver should be sufficient at 2.4 GHz.

    The final result would probably not be as good as the TCXO solution, but maybe it could somewhat mitigate the problem?


    Now, I know that common wisdom says that "if you think you just had a good idea, be aware that there is probably someone who has had it before you. And if it was feasible, then someone has probably already tried it"


    That is the reason why I am asking my question on this forum. What do you think?

    • Official Post

    A very interesting thought but it likely needs dedicated firmware on the PLUTO FPGA. I don't think a software solution where the data first goes via USB to the host and then adjusts the TX frequency in real time would give satisfactory results.

    That said, a non-SMD component solution is to scrape the REF_FREQ line between the XO and the ADC and feed your external 10 MHz reference there. This has been documented widely and only does require /some/ soldering skills, nothing too fancy.