2.4 GHz PA from Bisonelectronics

    Hi OE3GBB,

    Quote from OE3GBB

    Hi Thomas, I have the same problem. I do have a double unit and do want to combine them for double power. The right amplifier is doing well, but the left one is oszillating. Did you find a solution yet?


    No, no solution until now.

    I disabled the onboard bias voltage and fed it from external. So I'm able to slowly increase it from 0V on. But at some point around 1,7V the circuit begins to oscillate.


    Another try was to make the input impedance better through cutting the trace after the input isolator and soldering a small coax cable with 50Ohms in there. Circuit still oscillates.


    Used one FET or two FETs at the same time. Circuit still oscillates.


    I'm really frustrated. Both modules I'm having here are oscillating. Not only one ist stable.


    Next try is to clean the downside of the pcb and the heat sink for giving a better ground potential. Maybe there is some oil from the milling machine left there. I've done that before but now I'll do it again very exactly.


    Did you had a look at the other thread (https://forum.amsat-dl.org/index.php?thread/51-what-tx-amplifier-do-you-plan-to-use/) here? It seems, some guys there are having also the same problem as we are having.

    Quote from DH1DA

    @G8UGD

    Adrian, many thanks for your prework and especially for your bias schematic, this was really helpful to check, whether there was a problem with the circuit.


    Armin

    I am pleased my time has helped, and even more pleased that you have taken it further and made life that bit easier with your work, thanks for that. I am not into arduino programming so that was probably above me.

    I have no solutions on the self oscillation of the units, I did have one that was lively on power up, but put that down to to much heatsink compound, now I only have a minute dab of it in the very centre of the devices. I removed the input circulator and 2.2Ghz filter and replaced with co-ax, had to then solder that down to the board or it acted like a pick up loop and caused some instability, but has been generally quite good. Only thing I can think of if you still have the output circulator fitted is to make sure that is still a very good ground on it's case, if you have removed the circulator from the output, then most take the power from the input to the circulator rather than the original connector, but others have gone different ways from what I can tell. So I tend to think it could be what ever works for you with that, try dropping to 26 Volts from 28 and see if that helps any???

    Hi all,


    just a short update from my workbench:

    My amplifiers are working now and they do not oscillate anymore. :)
    What I've done, was:


    - complete dismount the board from the heat sink
    - removed output circulator and both transistors from the board
    - cleaned all of them (circulator, transistors, board AND heat sink) very carefully with alcohol
    - mounting the board with all screws (changed to M2.5x4mm) on the heat sink
    - mounting and soldering output circulator
    - mounting and soldering transistors (bend the gate and drain pins to get good contact!) as mentioned by ra3s in this article
    - Implement the common BIAS voltage modification as explained by DH1DA in this article

    - connecting the GND from the power supply only to the heat sink


    I used a 10kOhm multi-turn trim pot to be able to set the BIAS voltage very exactly.

    I believe, in my case there was some residue from adhesive tape (used to fix the output circulator to the board for transport) on the circulator and the board. This and some small gaps between the transistors and the heat sink are responsible for having no perfect ground connection at those elements.

    So many thanks for all those helpful postings here, guys! :thumbup:

  • DB2OS

    Changed the title of the thread from “Can I just ask about a PA from Bisonelectronics.” to “2.4 GHz PA from Bisonelectronics”.

    Hello, I know this thread is very old but I am just now receiving one of these PAs. I wanted to ask if anyone has photos of the inside of the top cover? I can only find a low resolution image. I'm going to mill out a cover for it and wanted to check if there are any RF absorber pads or other structures in the cover. If anyone does have a cover that's easy to measure I'd be very interested in how deep the cover is (how tall the side walls are).

    Thanks!