Can I just ask about a PA from Bisonelectronics.

  • I think I need some assistance!


    I have had a near panic today. The power supply came in, I made up a few more connectors, I modified one unit and mounted it on the heat-sink and tried to do a few tests. Powered it up and the current through my meter was 4.5 Amps instantly, nothing seen on the Speccy An so I keyed a signal on the input to the amp and instantly saw an output at 2.4GHz current at 12 Amps!!!!

    To say that the dummy load and heat-sink got hot very quickly was an understatement, It turned out the unit was spurious with no input and taking 300 watts from the PSU.


    I sat down and had a rethink on things as one does. I removed the board from the heat-sink and removed all the heat-sink compound between the PA devices and the aluminium, the surfaces are smooth and I probably stuck a bit to much in there. Any way after cleaning it all off and reassembling it all back together, another attempt.


    This time quiescent current of 0.86 Amps and transmit current of 4.6 Amps with 2 Watts drive and clean output into the Speccy An.




    The set up is above, the picture shows the BU500 going through a 30dB directional coupler, it should be just under 2 Watts, and the -30 dB output to the spectrum analyser. Then the BU500 would drive the PA and the output from the PA to the 30dB coupler etc.


    Now this is the bit I do not believe of my test gear.



    I offset the display slightly between the two screen saves. The smaller peak is the BU500 direct at just under 2 Watts which is say 32.7 dBm, the vertical divisions are meant to be 10 dB so that puts the upper trace at some 15 dB higher so that would be 47.7dBm or 58 watts. OK it is just a single carrier, but with a input power of 129 Watts it seems high output. No tests done on linearity yet or anything as I have spent enough time on this for today and I would need to sort out cooling fans before I start to push the amps more.

    The plan over the coming days is to test using my Hackrf and MHL21336 Amp to drive it where I can do stepped dB settings, but I need a way to confirm power readings more accurately.


    Suggestions on how I could test them better appreciated?


    Cheers


    Adrian

  • Adrian


    I have had mixed results so far.

    My first amp was modified exactly as per the instructions and this was stable with no input with a quiescent current around 650ma. When driven with 3W the current went up to about 4A and the measured output was 18.6W (plus loss in lead from amp output to 40dB coupler).


    The second amp I modified went unstable when I removed the shunt capacitor at the input and would take more than 5A on switch on with no drive - luckily my PSU has an adjustable current limit and drops the voltage when this is exceeded. I've now put back the cap and taken off the input matching tabs and all is well. Cutting off the output stubs doesn't seem to do much.


    I might try testing the amp at 2320 to see what happens as the output quoted in the notes does not specify the test frequency.


    Barry

  • It's scary seeing 12 Amps draw, I had visions of smoke being released everywhere.


    At present I still have in the input and output circulator's as standard, I read in the notes about the heat-sink being both DC and RF ground for the transistors, and thought the layer of heat-sink compound may be having an effect. I hope it works for you in stopping the instability, as it did for me.


    Adrian


    p.s. I have not tested the un-moddified PA unit so no idea how it would perform. Time to put it away and try to get the odd contact on NB.

  • Hi Barry G8AGN


    If I understand the lime gives 0dBm and spf5189 18dB and 3.7dB attenuation, it would mean that you enter with 14dBm in MHL21336 while it is given in datasheet with max 5dBm input, with 5dBm I have 1W output on 2400 , is this correct ??


    73 F4FDW Laurent

  • F4FDW Hi Laurent, I have a similar setup and the measured gain of an SPF5189 is only 11...12 dB at 2.4 GHz.

    Unfortunately I do not remember the exact input power to my MHL21336, but if I drive it in the linear range, well below 1dB compression, the output is only 1W. Gain is at about 28..29 dB on 2.4GHz. So this confirms your observation.

    Driving the module harder will probably give a bit more output power, but the signal will be distorted. In my opinion 3W in linear mode is not feasible at 2.4GHz. Maybe this works at lower frequencies for which the MHL21336 is specified.

  • Hi DH1DA


    Thank you for the answer, I also think that we must limit the power input on this module but I think you have more than the recommended 5dbm, still to try it.

    Ich werden mal probiren wie weit ich komme mit linear signal

    danke schon

    73 Laurent F4FDW

  • Now it work here.
    Vds = 26 V. IDq=0.7A.
    Pin = 1,2 W (I have not more) , Pout = 17 W, I = 2 A (CW).
    Air cooling radiator 1200cm2.
    Modifyed by SP8XXN and SP5XMU recomendation (tnx Heiner, DD0KP for manual).

  • Im interesting to see your circulator solution.

    Step-by-step:

    1. I removed out the both transistors and the circulator.
    2. PCB, both transistors and circulator was puted in the heatsink (simple flat heatsink).
    3. All fixed with screws. The most difficult job is to mark drill holes and cut threads.
    4. Transistors and circulator soldered into their places on he PCB by slightly bending their leads (they have sufficient margin). This is simple.
    5. PCB modifyed as described in the manual of SP8XXN and SP5XMU.
    6. Unfortunately, PA hav`t PTT. Therefore, a relay was added from the outside of the PA. This PTT relay is switched on +26 V during TX.


  • Step-by-step:

    1. I removed out the both transistors and the circulator.
    2. PCB, both transistors and circulator was puted in the heatsink (simple flat heatsink).
    3. All fixed with screws. The most difficult job is to mark drill holes and cut threads.
    4. Transistors and circulator soldered into their places on he PCB by slightly bending their leads (they have sufficient margin). This is simple.
    5. PCB modifyed as described in the manual of SP8XXN and SP5XMU.
    6. Unfortunately, PA hav`t PTT. Therefore, a relay was added from the outside of the PA. This PTT relay is switched on +26 V during TX.


    Are you using the original circulator? Unsolder and solder is a great idea to eliminate the gap between the pcb and the transistors.