Let's build a PA for 2,4 GHz

  • Thanks Dave appreciate the good words, I do indeed key the bias via the PTT. Overall I’m a bit further down the line with the Spectrian now. Have applied the VK4OE ’snowflake’ which has taken it to 30W. Added a decent fan and using the embedded sensor (duly converted to Celsius) wrapped it with a PID loop to modulate the fan PWM. Also added an option for USB PTT. The amplifier now plays nicely with the LimeSDR mini and SDR Console.

  • The bias level is a compromise between efficiency and linearity. Need to find the sweet spot.

  • For SSB Class AB is quite sufficient. No need for nearly Class A.

    I agree but that is not an answer that is universal. SSB is not the only mode being used via OQ-100 so it depends. If you are doing DATV, which is where you need the larger powers this amplifier can generate, you might need more bias, or not, there is a sweet spot between current and spectral regrowth.

  • I agree but that is not an answer that is universal. SSB is not the only mode being used via OQ-100 so it depends. If you are doing DATV, which is where you need the larger powers this amplifier can generate, you might need more bias, or not, there is a sweet spot between current and spectral regrowth.

    I specified SSB so it is correct. Please don't nick pick !

    Dave Cawley | Ex G8EAO & G6ANG/T |
    (when you had to have a separate TV license !)

  • I have actually left the bias 'as is' because I do want to try the DATV transponder at some stage. Just about got the setup as I want it now but I'm sure that won't last for too long!

  • as promised I give you an overview on the progress for building a low cost PA for es'hail-2 NB transponder.


    We have the prototype finished and tested. It is running fine.


    The total cost of material of the amplifier is about 20 Eur only.


    The performance data are:


    at 12V/850mA

    output power is 5 watts

    with 100mW input (nice fit to the Amsat TX mixer board)


    at 24V/680mA

    output power is 10 watts
    with 200mW at the input.


    You can read more detailed information here:


    English:

    https://www.helitron.de/dj0abr…sh/technik/sat/sat_pa.htm


    German:

    https://www.helitron.de/dj0abr/german/technik/sat/sat_pa.htm


    since this prototype works so well, we will continue with a second version including a PTT circiut and a few other parts. But we keep it simple so everybody can build it easily.


    If more gain is required (i.e. for SDR transmitter), simply two of these boards can be chained, giving a total gain of up to 34 dB. I have used two boards in series for the power tests because my generator has only 10mW max output.


    All parts are available worldwide from digikey or mouser.

    I have 4 PCBs left, if anyone wants to build it, just write me a forum-message.


    The part list, circuit and gerber data will be published on above web pages during the next days.


    vy 73
    Kurt, DJ0ABR


  • Congratulations Kurt.

    Last month i tested two PA without sucess ( Counterfeit parts and re tuning 2100 mhz LDMOS) . I will try to buy MHT1008N for test.



    73 !

    PY1SAN

    Sandro

  • just did the first QSO with this PA with DK1KQ. He reported a good signal.

    120cm dish and the homemade dual band patch feed (according the NL and G document).

    The previous measurements were taken with a continuous carrier from a signal generator.


    In SSB the power is maybe half of that because we need linearity. With 24V and the Amsat board as the driver (abt. 50mW, maybe up to 100mW) the SSB output power was about 3 watts. This made an average signal on the NB transponder like most other stations are doing.


    The current board was just made to prove the concept. For a real PA a few things are missing, like a PTT circuit to switch on the quiescent current during TX only. Also I want to change the size of the board so it fits into the usual Tin cases.


    I will publish the PCB data this evening, mainly for people doing tests and measurements. If you want to use it for regular sat operation you should better wait for the next layout which is hopefully available in 10 days from now.


    Also, FR4 is not FR4, if a board is made from a different manufacturer, it may be required to check the input match.


    vy 73
    Kurt, DJ0ABR (DC1RJJ)