Question on using a MHL-21336 small chip amp.

  • Just checked the datasheet (I use such a module as driver) and indeed .. no reference is given concerning DC coupling, that is . . . sloppy.


    Anyway, in my design (an old UMTS/3G pallet) there are caps (take 56 - 100p or so)

  • G8UGD

    Changed the title of the thread from “Question on using a MH21336 small chip amp.” to “Question on using a MHL-21336 small chip amp.”.
  • G8AGN I saw your response this morning so I set about putting something together as yours was the second one indicated with direct connection. I eventually etched a board, not done that in a long time, I did not follow any rules as I have no software for this just made something up. This is the board mounted on a heat sink.



    I have not put +5 dBm into the unit yet as the Hackrf I have limits at around -2 dBm but it looks like it has 26 or 27 dB gain. So for a first attempt at this in a very long time I am happy.

    Thanks all for your assistance.

  • Your pcb looks fairly similar to mine except that I have a few more grounding screws.

    I included a 6dB attenuator at the input as an insurance policy and am driving the module from a Lime Mini via a SPF5189 board from eBay. The Lime is normally set at 80 or 85% and this seems OK.

    I see you are powering the MHL21336 from a dc dc module; I do likewise and this works well. With about 18v I can get at least 500mw out and 26V will easily give more than 1w. I haven't pushed the MHL as I'm going to use it to drive a SG Labs 20w PA and this only needs about 0.5w for full output.

    Re the discussion about input and output caps. PA3FYM is correct in using caps as the spec sheet doesn't mention whether some are in the MHL module. I haven't used them in my application because the modules on either side of the MHL already contain them.

    The heat sink I'm using at present is just a piece of Ali plate 65 x 100 x 10 mm. This is definitely not enough when the MHL is running at 26V but can cope at 18V.


    If you want more info, pictures, spectrum plots, contact me via pm (see QRZ.com)


    73 Barry

  • Cutting small groves in the track and fitting caps or even a resistor would still be possible. I measured the input current at just over 15 Volts in to the step up unit when transmitting it was 0.96 Amps so the unit is dissipating 15 Watts. I have a small fan I will connect to the fins if I can figure a mounting method.


    I have no larger amps at present, so just hope to get on SSB initially, need to test the POTY next.