Posts by G8AGN

    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

    Heiner


    I've have just checked out one of the "new and unused ?" unmodified Bison PA boards, as you suggested.

    The test setup - see photo - is a Portsdown RPi3 giving a H265 QPSK S2 signal 125kS/s which drives a Lime SDR Mini. This then drives a SPF5189Z board from eBay and then a homebrew MHL21336 amplifier which gives just over 3W at 2.4GHz. This is then fed directly into the PA board.

    The measurement setup is a 40dB coupler terminated by a Bird 50W coaxial load. Power is measured using a HP437B power meter.

    Results were:

    Lime Mini gain = 95, output = 12.2dBW = 16.6W

    Lime Mini gain = 100, output = 12.7dBW = 18.6W

    The output will be slightly higher because of the loss in the cable between the PA and the coupler.

    These figures compare very well with those quoted in the modification notes you sent me earlier.

    73

    Barry

    I've just tried out my PA but results are disappointing so far, only just over 20 watts (28V, 3.5A) with about 3 watts drive from a MHL21336 chip. This is being driven by a Lime Mini DATV signal which feeds into a SPF5189Z. Originally I had a 6dB attenuator between the SPF5189Z and the MHL21336 but I have now reduced this to about 3.7dB.

    I have made the modifications to the PA board as described in the notes from Heiner and used 5mm copper tape as mentioned in previous posts. This seems to work well and is easy to do.


    The PA board is identical to the ones shown in the notes but came from another supplier on eBay. I also have two of the ones from Bison which I'm keeping "in reserve" while I learn from playing with the single board.


    The notes mention that more output power can be obtained by not using the input and output isolators on the PA board. Does anyone know how much loss these components may have at 2.4GHz?

    The input circuit on the board has two components to be removed. One is an isolator (labelled X2) but I do not know what the ceramic component near it is - any suggestions please?


    73 Barry, G8AGN

    Adrian


    Yes, my PA boards came with short leads with a crimped P SMP plug at each end - the coax is flexible not UT141 semi-rigid. The Digi-Key plugs are meant for 141 semi-rigid.


    Re your milling of the heat sink, note that the 28v power connectors on the PA pcb each have two plastic (locating ?) bumps which protrude on the ground side. I just snipped mine flush with some side-cutters.


    Barry

    P SMP connectors to fit the PA boards can be found at Digi-Key


    Right Angle Jack (Jack Female Socket 50 ohms) Digi-Key part no 1868-1052-ND (Rosenberger 119K207-272N5)


    Straight Jack (Jack Female Socket 50 ohms) Digi-Key part no 1868-1045-ND (Rosenberger 119K101-272N5)


    These are available as 1 offs at about £9 each +VAT + postage.

    Both connectors are solder type for UT-141 cable


    73 Barry


    Instead of milling recesses in the heatsink for the transistors and isolator, I am going to use a spacer plate made of thin brass sheet which has rectangular holes for the transistor heat sinks to pass through. These holes can be cut by hand, so no milling machine is needed. So the transistor heatsinks will be bolted directly to the main heat sink.

    In my case I found that the spacer plate needs a thickness of about 0.5 mm and brass sheet of this thickness is found in model shops (in the UK) . It is branded K&S # 252 and a sheet 0.016" x 4" x 10" (enough for two PA boards) costs about £6.

    73 Barry G8AGN

    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

    I am still unable to get DVBS-2 demod_gui working with my SDRPlay RSP2. Exactly which files do I need to download from the SDRPlay website and in which folder do I install them please? I can get the software to run with my Lime-mini.


    73 Barry