What TX amplifier do you plan to use?

  • the time was ok, but i Txed on 630.


    @PA3FYM:

    regarding the description to build your dualband patch antenna:


    There should be a note "not" to use N-connectors.

    If the feed is aligned in the focus, then the N-plug is almost in the same place as the LNB holder of a standard dish. No chance to screw on the cable connector. With SMA it is no problem.

    For non-standard dishes or home made LNB-holders it may work also with N-connectors.

  • Claudio, if you talk about the 75W spectrian PA, just an approximate calculation:


    It is specified for 75W output at 26V / 17A DC input.

    The power loss (to be cooled) is 26*17 - 75 = 367 watts.


    If you have an ambient temperature (in Italy) of i.e. 30 degC, and you allow the amp to get a max. of 60 degC, then you have a temp difference of 30 degC.


    The cooler you need should have 30 / 367 = 0,08 K / watt.


    A cooler with a thermal resistance of 0,08 K/W is a real big one. You will usually need one or more cooling fans to achive that value. Or if you have enough space you can do passive cooling.


    As an example of a cooler without fan:

    cooler-1


    or with fan:

    cooler-2


    if you choose the maximum cooler temperature, please take into account that the chip (the chip inside the transistor) gets hotter then the cooler. To do an exact calculation you need to check the datasheet for the thermal resistance of the transistor, the mounting ... This is sometimes difficult to calculate, so a good reserve is needed.


    73 de Kurt

  • Kurt


    Nice description!


    I agree it is generally not possible to reverse calculate the thermal resistance from chip to outside casing of an amplifier. It is hard to do accurately even as the designer of the amplifier. I would guess that for a professionally built amplifier, unless you have the manufacturer's spec to hand, then 60C maximum baseplate temperature is a good figure to aim at.


    I have also used water cooling of SSPAs with great success. It is not too difficult - a copper block with copper pipe soldered to it and a bucket of water and fish tank pump works pretty well, but I have not measured the thermal resistance of this.


    73


    Charlie

  • ....

    I have also used water cooling of SSPAs with great success. ...

    I am also a great fan of watercooling. Did it for my SW 1kW amp and it works very well.

    In this case I have the problem that the 13cm PA is mounted at the dish which makes it hard to install a water cooling, but it would be nice to have :-)

    (just discovered that the status of my upconverter-order in the Amsat shop changed from waiting to finished. This makes me very happy, I'm looking forward to the first QO100 qso).

  • It is not so EH2 related but i also own a water cooled amplifier.


    Its from an old Coherent DEOS Lasersystem, delivers easily 1,2KW on VHF.


    Supply voltage is 48V so not usable as "portable" amp, not to forget the needed chiller.


    1K2 looks much on VHF but compared to the bigger Laser RFPSUs (E1000) with >10KW at my QRL this is a tiny amp ;)


    I only fired it up once on a dummy load, because neither my coaxcable or antenna can handle this much power.


    Vy73s DB8TF

  • Claudio,

    Heiner's link shows a very good paste.


    You should set a reasonable quiescent current. There are some descriptions in the net talking about 2A per mosfet. This is too high and results in a very hot board needing a huge heat sink.


    I am using 0,6A per mosfet (1,8A in total), linearity and gain is ok, and higher current only slightly improves that.

    If the +12v- enable pin is connected to the PTT (via a relais), then you can use it for normal SSB with a little cooler in the size of the spectrian board.

    This may be different for long transmissions like sstv, but I have not tested that until now.


    73 Kurt

  • I modified my Andrew PA with MRF21045 wich was originally matched for UMTS with som SMD capacitors. Now I got 13dB gain on 2.4GHz and 20W output with 0.5W input from my modified TQP7M9103 amp (see also 1W Amplifier in this forum). Pupply Voltage is 28V.

  • I received the PA now from Bison Electronics poland.


    This amp is a doherty type, so the second final amp gets only IDq if the first amp is near to saturation. I think for linear use on 2,4GHz it is better to have both final amps idled equally. The modification is removing two resistors and adding a connection.

    See in the attached picture. I also post the power connection pinout.

    To make things easy the whole IDq circuits are directly powered by the 28VDC.

    The IDq (without the PreDriver) is about 3,1A@28V.

    I expect about 100W Pout from that SSPA on 2,4GHz.

    When i have powered up the SSPA i will post where the directional coupler output pins are.


    VY73 de DB8TF

  • DB8TF Did you find a datasheet for the BLD6G22L- 150BN/2?


    I could only find the data sheet for the BLD6G22L- 50. which isn't much help for finding the required bias current unless you assume the -150N/2 is 3 or 4 -50's in one package. Also if you put both parts of the chip into class AB will you have to de rate the chip to cope with the lower efficiency?


    Also I noticed from your screenshot you had removed two devices on the input? I presume they were filters of some kind?


    The board looks good value for money since it comes with a top case and a heatsink - I'm just worried about getting one where the doherty bit is built into the chip with no datasheet


    Richard

    +

  • Hello


    thanks for your description, I also ordered one. How did you solder the SAW filters and the other things out? Next up someone wrote that it is hard to solder because the base plate absorbs the heat strongly. Maybe OH3WE writes us how far he is
    with the PA.


    73 Klaus

  • M0VKK : i dont have a datasheet but i can tell you that the factory set IDq is 1.34A per final amp.


    DH1KP : the small preamp and the small filter as also the circulator could be removed with a stronger soldering iron (i used 80w@450°). The bigger filter can be carefully dismantled and then you can directly heat the base of the filter till it comes off. remove the pcb from the heatsink to unsolder those filters!


    vy73 DB8TF