Let's build a PA for 2,4 GHz

  • it looks like the German (and EU) customs is selecting out the Chinese Wlan Amplifiers. It gets more and more complicated to get it . Two of my orders never arrived and aliexpress dealers do not ship into the EU any more.
    Whats still available on ebay is usually fake.

    Do we need the Chinese ? No, we can do that by our own, and we can do better !

    What about concentrating our knowledge to build our own QO-100 amplifier ? I cannot do it alone, but if we work together, we can succeed.

    What I can do: PCB Layout, purchasing parts, manufacturing the prototypes

    what is needed: experience designing 2,4 GHz circuits, calculating 2,4 GHz strip lines, designing snow flakes and similar. And we need someone with test equipment for 2,4 GHz who is able to test the prototypes (my instruments end at 1 GHz).

    Some suggestions as a starting point:

    available at Mouser and Digikey: the freescale MHT1008N


    18,5dB gain and 12,5W max CW power. Would be a perfect match to the Amsat TX converter.

    We could start with building the reference design from the data sheet, unless somebody has a better idea.

    Using a Rogers PCB material the total cost of material could be < 50.- Eur (in qty of 20 or more).

    I am not interested in any profit. If such a project generates a little profit we could give it to Amsat for their excellent QO-100.

    So, thats my idea.
    What do you think about it ?

    vy 73

  • Hi Kurt,

    You are running behind the market. Pick your choice from already available solutions:

    F6BVA - 20W with MW7IC2725N, DIY project

    SG Lab - 20W with PA2400, readily built

    Rene PE1CMO - 20W with BLM2425, readily built

    Further options are: the 30W Spectrian driver board readily built with small mod to do, the Andrew MRF21045 modules with15-20W (with mod to do) and several other UMTS boards.

    For sure there will be more designs applicable.

    73 de Cor

  • nice comments !

    Now we have a good list of available options.

    I have the Spectrian here which I will activate the next days, so there is no real need for a PA here, but I will do something this summer, just for fun. Building equipment is a great hobby.

    Heiner, mny thanks for my first QSO on QO-100, running 0,4 W only.

  • Hi All, Following this with interest and would like to add a few thoughts...

    Currently I use the 30W Spectrian module which is probably not much more than 20W at 2.4Ghz. Due to its class A operation it spends most of it's life keeping the shack warm so I am considering a replacement in due course. Whilst I am an avid constructor my test equipment presently tops out at 1.5GHz and being an LF guy by profession I'm afraid I don't have the skills to design a 13cm amplifier board from grassroots. So I am pleased to see this discussion develop.

    I agree with the comments that the SG Labs amplifier looks excellent value for money and as it stands it seems hard to beat for overall value once you factor in the cost of a nice enclosure. The amplifiers mentioned earlier in this thread would be great for the Amsat-DL up-converter and transverters with outputs in excess of 25dBm. I think though that there is a bit of a market gap for an amplifier designed to be driven by small SDRs like the Pluto, LimeSDR or HackRF all of which really need some decent 2.4GHz filtering on their outputs, ideally bandpass but at least lowpass as they are by design wideband devices.

    I currently use a SAW filter and Gali-84+ combination in front of the Spectrian as the LimeSDR mini only delivers circa 0dBm at 2.4GHz. I have yet to see any of the Chinese preamplifier modules that many people use to boost SDR output with any bandpass or lowpass filters as they are mostly designed to be broadband. The exception being the rather expensive Analog Devices CN0417 2.4GHz evaluation board that I see some are using which does have an input bandpass filter which is ideal but costly. Whilst modern LDMOS devices such as the MW7IC2725N have on board matching and tailored response is still better to drive them with a clean signal.

    So I feel there is a need for a 0dbM input level amplifier with filtering for SDR drive and possibly also for a pre-amplifier type board with some front end filtering for existing power amplifiers. After starting with a mini-kits transverter I'm now rebuilding my Spectrian amplifier enclosure to contain the filtered pre-amp (I'm using a Murata SF2124E with Gali-84+) and USB PTT switching that I use with SDR Console and the limeSDR mini as I personally prefer the SDR route.

    I'm also looking forward to the LimeRFE :- https://www.crowdsupply.com/lime-micro/limerfe

    73 de Clive, G4KCM

  • Hello everybody,

    for the SDR users like me there is currently nothing complete to buy. There are various solutions to get to the 0.5W for a SG Lab - 20W amplifier.

    Also, it is not clear how long it takes until the LimeRFE is available and if you also need the rest of the functions because you only work with the SDR via Sat.

    For me it is only time to search and test together because I want to use the LimeSDR

    73 Markus

  • the SF2124E looks good. Is there a stock somewhere in EU ?

    for a pre-amp 0dBm input and 27dB gain there are many devices available,

    just as an example the SE2576L-R from Skywork Solutions, which has already an integrated input match. and needs 5v at abount 0,5amps.

  • For the Spectrian driver board owners in this thread pointing to low output level, please note this rather simple mod to achieve over 30W at 2.4GHz.

    It comes from a message by VK4OE (remember the Aussies do use 2.4 as their normalcommunications band). Here a copy of the message:

    Hello Colin and other readers.

    I feel that I can't assist your problem any more than the help you've already received. But I wanted to add that I do have one of these amplifiers working perfectly well at 2403 MHz, the centre of amateur activity here in VK.

    However, I did go through the whole amplifier chain trying to find locations for solderable tabs ("snow flaking"), hoping to make it work better at this further-out-of-band frequency. The interesting thing is that I did find one sensitive/responsive point and it was between the final device and the output port, where the microstrip track takes a left hand turn - see attached 'image.

    At 2403 MHz, 10 mW input delivered 31 Watts output following this small addition.

    It was also interesting that there seems to be a layer of some plastic material everywhere which has to be melted away before the solder will 'take' - it makes the resulting soldered joint less than good looking!

    I wish you well with rising to your challenge!

    --Doug Friend, VK4OE.


    73 de Cor

  • thanks to all answering my request for building a low-cost PA for QO-100.

    We now have a small group of hams, and also access to R&S test equipment.

    We started the development beginning this week.

    Circuit and layout is ready, components arrived.

    Next week, when we get the PCB, we start assembling the prototype and testing.

    Designing the matching using PCB-traces was not easy, so there is a high risk that it maybe will not work as expected and we have to make some changes in the layout. We will see. If it works I will publish all documents to the community.

    More information end of next week.

    vy 73, Kurt, DJ0ABR

  • Quote from G4KCM

    Currently I use the 30W Spectrian module which is probably not much more than 20W at 2.4Ghz.


    Mine is 26W out of the box. Just turn down the bias on PA and driver and it runs much cooler. Also only command it on when transmitting.

    Simples !


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