New member - building 13cm amplifier

  • Hi Guys,


    just joined the forum, should have joined a long time ago !

    I'm active on es'Hail and have built local 24cm and 9cm repeaters (GB3FT and FB) - but as you might expect es'Hail is more attractive for any number of reasons and quite a few of the locals are getting ready to operate thru' es'Hail so expect to see more activity from the NW of the UK.

    Anyway I've pulled together all the key parts for a 13cm amplifier using a MRF24300N plus Rogers PCB material, FET, heat sink/spreader etc etc. Another local ham is going to CNC all the parts including the PCB pattern.

    Hopefully it'll all work ok - if it does I have enough Rogers PCB material for about another 15 units.

    The question is should I use the NXP broad band reference design or is there something more appropriate ?

    Currently I'm leaning to copying the the design on page 6 of the NXP data sheet combined with a temp compensated bias circuit.

    Luckily I have a well equipped workshop for test and alignment etc


    Regards Tim G4WIM / KT6UK

  • The board was ready to be populated.. MTL just did the board job. Component assembly and fitting the LDMOS to the heatsink was on me. But ehre are only a few components. Soldering the LDMOS to the copper heatsink was the tricky part (temperature controlled hot plate and measurement of process temperature).

  • Thanks for the info - I had asked MTL to supply / quote but they wouldn't do it without the gerbers.

    So I tried to convert the DXF files to Gerbers but the data was incomplete / in error - I'm hoping the CNC path works out ok as Rogers supplied the substrate as a sample FoC.

    That said maybe Dave and I could combine our orders from MTL if they are able to supply the PCB ?

    I have all the other components / hardware to hand.


    Edit - I'd be willing to fund the purchase of say 10 PCB's if that would make it more viable for MTL to deliver them ?


    73 Tim

  • Hi Dave,


    count me in for one possible three as another couple of locals are looking for some extra power (guess who'll get to build thier PA's ?1)

    As a back up it looks as though the CNC approach is going to work out as the dxf file has been converted and the CNC simulation looks good so now it's just a matter of a couple of test runs before the real thing.


    CNC won't do thru' hole plating though so will have to wrap a bit of copper foil round the edges to provide grounding for the by pass capacitors.


    73 Tim

  • just a quick up date - I now have a number of PCB's for the MRF24300 on the correct rogers material. I had them CNC machined along with the heatsink and spreader are all ready for assembly.

    Plus I've built an 868MHz telemetry / remote control unit to keep an eye on it, It's going to be about 75 mtrs away from the shack.

    I'll post more more pictures later - below was the first attempt and machining the PCB

  • It works - well it shows 16dB of low signal gain at 1Amp quiescent - ie for 15dBm of drive it produces 31dBm output - just testing at low power first will increase drive and use the higher current PSU in the coming days. The heatsink / fan looks small but according to the specs should be ok as the fan moves a lot of air thru it albeit noisily - not a problem as it's be outside anyway.


    Bit of a lash up for a quick test but looks promising.

  • Have now run it up with more drive and capable PSU - an easy 100 watts with Idd of 8 Amps and 200 watts output for about 4 watts of drive. Heatsink is working ok at 0.2C per watt temp rising by 30C above ambient 100 watts output.