1200W HF Linear Amplifier from budget parts - 1

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This is either going to go very well or very badly, and if I'm honest it's 50/50 right now...

I was scrolling through AliExpress (who doesn't?) and I came across a listing for a 1.2KW 1.8-54MHz LDMOS amplifier for a little over $A100.  Of course for this, it doesn't include the BLF188 device ($A300 from DigiKey).

 

Unlike most of the other amp packages on these markets, this one is assembled except for the LDMOS device, so there's no trying to interpret the schematic only to find it has nothing to do with the PCB you have on hand.

 

It didn't take long and the module arrived at my local post office.  It's small, at less than 100mm x 100mm and it appears to be quite well made:


My research also tells me that a multi-band Low Pass Filter is an excellent idea and fortunately the same vendor has a nice unit at about twice the price of the amplifier module.  It arrived in the same package:


 

At about 250mm x 200mm it's substantially bigger than the amplifier, and also appears well made.  If you look closely, you'll see the silk screen says "15KW", but what's an order of magnitude between friends?

So that's the main bits, but it's hardly a complete amplifier is it?  I'm going to need at least the following:

  • BLF188
  • 50V@40A power supply
  • Copper block to mount the MOSFET
  • A big-donkey heatsink and fan(s)
  • A way of switching bands on the LPF
  • A case to put it all in

As for the band switching, my IC7300 has an "ACC" output which indicates the band in use as voltage between 0 and 8V.  If I divide that in half with a simple (but 1%) divider network, I could feed it into an Arduino and use that to control the relays on the LPF.  Given that the LPF runs off 12V I think I will also need opto-isolators.

While I'm there, why not put a current sensor in there as well, Oh and a temperature sensor, LCD to graph it and why not a web server just for fun?

So that's where we're up to at present.  Copper, heatsink and big power supply are on their way.  While I wait for those parts, I am going to start on the control and monitoring module.

Wish me luck!

 




 

Location: Kenthurst NSW 2156, Australia

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