MRF300 Amp for 6/4/2m
Posted: Mon Mar 08, 2021 12:16 pm
I've been working on building up amps for these 3 bands using the popular MRF300 RF Mosfet. I found a nice PCB design that uses the PCB tracks as the input and output inductors. The only drawback is it uses 'expensive/hard to get' ATC capacitors to tune the input and output lines (although I don't see why lower spec caps couldn't be used on the input lines).
I bought a pack of 20PCBs from the designer and by various means derived a parts list for the 3 band variants (capacitors in different places/values along the tracks).
I found the required ATC capacitors from a gent in Horsham (UK) for £1.10 each so not too bad.
Just been testing the 50MHz version.
Using the recommended bias didn't produce much RF before the 'shoulders' grew wider, but by tweaking the bias up I can get 30W of clean DVB-T. Slightly less clean at 40 watts so that's about it.
DVBS-2 was more productive - 80 watts clean with -35dB shoulders and 150watts with -25dB shoulders! Harmonic output will need subtracting from these figures.
Now to try the 4m version once its on a heatsink - my current brick amp won't do more than 1 watt of clean DVB-t so I'm hoping for similar results (i.e. 30 not 1!)
.
If you want a pcb (£5 each delivered UK) and the pictures/circuits/lists I've gathered send me a PM.
Gareth
I bought a pack of 20PCBs from the designer and by various means derived a parts list for the 3 band variants (capacitors in different places/values along the tracks).
I found the required ATC capacitors from a gent in Horsham (UK) for £1.10 each so not too bad.
Just been testing the 50MHz version.
Using the recommended bias didn't produce much RF before the 'shoulders' grew wider, but by tweaking the bias up I can get 30W of clean DVB-T. Slightly less clean at 40 watts so that's about it.
DVBS-2 was more productive - 80 watts clean with -35dB shoulders and 150watts with -25dB shoulders! Harmonic output will need subtracting from these figures.
Now to try the 4m version once its on a heatsink - my current brick amp won't do more than 1 watt of clean DVB-t so I'm hoping for similar results (i.e. 30 not 1!)
.
If you want a pcb (£5 each delivered UK) and the pictures/circuits/lists I've gathered send me a PM.
Gareth
- 50MHz_parts_placement.jpg (86.19 KiB) Viewed 1555 times