Sometimes we all need a bit of QRO - Life's too short for QRP sometimes. So we give you the Baby-QRO switching amplifier!
This Baby-QRO switching RF amplifier design is inspired by the wonderful Single NXP MRF-101 Eval Board project by Jim Veatch. Thank you Jim!
Instead of using the expensive MRF101 MOSFET, we use fast SiC MOSFET(s) from Wolfspeed / SUPSiC.
3D render:
Schematic:
This PCB was tested in late January-2025 and it works great. It produces 100W+ at 50V drain on 7 MHz. The gain drops with increasing frequency but not too badly!
Results:
| Settings | 7 MHz | 14 MHz | 28 MHz |
|---|---|---|---|
| 9V driver, 43V drain | ~70W | ~60W | 30W |
| 12V driver, 43V drain | ~70W | - | - |
| 12V driver, 48V drain | 100W | - | 60W |
Efficiency (of the final MOSFET) is close to 50% on 28 MHz and around 55% at 7 MHz.
The input RF comes directly from the Si5351 (3.3V). You can use our CW-SigGen project to generate a suitable test signal. It is also possible to pair this amplifier with our Easy-Digital-Beacons-v1 project.
Another motivating factor: MRF101 is 'too precious' (read expensive) especially with its thermally self-limiting TO-220 package.
Cost for 100W: Around 15 dollars - for everything including PCB and BOM components
Time to build: Less than 30 minutes - no coils to wind - yay!
The files for this project are published here for personal (non-commercial) usage.