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.
Design
3D render:
Actual picture:
Schematic:
Results
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!
| 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.
Note: For 100% duty digital modes, derate the power by 1/2 or even 1/4 for ensuring device longevity.
Note 2: The Würth Elektronik coupled inductor can get hot beyond 100W levels - folks have used T200-2 based transformer successfully at higher power levels.
Note 3: If you are interested in lower bands only (160m to 40m) then you can choose a more beefier (but slower) SiC FET / Silicon MOSFET part. Data point: The UCC27517 gate driver is good enough to drive the slow IRFP150N MOSFET directly to about 16 MHz or so. Using GC3M0120090D SiC should be able to produce higher RF output at higher drain voltages.
Excerpts:
SiC params:
MOSFET params:
Usage
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
Cost for 100W: Around 15 dollars - for everything including PCB and BOM components
Time to build
Time to build: Less than 30 minutes - no coils to wind - yay!
Files
The files for this project are published here for personal (non-commercial) usage.
Success Stories
A bunch of Finnish HAMs have reproduced and validated this design - thank you!