Hans G0UPL who operates QRP-Labs has released his 10W HF Linear Power Amplifier. This kit comfortably produces 10W from a 12V supply. It is a compact design with huge heatsink included, which will not overheat even on continuous 100% duty-cycle operation. The amp provides 26dB gain with +/- 1dB gain flatness from 2 to 30MHz.
This 10W HF Linear Power Amplifier kit has no Surface Mount Components (SMD) to solder. There are a number of small transformers to be wound, and assembly requires care and patience.
The push-pull driver stage uses two BS170 transistors in the amplifier design used in the SoftRock transmitter stage. The final uses two IRF510 transistors in push-pull. Yes, this humble low-cost MOSFET really is capable of excellent performance all the way up to 10m band and beyond! Short lead-lengths and PCB layout are extremely important, they are the key to success.
- 10W output from 2 to 30MHz, using 12V Supply
- Generously-sized heatsink, will not overheat even on continuous 100% duty-cycle modes
- 2-stage amplifier provides 26dB of gain
- Push-pull driver and push-pull finals, for high linearity and low harmonic content
- +/- 1dB gain flatness from 2 to 30MHz
- 4dB down at 6m (50MHz) and 8dB down on 4m (70MHz)
- Standard 50-ohm input and output
- Through-hole plated PCB, all through-hole components (no Surface Mount Devices)
- Standard inexpensive components throughout
- Tested for 1 hour at full-power 10W, 100% continuous duty-cycle with no forced air cooling
- Tested for 15 minutes at 20W, 100% continuous duty-cycle with no forced air cooling
- Tested at 20V supply
- Tested into open load, shorted load and various mismatches without instability (oscillation)
As Hans advises on the BITX20 I/O Groups list:
I am not suggesting that this amplifier will solve all problems and without wishing to be offensive, the “garbage in, garbage out” rule always applies – in particular, if you feed it a signal containing spurs, harmonics, or other problems… then you will get the same thing at the other end, just amplified 26dB. It also still applies that all stages leading up to the final amplifier must have flat gain. If the pre-drivers cannot provide a big enough signal then you won’t get full power output.
But, it could be useful or interesting, in the BITX context, to look at the details of this amplifier kit and see the short lead lengths, symmetric PCB and extensively “stitched” groundplanes.
For further information see the product on Hans website.