Last Weekend I found some hours to start a little QRP transmitter project. For the Minimal Art Contest in 2015 I want to use a homebrew transmitter with less than 20 parts and 5 Watts output. I used the design from the Four States QRP Group as starting point and modified the output network. The first result looks already promising:
- more than 8 Watts Output at 12 Volts supply
- 38 db Suppression of 2nd harmonics
I started with the following schematics and parts for 40m with a modified output network. The output network was calculated by using a spreadsheet for class E power amplifier design according to NM0S equations presented at FDIM 2009.
When keyed the transmitter, I could only measure about 2 Watts output instead of the expected 5 Watts. After removing C4 and C5 and reducing C3 to 1nF the output increased to more than 8 Watts. Now I need to start some simulations in order to understand the observed results.