QRP Transmitter for 40m

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
Power, RF spectrum and the transmitter itself
First version of the 40m QRP transmitter

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.

NS40 inspired QRP transmitter
Schematics of the simple 40m QRP transmitter

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.

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