This is a Class E Transmitter designed for the 40-meter amateur radio band, capable of producing approximately 4.6W output power at 80% efficiency.
Class E Transmitter
Power Supply
- 11.5V DC supply (Vcc) powers the circuit
- 470µF electrolytic capacitor provides power supply filtering and decoupling
Input Stage
- 1M input resistor provides high impedance input matching
- 10µH RF choke isolates the input from DC while allowing RF to pass
- 39pF capacitor couples the RF input signal
- 22nF bypass capacitor provides RF grounding for the bias circuit
Driver/Buffer Stage
- 2N700 transistor (Q1) acts as a driver/buffer stage
- 1µH inductor in the collector circuit provides RF choke function
- 10µF capacitor provides DC blocking and AC coupling
Class E Power Amplifier
- SK3570 transistor (main power device) configured as a Class E amplifier
- 22nF capacitor in the base circuit provides RF coupling
- 100nF capacitor serves as the Class E shunt capacitor across the transistor
- 220Ω resistor provides base bias/drive limiting
Output Network
- 71nH inductor (L1) forms part of the Class E load network
- 100nF and 1000pF capacitors create the output matching and filtering network
- The output network is designed to present the proper load impedance for Class E operation while filtering harmonics
Class E Operation Principles
Class E amplifiers operate by switching the transistor fully on and off, with careful timing so that voltage and current don’t overlap significantly, resulting in high efficiency (80% as noted). The LC network ensures the transistor switches when voltage across it is minimal.
Performance Specifications
- Output Power: ~4.6W
- Efficiency: 80%
- Operating Voltage: 11.5V
- Operating Current: 0.5A
- Frequency: 40m band (approximately 7 MHz)
The circuit demonstrates excellent engineering for a compact, efficient transmitter suitable for portable or QRP operation on the 40-meter amateur band.
Build Your Own Commando AM Transmitter