Looking to experiment with amateur radio on the 40-metre band? This Simple 40 Metre CW TransmitterUsing 2N2222 is a great DIY project for beginners and QRP (low power) enthusiasts. Designed around the popular 2N2222 NPN transistor, this transmitter operates on approximately 7 MHz, covering the popular 40m amateur radio band.
This transmitter is designed for low-power (QRP) operation in the 7 MHz amateur band (40 metres). It uses a crystal oscillator for frequency stability and includes an output filter to ensure clean RF output.
The 40 Metre CW Transmitter circuit consists of the following functional blocks:
1. Crystal Oscillator (7 MHz)
At the heart of the transmitter is a 7 MHz crystal oscillator, which sets the operating frequency precisely. This crystal controls the base of the 2N2222 transistor in a simple oscillator configuration, ensuring stable, drift-free CW operation.
2. Keying Circuit
A manual Morse key is placed between the transistor emitter and ground. When the key is pressed, the oscillator is activated, allowing current to flow and RF to be generated. When released, the transmission stops — allowing on/off keying (CW transmission).
3. Output Stage
The RF signal generated at the transistor’s collector is coupled through a 0.01 μF capacitor to the output network. The collector is loaded with a low-pass filter built using a 12-turn T-50-2 toroidal inductor and three 330 pF capacitors. This filter removes unwanted harmonic frequencies and ensures a cleaner signal is delivered to the antenna.
✅ Why This Circuit is Great for Beginners
- Minimal components
- Stable frequency thanks to the crystal
- Teaches basics of RF filtering and transistor oscillators
- Easily built on perfboard or with Manhattan-style construction
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