Ten Minute QRP Transmitter
This is a simple crystal-controlled CW (Continuous Wave) QRP Transmitter circuit designed for amateur radio use, notable for its minimal component count and quick construction time.
The design apparently originated in 1996 in an amateur radio club QRP publication. The name originates since the original author claimed he built this transmitter and make a QSO with it in just 10 minutes time. There are no coils to wind it tunes a wide range of crystal frequencies, and it outputs an easy 500mW AM signal.
Power Supply
- +12V DC supply connects to the positive rail at the top of the circuit
Oscillator Section
- Crystal (XTAL): 3.568 MHz crystal provides frequency stability and determines the transmitting frequency
- Q1 Transistor: Appears to be configured as a crystal oscillator (likely a BFY51 or similar NPN transistor based on the marking)
- Biasing resistors: Two resistors (marked as 0.01) provide proper DC biasing for the transistor – these appear to be current limiting or feedback resistors
RF Output Circuit
- RFC (Radio Frequency Choke): 100μH inductor isolates the DC supply from the RF output while allowing DC current to flow
- Coupling Capacitor: 1000pF capacitor couples the RF signal to the antenna while blocking DC
- Antenna Connection: Output connects to antenna system for signal radiation
Keying Circuit
- KEY: Telegraph key or keying circuit connects between the emitter circuit and ground
- Grounding: Multiple ground symbols show proper RF grounding throughout the circuit
Circuit Operation
When the key is pressed, it completes the circuit allowing current to flow through the transistor. The crystal oscillator generates a stable 3.568 MHz signal, which is amplified by the transistor and coupled through the RFC and capacitor to the antenna. The RFC prevents RF from entering the power supply while the coupling capacitor blocks DC from reaching the antenna.
This is a classic “minimalist” transmitter design emphasizing simplicity and quick construction – hence the “Ten Minute Transmitter” name, suggesting it can be built very quickly with readily available components.
The frequency of 3.568 MHz places this in the 80-meter amateur radio band, making it suitable for CW (Morse code) operation on that band.