The above 7 Mhz 5 Watts CW Transmitter circuit was found in one of back issues of sprat. Still i am wondering how 5 watts juiced out from this tiny crystal oscillator circuit.
This classic 7 MHz CW Transmitter circuit demonstrates how effective amateur radio equipment can be built with minimal components and straightforward design principles. Operating on the popular 40-meter band, this single-transistor transmitter delivers a solid 5 watts of CW output power, making it an excellent choice for portable operations and QRP enthusiasts.
The heart of the circuit centers around a 2N3053 transistor configured as a crystal-controlled oscillator and power amplifier. The 7 MHz crystal ensures frequency stability, while the transistor simultaneously generates and amplifies the RF signal. The output tank circuit, consisting of the 45-turn inductor wound on a 3/8-inch form and the variable capacitor, provides impedance matching and harmonic filtering essential for clean signal transmission.
What makes this design particularly appealing is its simplicity and reliability. The metering circuit allows real-time monitoring of output power, while the straightforward keying arrangement ensures clean CW operation without clicks or chirps. The modest 9-12 volt power requirement makes this transmitter ideal for battery operation during field days, camping trips, or emergency situations.
The inductor specification of 45 turns using 26 AWG wire on a 3/8-inch form provides the correct inductance for 40-meter operation, while the output coupling network ensures efficient power transfer to a 50-ohm antenna system. This proven circuit topology has been successfully replicated by countless amateur radio operators, making it an excellent starting point for anyone interested in homebrew QRP equipment construction.
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To my self i real like to explore RF circuits