Simple Shortwave Voice Transmitter

The Simple Shortwave Voice Transmitter operates by combining an audio input stage with an RF oscillator and a power amplification stage. The circuit begins with the microphone (MIC1), which converts acoustic voice waves into weak electrical audio signals. This audio signal is coupled into the LM386 audio amplifier IC (IC1), which boosts the signal level to provide sufficient drive for modulation. Meanwhile, the crystal (XTAL1, such as 7.2MHz) establishes a precise, stable radio frequency carrier wave. The amplified audio modulates this carrier using the 2N2219 transistor (T1), which acts as the core oscillator and modulator stage. The resulting modulated radio frequency signal is then passed to the BD139 transistor (T2), serving as a power output stage to increase the signal strength before transmission. Throughout the circuit, RF chokes (RFC1, RFC2, RFC3) are strategically placed to isolate the RF signals from the power supply rails and prevent unwanted feedback or leakage. Capacitors and resistors are used for DC blocking, biasing, and tuning across the stages. Finally, the modulated RF output is fed into a short-wire antenna, radiating the voice signals over the lower shortwave band.