Crystal-Controlled Shortwave Transmitter

The Crystal-Controlled Shortwave Transmitter is an analog RF circuit designed to generate, modulate, and broadcast a radio frequency signal. At its core, a 4MHz crystal is utilized in conjunction with the IC CD4049, a hex inverter, to form a stable crystal oscillator. The CD4049 acts as both the primary oscillator stage to establish a precise carrier frequency and as a buffer amplifier to isolate the frequency-determining network from subsequent load variations. For modulation, the IC LM386 audio amplifier integrates an audio input signal with the carrier, implementing amplitude modulation (AM) within the system. Discrete transistors like the BC547, along with an arrangement of resistors, capacitors (such as C5), and inductors (L1 and L2), function together to condition the signal, set bias points, and form tuned resonant networks. Finally, the modulated radio frequency energy is fed into an antenna—constructed from a simple wire or window mesh—allowing the circuit to radiate the shortwave signal into free space.