Below you see the block diagram for the walkie talkie transmitter.
The carrier oscillator is crystal controlled to guarantee sufficient stability. It is much easier to create a frequency stable carrier by means of a crystal than with an ordinary LC oscillator. The latter would require carefull selection of components and very careful construction to ensure sufficient frequency stability.
The minuscule voice signal from the microphone (a couple of millivolt) is amplified to line level in the audio amplifier. To have sufficient modulation a signal of circa 3- 4 Vtt is required. The bandwidth of the audio amplifier is limited to circa 3.5 kHz.
This is still wide enough for good intelligibility but restricts the used RF bandwidth.
Finally the output is filtered to remove unwanted harmonics.
The oscillator Q1 and modulator Q2.
Recent Comments