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Schematic
The voice is detected by an electret microphone , then it comes amplified and filtered by U1 pass-band in order then to be presented at the carrier section, where through the varicap diode it "mixes" with the frequency generated by the quartz, that guarantees an adapted stability. Practically the modulating tension is obtained applying the audio signal to the diode valve varicap of the resounding circuit that determines the carrier oscillation. The carrier frequency (160 MHz) must be greater than the modulation frequency (300-3300 Hz) audio band.
The transmission will happen on the harmonic quarter, therefore 160MHz, the oscillation frequency of the final transistor RF Q1.
A small calibration is allowed acting on the L1 inductance and the C1 Trimmer Capacitor.
Who wants to elaborate on the overtone modality can leave a comment...