This circuit allows for FM modulation in the aforementioned wireless microphone or radio. Here, a back-to-back varactor configuration minimizes the effects of RF modulation.

The output level of the modulator is -5 dBm. In this fm modulator prototype the varactor bias was 7.5V for the best linearity but this could be different with other varactors.

In contrastm the transmitter schematic we present here eliminates some of those problems, using varactor diode for tuning and modulation, givind great sensitivity without an audio amplifier. FM ...

One analog technique is to directly modulate the VCO. A common arrangement is to use varactor diodes (voltage-variable capacitors) to change the capacitance value in the VCO LC tuned circuit.