Wireless am microphone Transistor Ql and its associated components comprise a tuneable rf oscillator. The rf signal is fed to transistor Q2, the modulator. Operational amplifier ICl increases the audio signal and applies it through resistor R4 to the base of Q2. Tune an Wireless am microphone AM radio to an unused frequency between 800 to 1600 kHz. Tune Ll for a change in the audio level coming from the radio. Peak the output by adjusting L2 If Ll is disturbed, it may be necessary to readjust L2 for peak performance. Depending on the impedance of the microphone audio sensitivity can be increased by decreasing the value of RIO and vice versa. Wireless am microphone.