Connect the output of the Audio oscillator to the Audio Input socket of the Modulator Circuits block (see Figure 90). Set the Reactance/Varactor switch to the Varactor position. This switch selects the Varactor modulator and also disables the Reactance modulator to prevent any interference between the two circuits. Reduce the Amplitude preset in the Audio Oscillator block to minimum (fully counter-clockwise) Set the Camier Frequency preset in the Varactor Modulator to minimum (fully counter-clockwise).