Abstract: A variable frequency voltage controlled oscillator is tuned to a selected frequency by applying a varying voltage to the control port of the oscillator to sweep the oscillator signal through a frequency range which includes the frequency of a reference frequency source. The value of the varying voltage is stored at the instant the oscillator frequency coincides with the frequency of the reference source. A dc offset voltage is then added to the stored voltage to produce a sum voltage which is substituted for the varying voltage at the control port of the oscillator to tune the oscillator to the selected frequency. The offset voltage is equal to the difference in the control voltages at the selected and reference frequencies and may be determined from the oscillator control voltage characteristic.