Abstract: A signal generating device and method of control thereof for producing a desired output frequency, the generator having coarse and fine tuning controls capable of producing frequency changes over a limited range, wherein the output of the device is combined in a mixing device with a multi-component reference signal produced from an oscillatory generator circuit, a beat signal is detected by processing circuitry as the frequency controls are adjusted and the values of the frequencies of the control signals occurring on such detection are stored, and using a look-up table or algorithm the value of a correction signal is determined which, when combined with the stored values, will cause the output frequency of the device to be adjusted to the desired value via the fine tuner.