Abstract: Tires of vehicles can be accurately tested by providing a voltage controlled oscillator for generating output signals substantially free of jitter. Digital up/down counters responsive to data signals and the output signals generate a counter signal which increases or decreases depending on the relative frequency between the data signals and output signals. A conditioning circuit, including a digital to analog converter and an integrator, is connected between the counters and the signal generator so that the signal generator produces an output signal which tracks the data signal in frequency and so that an output signal is produced for every data signal over a wide range of frequencies.