A Magnetic Core Voltage-to-Frequency Converter

In a Pulse Frequency Modulation (PFM) telemetering system, there is a need for a subcarrier oscillator with these characteristics: 1) operating frequency a linear function of a dc input control voltage, 2) high input impedance, 3) square wave output with constant amplitude over the entire frequency range, and 4) frequency stability within one cycle during gated on-off operation. This paper describes a method for controlling the frequency of a square-loop magnetic core oscillator by means of a dc voltage to give a voltage-to-frequency converter with the above characteristics. Various design considerations are discussed; and a voltage controlled oscillator that operates from 15 to 5 kc as the input control voltage varies from 0 to +5 volts is used as the design example.