Frequency control system for railway wagon counting - monitors frequency of crystal oscillator circuit, connected to VCO output, which receives tuning voltage to set frequency

摘要

The frequency control controls the frequency of a crystal oscillator circuit over a relatively wide range. The crystal oscillator (QO) is connected to one input of a mixer (M1) coupled by another input to the output of a voltage-controlled oscillator (VCO) that receives a tuning voltage to set its frequency. The mixer's output is connected to a filter (HP) that passes only that signal with a frequency from the mixer. The filter is followed by a frequency multiplier (Cg) whose output is connected to the input of another mixer (M2) that mixes it with the output of a sweep oscillator (WO).