GB1334463A - Frequency measuring circuits - Google Patents

Abstract

1334463 Displaying frequency characteristics SIEMENS AG 13 July 1971 [22 July 1970] 32686/71 Heading G1U [Also in Division G4] A variable frequency oscillator is controlled to generate a frequency sweep and to measure the frequency at a selectable point in the sweep an adjustable voltage representing a desired point is compared with the voltage controlling the oscillator frequency and upon a predetermined condition, e.g. equality, the oscillator frequency is gated to a counter for a predetermined period. In the application shown in Fig.1, the upward and downward frequency sweep of an oscillator 1, controlled by a saw-tooth voltage US from generator 3, is applied to a four-terminal network X whose output after amplification (16) and rectification (17) controls the deflection plates of a CRT 19, with the control voltage US as the time base. Alternatively the four-terminal network output may be digitized in an analyser 25. A voltage U1, representing the point in sweep at which the frequency is required, is compared in a comparator 4 with the control voltage US, and upon equality diving the upward sweep only a timing pulse 5 operates the circuit 6 to generate a pulse 7 of predetermined length which opens gate 8 to feed the oscillator output Uv to a counter 9. The result is displayed, or fed to a store, upon a pulse Uz from circuit 6. Circuit 6 sends either the comparator pulse 5, or a pulse occurring at the centre of pulse 7, to the CRT 19 to produce a mark 24 indicating the instant at which the frequency is measured. Circuit 6, Fig.6 (not shown) includes a further counter which counts clock pulses upon the arrival of pulse 5 until a predetermined count, so defining the gate pulse 7. In a further arrangement, Fig. 4 (not shown) the frequency in the sweep is measured at several points, there being a separate comparator 4 and separate input voltage Ul for each point.