Frequency dependent steepness measuring circuit - for modulators or demodulators creates measuring conditions without modulator quality knowledge

摘要

The frequency modulator (27) is modulated with a wobble-frequency voltage and supplies a phase modulator (28) whose reference voltage is produced by a comparison oscillator (30) whose frequency and phase depend on the mean value of phase modulator output voltage. The oscillator frequency is equal to the carrier frequency of the f.m. signal and has a constant mean phase difference with the latter. The hyperbolic relationship between the phase modulator output voltage amplitude and the modulation voltage amplitude at the frequency modulator input arising when the frequency modulator and the phase modulator are connected in series with each other is compensated by a correcting element with a frequency strictly proportional to that of the modulation voltage.