Patent ID: 7747403

Claim:
A measuring device, comprising: a plurality of intermediate-frequency superposition stages, a variable-frequency first oscillator for a first one of the superposition stages, a first mixer of the first superposition stage, an analog/digital converter, a signal processor for evaluating an input signal according to a Fast Fourier Transform principle, a supplementary mixer, and at least one of: a frequency divider disposed between a first input of the supplementary mixer and the variable-frequency first oscillator, and a frequency multiplier disposed between the input of the measuring device and a second input of the supplementary mixer, wherein, in a spectrum analyzing operating mode for analyzing a frequency spectrum of the input signal, the input signal is converted by the variable-frequency first oscillator, the first mixer and each of the superposition stages subsequent to the first superposition stage into a plurality of intermediate frequencies, digitized in the analog/digital converter and evaluated in the signal processor according to the Fast Fourier Transform principle; and in a phase jitter measuring operating mode for measuring a phase jitter of the input signal, the input signal is selectively multiplied in the frequency multiplier, and then mixed down to a frequency zero in the supplementary mixer with an output of the variable-frequency first oscillator that is selectively divided in the frequency divider, the variable-frequency first oscillator is controlled via a control circuit in such a manner that frequencies of signals supplied via the first and second inputs to the supplementary mixer are identical, and an output of the supplementary mixer is then supplied directly to the input of the analog/digital converter and evaluated in the signal processor according to the Fast Fourier transform principle thereby measuring the phase-jitter of the input signal.