Frequency-selective calibrated amplitude-measuring system

Claim 1

A circuit arrangement for giving a calibrated amplitude reading of an alternating signal voltage of selected frequency, comprising: a first oscillator generating a fixed reference frequency fo; a second oscillator generating a widely variable test frequency ft1 a source of at most limitedly variable ancillary frequency fc; additive mixer means and subtractive mixer means connected in cascade; switch means having a measuring position for applying to a first one of said mixer means said test frequency ft and an input frequency fe of an incoming signal voltage, thereby generating a first beat frequency fi1 fe + OR - ft upon saiD test frequency ft bearing a predetermined relationship with said input frequency fe, said switch means further having a calibrating position for applying to the first mixer means said reference frequency fo and said ancillary frequency fc to synthesize said first beat frequency fi1 therefrom; a first band-pass filter, with a pass band including said first beat frequency fi1, connected between said first mixer means and the second mixer means for delivering to the latter said first beat frequency fi1, said second mixer means being further connected to said source for receiving therefrom in each of said positions said ancillary frequency fc to generate a second beat frequency fi2 fo; a second band-pass filter, with a narrow pass band centered on said second beat frequency fi2, connected in the output of said second mixer means for receiving therefrom said second beat frequency f12; amplitude-indicating means connected to said second mixer means for receiving said second beat frequency fi2 therefrom; and amplitude-adjusting means between said second mixer means and said amplitude-indicating means for setting same, in said calibrating position, to a selected reference value.