GB871773A - Means for measuring rate of change of frequency - Google Patents

Abstract

871,773. Frequency detectors; radio navigation. COLLINS RADIO CO. Aug. 14, 1959 [Jan. 2, 1959], No. 27877/59. Classes 40(5) and 40(7) [Also in Group XXXVI] Apparatus for measuring the rate of change of frequency of a signal comprises a first and a second mixer, means for delaying the signal and for supplying the delayed signal to the first and second mixers, means for supplying the signal directly to the first mixer, and a phase shifter for changing the phase of the signal and applying the result of the second mixer; the outputs of such mixers being combined in means producing a rotating magnetic field associated with further means for measuring the angular velocity of rotation of such rotating field. A variable frequency signal derived, e.g. by reflection or transmission by a moving object with a rate of frequency change determined by the radial acceleration of such object excites receiver 11 (Fig. 1) energizing mixer 16 both directly and through time delay network 13 and also energizing mixer 17 both through the time delay network and through a quadrature network 12. The mixer outputs in quadrature represent in frequency the rate of frequency change of the input signal and energize an electro mechanical device 36 producing a rotational velocity determined by the angular velocity of a rotating field produced by the outputs. The device may comprise (Fig. 3) a 400 c.p.s. chopper 42 producing at the outputs of filters 47, 48 signals at 400 c.p.s. modulated by the quadrature outputs of the mixers (Fig. 4 not shown) which energize the stator windings of a biphase resolver 53 to produce a rotating magnetic field. The voltage induced in the rotor winding operates biphase servomotor 56 through servo amplifier 54 to drive the rotor at a speed proportional to the input signal rate of frequency change at which the amplifier input is a null and the rotor follows the field rotation. A biphase tachometer generator 60 has one winding energized from the 400 c.p.s. source so that the other develops an alternating signal, representing in amplitude the rate of change of input signal frequency, fed back to the rotor circuit of resolver 53 to prevent hunting and rectified by 400 c.p.s. chopper 66 and capacitance 68 to develop a unidirectional voltage representing rate of input frequency change, measurable by a meter (not shown). The quadrature network may be connected in the delay network input (Fig. 5, not shown).