A ground-vehicle-speed signal processing circuit for a skid control device is disclosed in which, when one or more pulses are dropped from a vehicle-speed signal detected by a Doppler radar vehicle speed sensor, the vehicle-speed output voltage is decreased in accordance with the deceleration just prior to the moment when the pulses are dropped, which is stored in a memory device, to generate a vehicle-speed signal having compensated appropriately the missing part in the detected signal.

A signal locating apparatus for locating within a frequency band an input signal of a first frequency, the signal locating apparatus including a signal receiver for receiving the input signal. The signal receiver is characterized by having a relatively narrow bandwidth response of variable center frequency, the signal receiver being capable of generating a detected signal when the center frequency is substantially equal to the first frequency, the signal locating apparatus further including search device for varying the center frequency at a relatively high rate so as to cause the signal receiver to search for the presence of the input signal within a frequency band, the search device being operable in response to generation of the detected signal to stop the search for the presence of the input signal. The signal receiver includes an oscillator of variable frequency which determines the center frequency, a mixer receiving the input signal and operative to generate an intermediate frequency signal and a demodulator connected to receive the intermediate frequency signal and operative to generate the detected signal upon receipt of the intermediate frequency signal. The search device includes an integrator connected so as to receive the output signal of the demodulator so that the occurrence of the detected signal at the demodulator output causes an abrupt change in the integrator output.

Circuitry for adjusting the resonant frequency of an Yttrium-Iron-Garnet (YIG) filter in the first local oscillator of a receiver carried on a guided missile is shown to include the combination of a crystal oscillator which produces a pilot signal for tuning the YIG filter to a corresponding resonant frequency and a frequency adjusting arrangement for offsetting the resonant frequency of the YIG filter by a predetermined amount.

Apparatus is provided for determining the frequency of unknown periodic input signals and primarily generally sinusoidal signals which may be accompanied by very substantial noise. More particularly, the system for determining the frequency of unknown periodic input signals accompanied by substantial noise is adapted to a unique traffic radar or doppler radar system. The apparatus includes a phase locked loop in which the incoming signal accompanied by noise is compared with the output from a voltage controlled oscillator to generate a synthetic signal which is substantially free of noise and is well adapted for counting, measuring and display circuitry to give a direct indication of the input signal frequency or a parameter directly related to that input signal frequency. Specifically in doppler radar systems the direct readout is in "miles per hour", a direct function of doppler frequency. The signal which is being subjected to frequency determination is applied directly to the comparator portion of the phase locked loop circuit and it is also applied to the comparator portion of the phase locked loop circuit through a tunable band pass filter whereby speed of response is obtained without loss of noise rejection or frequency or harmonic range. Also an automatic frequency control loop is employed with the comparator to adjust the voltage control oscillator and this AFC loop has adjustable gain which is directly related to the frequency of the incoming signal to enhance the stability over the entire frequency range. The system is also capable of an instantaneous determination of locked operation whereby false readings are avoided.

A signal acquisition circuit for a missile guidance system has a phase lock loop which is responsive to incoming signals received from a target and will lock on to the frequency of the received signal. The bandwidth of the phase lock loop is altered in dependence on the signal being received in order to distinguish between a valid target and noise.