Traffic radar and apparatus therefor
First Claim
1. Apparatus for determining the frequency of an unknown periodic input signal which is in a range including a plurality of harmonics of the lowest frequency in the range and may be accompanied by noise comprising:
- source means providing a periodic output signal of variable frequency, said source means being adapted for locked operation at a sample frequency which is a predetermined multiple of said input signal whereby said periodic output signal is adjustable to match said input signal;
frequency and phase comparator means responsive to said output signal and said input signal and generating a control signal which is applied to said source means to control the frequency thereof; and
input means applying said input signal to said comparator and including tunable band pass filter means tunable over said range and by-pass means in parallel with said tunable band pass filter means applying a portion of said input signal to said comparator by-passing said tunable band pass filter means.
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Accused Products
Abstract
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.
51 Citations
18 Claims
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1. Apparatus for determining the frequency of an unknown periodic input signal which is in a range including a plurality of harmonics of the lowest frequency in the range and may be accompanied by noise comprising:
- source means providing a periodic output signal of variable frequency, said source means being adapted for locked operation at a sample frequency which is a predetermined multiple of said input signal whereby said periodic output signal is adjustable to match said input signal;
frequency and phase comparator means responsive to said output signal and said input signal and generating a control signal which is applied to said source means to control the frequency thereof; and
input means applying said input signal to said comparator and including tunable band pass filter means tunable over said range and by-pass means in parallel with said tunable band pass filter means applying a portion of said input signal to said comparator by-passing said tunable band pass filter means. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 17)
- source means providing a periodic output signal of variable frequency, said source means being adapted for locked operation at a sample frequency which is a predetermined multiple of said input signal whereby said periodic output signal is adjustable to match said input signal;
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10. In doppler radar apparatus for determining the speed of a vehicle, the combination comprising:
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input means for providing a period input signal having a frequency related to the speed of such vehicle; source means for generating a synthetic signal corresponding on phase and frequency to said input signal, said source means being variable over a range including a plurality of harmonics of the lowest frequency in said range; phase and frequency comparator means responsive to said input signal and said synthetic signal to generate a control signal to control said source means and to adjust the synthetic signal to have a predetermined phase and frequency relative to said input signal; digital counter and display means energized from said source means to generate and display a count related to the frequency of said source means; and timer means controlling a counting interval of said digital counter and display means whereby the count during said interval represents the speed of said vehicle, said input means including tunable band pass filter means having a center frequency tunable over said range and by pass means in parallel with said tunable band pass filter means applying a portion of said input signal to said comparator by-passing said tunable band pass filter means. - View Dependent Claims (11, 12, 13, 14, 15, 16, 18)
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Specification