Vehicle detection system and method of operation

Claim 3

A method according to claim 1, in which the amplitude of said fourth signal which will develop an output signal is increased as said signal-to-noise ratio reduces and is reduced as said signal-to-noise ratio increases.

Claim 4

A method according to claim 2, in which the amplitude of the said fourth signal at which an output signal is produced is reduced to a predetermined minimum as said signal-to-noise ratio increases and then remains substantially constant during further increases in signal-to-noise ratio.

Claim 5

In a land vehicle detection system: means to detect and amplify a predetermined band width of the acoustical spectrum from a land vehicle, phase lock loop means for tracking a selected spectral line of said band width and operable to develop a voltage signal which varies in frequency and amplitude in conformity with the amplitude and frequency of variations in frequency of said selected spectral line, a threshold component connected to receive said voltage signal and operable to produce an output signal at a predetermined level of amplitude and frequency of said voltage signal, and means for adjusting said level in conformity to the signal-to-noise ratio in the said band width.

Claim 6

In a land vehicle detection system: means to detect and amplify a predetermined band width of the acoustical spectrum from a land vehicle, phase lock loop means for tracking a selected spectral line of said band width and operable to develop a voltage signal which varies in frequency and amplitude in conformity with the amplitude and frequency of variations in frequency of said selected spectral line, a threshold component connected to receive said voltage signal and operable to produce an output signal at a predetermined level of amplitude and frequency of said voltage signal, and means for adjusting said level in conformity to the signal-to-noise ratio in the said band width.

Claim 7

A land vehicle detection system according to claim 4, in which said level is adjusted downwardly for increases in said ratio and upwardly for decreases in said ratio.

Claim 8

A land vehicle detection system according to claim 5, in which said level is adjusted instantaneously and continuously during operation of said system.

Claim 9

A land vehicle detection system according to claim 5, which includes means for measuring the signal-to-noise ratio in said band width and for generating a control voltage which varies in conformity with said ratio, said threshold component having a control terminal sensitive to the supply of a voltage thereto to adjust the said level at which said threshold component produces an output signal, said control terminal being connected to receive said control voltage and reducing the said level as said signal-to-noise ratio increases and vice versa.

Claim 10

A land vehicle detection system according to claim 4, in which said means for detecting and amplifying a predetermined band width of the acoustical spectrum comprises: a microphone, an amplifier supplied by said microphone and a first band pass filter supplied by said amplifier and passing said predetermined band width, said phase lock loop means comprising a mixer receiving the output from said first band pass filter as a first input signal, a second band pass filter receiving the output from said mixer, a voltage controlled oscillator receiving the output from said second band pass filter as a control signal and developing an output signal having a frequency which varies according to variations in the voltage of the output from said second band pass filter, said mixer receiving the output from said oscillator as a second input signal, a third band pass filter receiving the output from said second band pass filter, a threshold component receiving the output from said third band pass filter as an input signal and operable at a predetermined level of said input signal to supply an output signal, means for measuring the signal-to-noise ratio in the said predetermined band width and for developing a control voltage which varies in conformity with said ratio, said threshold component having a terminal sensitive to the supply of voltage thereto to adjust the said level of the input signal thereto at which an output signal will be developed thereby, and means for supplying said control voltage to said terminal.

Claim 11

A land vehicle detection system according to claim 8, in which said level is adjusted downwardly as said ratio increases and upwardly as said ratio decreases.