Recognition system

Claim 2

An electronic recognition system comprising transmitting means for transmitting an amplitude modulated signal; target means adapted to receive said modulated signal for generating a harmonic signal having a plurality of signal components, having respective amplitudes, said target means further comprising amplitude varying means for varying the amplitude of at least one of said plurality of signal components to obtain an output signal having a preselected coded arrangement of the amplitudes of said plurality of signal components; and receiving means responsive to said output signal, said receiving means comprising sensing means for producing a recognition signal when said preselected coded arrangement of amplitudes of said plurality of signal components is received.

Claim 3

An electronic recognition system as in claim 1, in which said transmitting means comprises signal-producing means for producing a signal of preselected frequency, and modulator means for amplitude modulating said signal of preselected frequency.

Claim 4

An electronic recognition system as in cliam 1, in which said transmitting means includes signal-producing means for generating at least two signals for different preselected frequencies.

Claim 5

An electronic recognition system as in cliam 1, in which said transmitting means includes signal-producing means for generating at least two signals for different preselected frequencies.

Claim 6

An electronic recognition system as in claim 1, in which said target means comprises a harmonic generator for generating at least a harmonic signal from said modulated signal, detecting means for detecting the amplitude modulating signal, means for applying the detected signal to said amplitude varying means, and modulating means for modulating said harmonic signal with the signal from said amplitude varying means.

Claim 7

An electronic recognition system as in claim 1, in which said target means further comprises a diode connected across said amplitude varying means.

Claim 8

An electronic recognition system as in claim 1, in which said amplitude varying means comprises a frequency selective network for altering at least one of said plurality of signal components.

Claim 9

An electronic recognition system as in claim 1, in which said amplitude varying means comprises a plurality of frequency selective networks for altering different ones of said plurality of signal components.

Claim 10

An electronic recognition system as in claim 7, and disabling means for selectively disabling predetermined ones of said plurality of frequency selective networks.

Claim 11

An electronic recognition system as in claim 1, in which said amplitude varying means comprises a tuned circuit which is tuned to the frequency of one of said signal components.

Claim 12

An electronic recognition system as in claim 1, in which said transmitting means comprises at least one signal generator for generating a signal of pre-selected frequency, and said receiving means includes multiplying means connected to said transmitting means for multiplying said signal of preselected frequency to produce a component signal of said harmonic signal, mixing means for mixing said received harmonic signal with said multiplied signal, said sensing means comprising comparing means for comparing the amplitudes of said received signals and for producing said recognition signal when the amplitudes of said signal components are in said preselected arrangement.

Claim 13

An electronic recognition system as in claim 10, and an alarm device responsive to said recognition signal for producing an indication that said recognition signal has been generated.

Claim 14

An electronic recognition system as in claim 2, in which said modulating means comprises at least two signal generators for modulating said signal of preselected frequency with modulating signals of different frequencies.

Claim 15

An electronic recognition system as in claim 2, in which said modulator means comprises a variable frequency signal generator for modulAting said signal of preselected frequency with a signal the frequency of which varies with time.

Claim 16

An electronic recognition system as in claim 13, in which said sensing means further comprises amplitude responsive means for generating a signal proportional to the amplitude of said received signal.

Claim 17

An electronic recognition system as in claim 14, and alarm means connected to said amplitude responsive means for producing said recognition signal when the amplitude of the signal from said amplitude responsive means reaches a preselected value.

Claim 18

A recognition system comprising transmitting means for transmitting an amplitude modulated signal comprising a plurality of signal components, a target comprising harmonic generator means operable to receive said amplitude modulated signal for generating a harmonic output signal, detecting means for producing a detected signal comprising at least some of the components of the amplitude modulated signal, modulating means for modulating said harmonic output signal with said detected signal, and a frequency selective network for altering the amplitude of at least one of the components comprising said detected signal to produce a coded arrangement of signal components which comprise said harmonic output signal; and receiving means for producing a recognition signal when said coded arrangement of signal components is sensed.

Claim 19

A recognition system comprising transmitting means for transmitting an amplitude modulated signal comprising a plurality of signal components, a target comprising harmonic generator means operable to receive said amplitude modulated signal for generating a harmonic output signal, detecting means for producing a detected signal comprising at least some of the components of the amplitude modulated signal, modulating means for modulating said harmonic output signal with said detected signal, and a frequency selective network for altering the amplitude of at least one of the components comprising said detected signal to produce a coded arrangement of signal components which comprise said harmonic output signal; and receiving means for producing a recognition signal when said coded arrangement of signal components is sensed.

Claim 20

A recognition system as in claim 16, in which said transmitting means comprises oscillator means for generating at least two signals of different preselected fundamental frequencies, and an antenna for radiating said two signals to produce a composite amplitude modulated signal which is modulated by a signal having a frequency equal to the difference in frequency between said two signals.

Claim 21

A recognition system as in claim 16, in which said harmonic generator means, detecting means and modulating means comprise a diode connected across said frequency selective network.

Claim 22

A recognition system as in claim 16, in which said frequency selective network is a parallel resonant circuit.

Claim 23

A recognition system as in claim 16, in which said frequency selective network is a series resonant circuit.

Claim 24

A recognition system as in claim 16, in which said frequency selective network comprises a resistor connected to a reactive element.

Claim 25

A recognition system as in claim 16, in which said frequency selective network comprises a filter having a plurality of stop bands.

Claim 26

A recognition system as in claim 22, and switch means connected to said filter for selectively varying the stop bands of said filter.

Claim 27

A target for use with a recognition system adapted to produce an amplitude modulated signal at said target, said target comprising harmonic means for generating a harmonic of said amplitude modulated signal, detecting means for detecting the amplitude modulated signal, amplitude varying means for varying the amplitude of preselected components in said detected signal, and modulating means for modulating the harmonic signal with the signal from said amplitude varying means to produce an otuput signal having a predetermined coded arrangement of signal components.

Claim 28

A target for use with a recognition system adapted to produce an amplitude modulated signal at said target, said target comprising harmonic means for generating a harmonic of said amplitude modulated signal, detecting means for detecting the amplitude modulated signal, amplitude varying means for varying the amplitude of preselected components in said detected signal, and modulating means for modulating the harmonic signal with the signal from said amplitude varying means to produce an otuput signal having a predetermined coded arrangement of signal components.

Claim 29

A target as in claim 24, in which said amplitude varying a frequency comprises afrequency selective network.

Claim 30

A target as in claim 25, in which said amplitude varying means comprises a plurality of frequency selective networks.

Claim 31

A target as in claim 26, and selectively operable disabling means for disabling desired ones of said plurality of frequency selective networks.

Claim 32

A target as in claim 24, in which said harmonic means, detecting means and modulating means comprise a diode.