Rf transmission and detection system

Claim 2

A 2transponder system responsive to input signals encoded in the form of FSK signals having at least two frequencies including in combination: a variable frequency oscillator providing signals controlling the frequency of operation of the output of said transponder system, the frequency of the oscillator being determined by a DC control voltage; comparison means responsive to the input signals and to the output of the oscillator for providing a control voltage, the value of which is a function of the relative frequencies of the input signals applied thereto; means for applying the control voltage to the oscillator to control the frequency of operation thereof accordingly; and threshold means responsive to the control voltage over a predetermined value to provide one output and for providing a different output for the control voltage below said predetermined value to decode said input signals.

Claim 3

The combination according to claim 1 further including means for modulating the oscillator output to provide output signals from said transponder.

Claim 4

The combination according to claim 2 further including a transmitter driver responsive to the output of the oscillator for supplying signals to an antenna and wherein the modulating means operates to key the output of the transmitter driver on and off in accordance with a signal train to be transmitted, the transmitted frequency being controlled by the frequency of the oscillator.

Claim 5

The combination according to claim 1 wherein the comparison means includes a bistable multivibrator and a low pass filter, the output of the multivibrator being supplied to the input of the low pass filter, the output of which is the control voltage, the bistable multivibrator having set and re-set inputs, with the input signals being applied to one of said inputs and with the output of the variable frequency oscillator being supplied to the other of said inputs.

Claim 6

The combination according to claim 4 wherein the threshold means includes a threshold trigger circuit providing a first output in response to the control voltage over said predetermined value and providing a second output in response to the control voltage below said predetermined value.

Claim 7

The combination according to claim 5 wherein the trigger circuit is a Schmitt trigger circuit.

Claim 8

A radio frequency transmission and detection system having an interrogation station for supplying interrogation station signals and a transponder for receiving the interrogation station signals and transmitting reply signals to the interrogation station, including in combination: a master frequency oscillator at the interrogation station for controlling the frequency of the interrogation station signals; an interrogation station receiver having a mixer supplied with an injection signal obtained from the master frequency oscillator; a transponder oscillator in the transponder; means in said transponder responsive to received signals from the interrogation station for varying the frequency of the transponder oscillator in accordance with the frequency of the received interrogation station signals; transmitter means in the transponder controlled by the output of the transponder oscillator for transmitting signals to the interrogation station receiver; and means in the interrogation station for supplying received signals from the transponder transmitter means to the mixer, the bandwidth requirements of the interrogation station receiver being narrow, since both the injection and received signals supplied to the mixer thereof are directly related to the same master frequency oscillator.

Claim 9

A radio frequency transmission and detection system having an interrogation station for supplying interrogation station signals and a transponder for receiving the interrogation station signals and transmitting reply signals to the interrogation station, including in combination: a master frequency oscillator at the interrogation station for controlling the frequency of the interrogation station signals; an interrogation station receiver having a mixer supplied with an injection signal obtained from the master frequency oscillator; a transponder oscillator in the transponder; means in said transponder responsive to received signals from the interrogation station for varying the frequency of the transponder oscillator in accordance with the frequency of the received interrogation station signals; transmitter means in the transponder controlled by the output of the transponder oscillator for transmitting signals to the interrogation station receiver; and means in the interrogation station for supplying received signals from the transponder transmitter means to the mixer, the bandwidth requirements of the interrogation station receiver being narrow, since both the injection and received signals supplied to the mixer thereof are directly related to the same master frequency oscillator.

Claim 10

The combination according to claim 7 further including means for varying the frequency of the master frequency oscillator so that the interrogation station signals are in the form of FSK signals.

Claim 11

The combination according to claim 8 wherein the transponder oscillator is a variable frequency oscillator, the frequency of which is determined by a DC coNtrol voltage applied thereto; and the means in said transponder responsive to signals received from the interrogation station for varying the frequency of the transponder oscillator also is responsive to the transponder oscillator output signals for providing a control voltage which is a function of the relative frequencies of said two signals and includes means for applying said control voltage to the transponder oscillator to control the frequency thereof accordingly.

Claim 12

The combination according to claim 9 further including threshold means responsive to said control voltage over a predetermined value for providing one output and responsive to said control voltage below said predetermined value for providing a different output.

Claim 13

The combination according to claim 10 further including means for keying the output of the transponder transmitter means in accordance with signals to be transmitted therefrom.

Claim 14

The combination according to claim 10 wherein the means for providing the control voltage includes a low pass filter and a bistable multivibrator having at least one output and first and second inputs, with the multivibrator output being coupled to the low pass filter, the output of which is said control voltage, with the first multivibrator input being supplied with input signals received from the interrogation station and with the second multivibrator input being supplied with the output of the transponder oscillator, signals applied to the first multivibrator input causing the multivibrator to assume a first state of operation and signals applied to the second multivibrator to assume a second state of operation.

Claim 15

The combination according to claim 12 wherein the threshold means includes a threshold trigger circuit responsive to the output of the filter to produce an output signal train which corresponds to the signal train supplied by the interrogation station.