SELECTIVE CALLING SYSTEM PROVIDING AN INCREASED NUMBER OF CALLING CODES OR AUXILIARY INFORMATION TRANSFER

• US 3,702,440 A
• Filed: 11/16/1970
• Issued: 11/07/1972
• Est. Priority Date: 11/16/1970
• Status: Expired due to Term

• Current Assignee: George G. Moore
• Original Assignee: George G. Moore
• Inventors: Moore, George G.
• Primary Examiner(s): Richardson, Robert L.
• Assistant Examiner(s): Weinstein, Kenneth W.
• Application Number:
  US05/089,867
• Time in Patent Office: 722 Days
• Field of Search: 325/55,64,182,302,304,305,306,452,467,466,468 340/171,172,184 343/225,228
• US Class Current: 455/702
• CPC Class Codes: H04W 88/188 using frequency address codes

Abstract

The selective calling system includes a transmitter having first and second signal generators providing sinusoidal and rectangular signals which are combined to form a modulated calling signal. Each receiver of the system includes a first demodulator which demodulates the modulated calling signal and a second demodulator which demodulates the rectangular signal. A frequency selective device connects the first demodulator to a first input of an AND gate and a repetition rate selective device connects the second demodulator to a second input of the AND gate. If the demodulated frequency and repetition rate are within the passbands of the devices, the AND gate provides a turn-on signal which allows primary information to be reproduced by the receiver. The system can be modified so that auxiliary information is transferred to the receivers by the calling signal.

Claims

1. A calling system facilitating the communication of an information signal between a transmitter and selected ones of a plurality of normally silent receivers tuned to the transmitter, the selected ones of the receivers reproducing the information signal in response to a particular amplitude modulated calling signal sent simultaneously with the information signal, such calling system including in combination:

first signal generating means providing sinusoidal calling signals at its output terminals of a plurality of different selected frequencies, which sinusoidal calling signals have amplitudes of a first value;

first selector means having input terminals connected to said output terminals of said first signal generating means and an output terminal, said first selector means being operated to provide a chosen sinusoidal calling signal of a particular frequency at its output terminal;

second signal generating means providing rectangular calling signals at its output terminals of a plurality of different selected repetition rates;

second selector means having input terminals connected to said output terminals of said second signal generating means, said second selector means being operated to provide a chosen rectangular calling signal of a particular repetition rate at its output terminal;

modulating means having an input terminal connected to said output terminal of said first selector means, a control terminal connected to said output terminal of said second selector means and an output terminal, said modulating means changing said amplitude of said first value of said chosen sinusoidal calling signal to a second value which is greater than zero in response to said chosen rectangular calling signal, said modulating means thereby forming an amplitude modulated calling signal at its output terminal; and

first circuit means connecting said output terminal of said modulating means to the transmitter.

2. The calling system of claim 1 wherein said modulatinG means is comprised of:

an electron control device having first, second and third electrodes;

first resistor means having a first end connected to said first electrode of said electron control device and a second end;

second circuit means connecting said input terminal of said modulating means to said second end of said first resistor means;

third circuit means connecting said output terminal of said modulating means to said second end of said first resistor means;

fourth circuit means connecting said second electrode of said electron control device to said control terminal of said modulating means;

first circuit means coupling said third electrode of said electron control device to a reference potential, said electron control device being rendered conductive and nonconductive in response to said chosen rectangular calling signal thereby causing said reference potential to be alternately connected to and disconnected from said first end of said first resistor means, said second circuit means and said first resistor means forming a voltage divider only during the times that said electron control device is conductive so that the level of the amplitude of said chosen sinusoidal calling signal varies between said first and second values in response to said chosen rectangular calling signal.

3. The calling system of claim 2 wherein said second circuit means and said third circuit means each include resistor-capacitor networks.

4. The calling system of claim 1 wherein said first circuit means includes a low pass filter having an upper cut-off frequency which is greater than any one of said frequencies of said sinusoidal calling signals.

5. The calling system of claim 1 wherein the maximum of said different selected repetition rates of said rectangular calling signals is less than one-fourth the minimum of said different selected frequencies of said sinusoidal calling signals.

6. The calling system of claim 1 further comprised of a decoder means which includes:

first demodulating means one of which is included in each of the receivers, each of said first demodulating means providing said amplitude modulated calling signal at an output terminal thereof;

frequency selective means one of which is included in each of the receivers, each of said frequency selective means being responsive to a sinusoidal calling signal of a predetermined frequency and having an input terminal and an output terminal;

sixth circuit means connecting output terminal of one of said first demodulating means to said input terminal of one of said frequency selective means, said frequency selective means providing a first control signal at said output terminal thereof in response to said frequency of said chosen sinusoidal calling signal being substantially equal to the predetermined frequency to which said frequency selective means responds;

second demodulating means each having an input terminal connected to said output terminal of one of said first demodulating means and an output terminal, each of said second demodulating means being responsive to said amplitude modulated calling signal to provide said chosen rectangular calling signal at its output terminal;

repetition rate selective means included in each of the receivers, each of said repetition rate selective means being responsive to a predetermined repetition rate and having an input terminal connected to said output terminal of one of said second demodulating means and an output terminal, said repetition rate selective means providing a second control signal at said output terminal thereof in response to said repetition rate of said chosen rectangular calling signal being substantially equal to said predetermined rate; and

gate means included in each of the receivers, each of said gate means having a first input terminal connected to said output terminal of one of said frequency selective means, a second input terminal connected to said output terminal of one of said repetition raTe selective means, and an output terminal, said gate means being responsive to said first and second control signals to provide a turn-on signal which enables the selected normally silent receiver to reproduce the information signal.

7. The calling system of claim 6 wherein each of said frequency selective means includes an electromechanical frequency responsive device.

8. The calling system of claim 6 wherein said sixth circuit means includes a low pass filter having an upper cut-off frequency which is only slightly greater than the maximum frequency of said selected frequencies of said sinusoidal calling signals.

9. The calling system of claim 6 wherein said second demodulating means includes:

an amplifier means having input, output and control terminals, said input terminal being connected to said output of said first demodulating means so that said amplitude modulated calling signal is applied thereto; and

automatic gain control means having an input terminal connected to said output terminal of said amplifier means and an output terminal connected to said control terminal of said amplifier means, said automatic gain control means being responsive to said first and second values of the amplitude of said amplitude modulated calling signal to provide said chosen rectangular calling signal at said output terminal thereof.

10. In a selective calling system having a transmitter with a signal generator providing a continuous sinusoidal calling signal having an amplitude of a first magnitude and any one of a plurality of different selected frequencies, a primary information supply providing an information signal, and a master modulator connected with said signal generator and said primary information supply for developing a composite signal which is transmitted, and a plurality of normally silent receivers each of which includes a first demodulator, an information reproducing stage, a switchable circuit connected between the first demodulator and an information reproducing stage, the switchable circuit being normally nonconductive and being rendered conductive in response to a turn-on signal, a frequency selective device which is connected between the output of the first demodulator and the switchable circuit and which is responsive to a sinusoidal calling signal of a predetermined frequency provided by the signal generator of the transmitter to provide the turn-on signal which renders the switchable circuit conductive only during the existence of the sinusoidal calling signal, the improvement including in combination:

amplitude modulator means included in the transmitter and having input, output and control terminals, said input terminal being connected to the output of the signal generator, said output terminal being connected to the master modulator of the transmitter;

auxiliary information supply means included in the transmitter providing a rectangular information signal to the control terminal of said amplitude modulator means so that the amplitude of the sinusoidal calling signal is selectively changed between the first magnitude and a second magnitude in response to said rectangular information signal thereby forming an amplitude modulated information signal;

second demodulator means included in each of the receivers and connected to the output of the first demodulator, said second demodulator means being responsive to said amplitude modulated information signal to provide said rectangular information signal at the output terminal thereof; and

data utilization means connected to said output terminal of said second demodulator means, said data utilization device being adapted to make use of said rectangular information signal.

11. The combination of claim 10 wherein said amplitude modulator means is comprised of:

an electron control device having first, second and third electrodes;

first circuit means coupling said first electrode of said electron control device to said input terminal of said amplitude modulaTor means and to said output terminal of said amplitude modulator means;

second circuit means connecting said second electrode of said electron control device to said control terminal of said amplitude modulator means; and

third circuit means coupling said third electrode of said electron control device to a reference potential, said electron control device being rendered conductive and nonconductive in response to said rectangular information signal thereby causing said reference potential to be alternately connected and disconnected to and from said first circuit means, said first circuit means cooperating with said reference potential to form a voltage divider so that the amplitude of the sinusoidal calling signal varies between said first and second magnitudes in response to said rectangular information signal.

12. The combination of claim 10 wherein said second demodulating means includes:

amplifying means having input, control and output terminals, said input terminal of said amplifying means being connected to the first demodulating means so that said amplitude modulated information signal is applied to said amplifying means; and

automatic gain control means having an input terminal connected to said output terminal of said amplifying means and an output terminal connected to said control terminal of said amplifying means;

said automatic gain control means being responsive to said first and second magnitudes of the amplitude of said amplitude modulated information signal to develop at said output terminal thereof the rectangular information signal provided by said auxiliary information supply means of the transmitter.

13. The calling system of claim 1 wherein said amplitude of said second value of said sinusoidal calling signal is on the order of 75 percent of said amplitude of said first value to minimize the creation of spurious emanations from the transmitter.

14. In a calling system having a transmitter which provides a composite signal made up of an information component and an amplitude modulated calling signal, the amplitude modulated calling signal being made up of a sinusoidal calling signal having a chosen frequency which is modulated by a rectangular calling signal having a chosen repetition rate, and a decoder means associated with a plurality of normally silent receivers, the decoder means being responsive to a particular amplitude modulated calling signal to render a selected receiver operative, the decoder means being comprised of:

first demodulating means included in each of the receivers, each of said first demodulating means providing said amplitude modulated calling signal at an output terminal thereof;

frequency selective means included in each of the receivers, each of said frequency selective means being responsive to a sinusoidal calling signal of a predetermined frequency and having an input terminal coupled to said output terminal of one of said first demodulating means and an output terminal;

said frequency selective means providing a first control signal at said output terminal thereof only in response to said frequency of said chosen sinusoidal calling signal being substantially equal to the predetermined frequency to which said frequency selective means responds;

second demodulating means included in each of the receivers, each of said second demodulating means having an input terminal connected to said output terminal of one of said first demodulating means and an output terminal;

each of said second demodulating means being responsive to said amplitude modulated calling signal to provide said chosen rectangular calling signal at its output terminal;

repetition rate selective means included in each of the receivers, each of said repetition rate selective means being responsive to a predetermined repetition rate and having an input terminal connected to said output terminal of one of said second demodulating means and an output terminal, said repetition rate selective means providIng a second control signal at said output terminal thereof only in response to said repetition rate of said chosen rectangular calling signal being substantially equal to said predetermined rate; and

gate means included in each of the receivers each of said gate means having a first input terminal connected to said output terminal of one of said frequency selective means, a second input terminal connected to said output terminal of one of said repetition rate selective means, and an output terminal, said gate means being responsive to the simultaneous existence of said first and second control signals to provide a turn-on signal which enables the selected normally silent receiver to reproduce the information signal.

15. The calling system of claim 14 wherein said second demodulating means includes:

an amplifier means having input, output and control terminals, said input terminal being connected to said output of said first demodulating means so that said amplitude modulated calling signal is applied thereto; and

automatic gain control means having an input terminal connected to said output terminal of said amplifier means and an output terminal connected to said control terminal of said amplifier means, said automatic gain control means being responsive to said first and second values of the amplitude of said amplitude modulated calling signal to provide said chosen rectangular calling signal at said output terminal thereof.