Diversity rf alarm system

Claim 2

An alarm system for indicating at a central receiving location which of a plurality of remotely located alarm condition sensing units has triggered comprising, a plurality of remotely located alarm condition sensing units, each sensing unit being comprised of at least one sensing means which is comprised of an alarm condition sensing element connected to a frequency diversity radio transmitter means, each transmitter means being operative to emit a pair of frequency diversity radio signals when it is triggered by the sensing element to which it is connected, the transmitter means of each unit including means for generating carrier signals of first and second predetermined frequencies and means for modulating said carrier signals with a modulation signal of a single fixed frequency, the modulation signals produced by the transmitter means of each unit being of a different fixed frequency, whereby the transmitter means of each unit when triggered emit frequency diversity carrier signals having the same carrier frequencies as the carrier signals emitted by the transmitter means of each other unit, which carrier signals are modulated with a different fixed modulation frequency than the carrier signals emitted by the transmitter means of each other unit and a frequency Diversity receiver means at said central receiving location including means for selectively passing said first and second predetermined frequencies and further including a demodulation means for demodulating said frequency diversity signals to produce demodulated signals of said different fixed modulation frequencies, and decoder means responsive to said fixed frequency signals for producing a different alarm output signal for each of said different frequencies whereby the alarm condition sensing unit which has triggered is identified, said decoder means comprising a plurality of pulse rate discriminator means, equal in number to the number of sensing units, each pulse rate discriminator means being responsive to a different one of said fixed frequency signals for producing a different alarm output signal.

Claim 3

The system of claim 1 wherein each of said pulse rate discriminator means includes means responsive to the rate of zero axis crossings of said demodulated fixed frequency signals.

Claim 4

The alarm system of claim 1 wherein each of said sensing units is comprised of a plurality of said sensing means.

Claim 5

The alarm system of claim 3 wherein the sensing elements of each sensing unit are responsive to a different condition from the sensing elements of each other sensing unit and wherein each sensing element of a single sensing unit is positioned at a different remote location from the other sensing elements in that unit.

Claim 6

The alarm system of claim 3 wherein the sensing elements of each sensing unit are positioned at a different remote location from the sensing elements of each other unit and wherein each sensing element of a single unit is responsive to a different condition than the other sensing elements in that unit.

Claim 7

The alarm system of claim 1 wherein the at least one sensing element of each sensing unit is responsive to a different condition.

Claim 8

The alarm system of claim 1 wherein the at least one sensing element of each sensing unit is positioned at a different remote location.

Claim 9

The alarm system of claim 1 wherein said receiver means further includes means for producing said different alarm output signals when only one of any pair of frequency diversity signals is received at said receiver means.

Claim 10

The alarm system of claim 1 wherein the signals of each pair of frequency diversity signals are spaced from each other in the frequency spectrum by a small amount compared to the carrier frequency of either of said signals.

Claim 11

The alarm system of claim 9 wherein said means for generating carrier signals of first and second predetermined frequencies includes a subcarrier oscillator means for generating a subcarrier signal having a frequency of half said small amount, a crystal controlled oscillator means for generating a center carrier frequency signal having a frequency midway between said first and second predetermined frequencies and a balanced modulator means connected to said subcarrier oscillator means and to said crystal oscillator means for combining said subcarrier signal and said center carrier frequency signal.

Claim 12

The alarm system of claim 10 wherein said means for modulating said carrier signals comprises a means for amplitude modulating said signal generated by said subcarrier oscillator means.

Claim 13

The alarm system of claim 11 wherein said single fixed frequency is a frequency in the ultrasonic range.

Claim 14

The alarm system of claim 12 wherein said means for amplitude modulating is a relaxation oscillator and said subcarrier oscillator means is a Colpitts type oscillator.

Claim 15

The alarm system of claim 12 wherein said frequency diversity receiver means at said central location is a two channel superhetrodyne type receiver means, each of said channels including means tuned to receive one of said frequency diversity signals of a pair of said frequency diversity signals and local oscillator and mixer means for converting said signals to an intermediate frequency signal, means for switching between said local oscillator and mixer Means of said two channels, and a single intermediate frequency amplifier means for amplifying said intermediate frequency signal.

Claim 16

The system of claim 14 wherein each of said pulse rate discriminator means includes means responsive to the rate of zero crossings of said demodulated fixed frequency signals.

Claim 17

The alarm system of claim 9 wherein said frequency diversity receiver means at said central location is a two channel superhetrodyne type receiver means, each of said channels including means tuned to receive one of said frequency diversity signals of a pair of said frequency diversity signals and local oscillator and mixer means for converting said signals to an intermediate frequency signal, means for switching between said local oscillator and mixer means of said two channels, and a single intermediate frequency amplifier means for amplifying said intermediate frequency signal.

Claim 18

The system of claim 16 wherein each of said tuned means comprises a radio frequency amplifier means.

Claim 19

The system of claim 17 further including a preselector filter means connected to the input of said receiver means.

Claim 20

The alarm system of claim 1 wherein each pulse rate discriminator means includes means for generating a pulse of duration equal to a fixed fraction of the period corresponding to a given one of said modulation frequencies.

Claim 21

The alarm system of claim 19 wherein said means for generating carrier signals of first and second predetermined frequencies includes a subcarrier oscillator means for generating a subcarrier signal having a frequency of half said small amount, a crystal controlled oscillator means for generating a center carrier frequency signal having a frequency midway between said first and second predetermined frequencies, and a balanced modulator means connected to said subcarrier oscillator means to said crystal oscillator means for combining said subcarrier signal and said center carrier frequency signal, and wherein said means for modulating said carrier signals comprises means for amplitude modulating said signal generated by said subcarrier oscillator means and wherein said frequency diversity receiver means at said central location is a dual channel superhetrodyne type receiver means, each of said channels including means tuned to receive one of said frequency diversity signals of a pair of frequency diversity signals, and means for switching between said channels.

Claim 22

The system of claim 1 wherein said means for modulating said carrier signals comprises a means for generating a fixed frequency signal in the ultrasonic range.

Claim 23

An alarm system comprising a plurality of central receiving locations in the same vicinity, a group of alarm condition sensing units being associated with each central receiving location, each sensing unit being comprised of at least one sensing means which is comprised of an alarm condition sensing element connected to a frequency diversity transmitter means for generating a pair of frequency diversity signals, each of said transmitter means including first generating means for generating a center carrier frequency signal for said pair of frequency diversity signals, the center carrier frequency signal generated by said first generating means of the transmitter means of each group being of the same frequency but of different frequency that the signal generated by said first generating means of the transmitter means of each group, each of said transmitter means further including second generating means for generating a fixed frequency modulation signal, the modulation signal generated by said second generating means of the transmitter means of each unit being of a different fixed frequency than the modulation signal generated by said second generating means of the transmitter means of each other unit in the same group, each transmitter means further including means for combining said carrier signals with said modulation signal whereby each transmitter means when triggered emits a pair of frequency dIversity signals having the same center carrier frequency as the signals emitted by each other transmitter means in the same group but a different center carrier frequency than the signals emitted by transmitter means in each other group and having a fixed frequency modulation signal of different frequency than the modulation signal of the signals emitted by transmitter means in other units of the same group, and a plurality of frequency diversity receiver means at said plurality of central receiving locations, neach receiver means including means for selectively passing signals of the center carrier frequency generated by said first generating means of the transmitter means of the group with which said receiver means is associated, and further including a demodulation means for demodulating said frequency diversity signals to produce different fixed frequency demodulated signals, each receiver means further including a plurality of pulse rate discriminator means connected to its output of a number equal to the number of sensing units of the group with which said receiver is associated, each pulse rate discriminator means being responsive to a signal of different frequency to activate a different alarm output, whereby the particular alarm output activated is indicative of both the group and unit of the transmitter means which has triggered.

Claim 24

An alarm system comprising a plurality of central receiving locations in the same vicinity, a group of alarm condition sensing units being associated with each central receiving location, each sensing unit being comprised of at least one sensing means which is comprised of an alarm condition sensing element connected to a frequency diversity transmitter means for generating a pair of frequency diversity signals, each of said transmitter means including first generating means for generating a center carrier frequency signal for said pair of frequency diversity signals, the center carrier frequency signal generated by said first generating means of the transmitter means of each group being of the same frequency but of different frequency that the signal generated by said first generating means of the transmitter means of each group, each of said transmitter means further including second generating means for generating a fixed frequency modulation signal, the modulation signal generated by said second generating means of the transmitter means of each unit being of a different fixed frequency than the modulation signal generated by said second generating means of the transmitter means of each other unit in the same group, each transmitter means further including means for combining said carrier signals with said modulation signal whereby each transmitter means when triggered emits a pair of frequency dIversity signals having the same center carrier frequency as the signals emitted by each other transmitter means in the same group but a different center carrier frequency than the signals emitted by transmitter means in each other group and having a fixed frequency modulation signal of different frequency than the modulation signal of the signals emitted by transmitter means in other units of the same group, and a plurality of frequency diversity receiver means at said plurality of central receiving locations, neach receiver means including means for selectively passing signals of the center carrier frequency generated by said first generating means of the transmitter means of the group with which said receiver means is associated, and further including a demodulation means for demodulating said frequency diversity signals to produce different fixed frequency demodulated signals, each receiver means further including a plurality of pulse rate discriminator means connected to its output of a number equal to the number of sensing units of the group with which said receiver is associated, each pulse rate discriminator means being responsive to a signal of different frequency to activate a different alarm output, whereby the particular alarm output activated is indicative of both the group and unit of the transmitter means which has triggered.