Abstract: Independent communication systems are provided with additional receivers that allow the systems to monitor one another's outbound control signalling channels. Secondary control signalling can be interleaved with the primary control signalling information on this communication resource, which secondary control signalling information is intended for reception and use by the monitoring system.

Abstract: In a communications system, a base station has a memory for storing interval control values representative of time-varying traffic pattern of the communications system. A time-keeping circuit recalls a stored interval control value from the memory according to different time of day and a battery-saving command signal is sent from the base station at variable intervals as a function of the value recalled from the memory. Power supplies of a remote station are interrupted for a constant brief interval in response to the battery-saving signal, so that the remote station is powered for a shorter interval during a light traffic period and for a longer interval during a heavy traffic period. In a preferred embodiment, traffic data is automatically collected from the communications system and the stored interval control values are updated according to the collected traffic data.

Abstract: A repeater (30) is provided for relaying communication between a subscriber unit (24) and a central station (10) when the repeater recognizes transmission from the subscriber unit to the central station but detects a lack of response by the central station to that subscriber unit or when the repeater recognizes a transmission from a subscriber unit (26) requesting the repeater for service. The repeater asks the central station for a channel upon which to communicate. Alternately, a predetermined channel may be used for the relayed communication.

Abstract: A radio transmission system designed to operate on a single defined frequency channel. The system comprises a central receiver (12), at least one transmitter (14) remote from the receiver and a plurality of repeaters (13) arranged in zones (Z1 to Zn) arround the receiver. Each repeater can receive a signal from a transmitter and re-transmit the message so that it eventually reaches the receiver by way of one or more repeaters. The system includes protection means for protecting the message against loss or corruption, for example by using unique time delays before re-transmission or by addressing a certain sequence of repeaters with alternate paths being provided to guard against the message being lost.

Abstract: A moble radio system is disclosed in which communication is established between at least two user-operable stations over one of a plurality of channels by operating the user-operable stations in accordance with the following steps:(1) When in the receive mode (the push-to-talk switch is open):(i) incrementing the channel selector to select a channel;(ii) determining if a carrier signal is present on the selected channel:(iii) if a carrier signal is not present, returning to step (1) (i);(iv) if a carrier signal is present, determining if the selected trunk identification signal is present on the carrier signal;(v) if the selected trunk identification signal is not present, returning to step (1) (i); and(vi) if the selected trunk identification signal is present on the carrier signal, enabling said transmitter for push-to-talk operation.

Abstract: A digitally trunked radio repeater system provides substantial improvements in timeliness of channel acquisition and channel drop, and in reliability of critical control signalling. The system uses a much higher digital signalling rate than is typically found in prior art systems, and uses a control channel to convey digital channel request and assignment messages between the central site and mobile transceivers. The mobile radio transceivers transmit channel requests on the control channel (if no response is received, the mobile retries during a retry time window which increases in duration in dependence on the number of retries). The mobile transceiver switches to a working channel in response to an assignement message received on the control channel. Subaudible digital signals transmitted on the control channel and on active working channels allow late entry, shifting to higher priority calls, and other advanced functions.

Abstract: A cellular communication system booster has plural narrowband and wideband channels each having down mixers, local oscillators, IF filters, and amplifiers for amplifying communication signals. On a narrowband channel preferably not in use, and preferably in a time-multiplexed manner, a reference signal of known signal strength is substituted at the output amplifier in lieu of a normal communications signal. When this amplified reference signal is broadcast at the output antenna a portion of the signal is feed back to the input antenna due to imperfect isolation between the antennas. This feedback signal is measured by a Radio Signal Strength Indicator (RSSI) circuit at the point of its receipt into the IF filter of the narrowband channel. The measured signal strength serves as a measurement of signal isolation/feedback between the antennas.

Abstract: A method for optimizing antenna orientation in a cellular radio telephone system with respect to a predetermined criterion of signal level includes the steps of orienting the antenna in a selected direction, sensing a selected received signal in a predetermined frequency range, mixing the selected received signal with the control signal so as to generate a corresponding intermediate frequency signal in an intermediate frequency transmission path, measuring a selected parameter of the intermediate frequency signal and then altering the orientation of the antenna while subsequently repeating the required steps. The preferred antenna orientation can be determined by examining the results of the various measurements and selecting an antenna orientation which maximizes the signal level of the desired received signal.

Abstract: A trunked radio frequency (RF) repeater system for public service trunking (PST) or the like includes a fault detection system having an RF output power monitoring, over-the-air RF monitoring and other repeater transceiver testing capabilities. An over-the-air monitor continually tests the digital signalling transmitted by different transceivers within the repeater system. The site controller automatically removes transceivers that test faulty, and does not permit tested faulty transceivers to go back on line until they have passed poll response, power output and RF digital signalling tests.

Abstract: A mobile perimeter monitoring system includes a battery powder transmitter adapted to be placed upon the person to be monitored while the system user carries a receiver. The receiver responds to a code transmitted by the transmitter and provides an in-range or out-of-range indication depending upon whether the receiver is within the effective range of the transmitter or outside of its effective range. An adjustment on the receiver allows the user to adjust the effective range of the system for varying environments. The receiver may be operated in an in-range mode or an out-of-range mode to provide both perimeter monitoring capability and the ability to track a transmitter if its moves outside the perimeter.

Abstract: An alternate home channel for a land mobile transmission trunked communication system designates one of a plurality of repeaters for a given site or coverage zone as an alternate home repeater. The control signals transmitted over the subaudio band for all home channels repeaters in that site are also duplicatively transmitted over the subaudio band of the alternate home repeater. Each mobile transceiver will be programmed with two channel numbers. One for the home repeater and the other for the site alternate home repeater. When the power is turned on, the mobile transceiver determines which repeater to monitor by scanning both the home and alternate home channels. When a valid control message is detected on either channel, that channel becomes the monitor channel. Operation of the mobile transceiver is then generally similar to prior operation, with the exception that the monitor channel (either home or alternate home channel) is used instead of just the home channel.

Abstract: An apparatus and method for selecting a number of cellular radio channels to be boosted in a given geographical area provides either F1-F1 or F1-F2 operation. The signals can be boosted at the same frequency with input to output isolation being achieved by the use of directive transmit and receive antennas physically positioned to achieve sufficient isolation. Each signal is individually filtered, amplified, and recombined for transmission. Any number of signals may be accommodated depending upon the number of retransmission channels available. Apparatus is also provided to retransmit a signal at a different frequency from that at which it is received. A tag, typically an audio tone or diminished signal amplitude gap, may be selectively applied to boosted retransmitted signals in order that they may be recognized as such.

Abstract: A trunked communication system wherein channel assignment information is provided to a requesting subscriber unit in a dual word format that includes separate and specific information regarding both a transmit frequency and a receive frequency. The transmit and receive frequency information is provided in a coded form, which can be decoded by the subscriber unit with reference to a table of information stored therein in conjunction with a simple algorithm.

Abstract: A repeater for a wide area coverage multiple repeater system (100) includes a receiver (220) and a transceiver (230). The receiver (220) receives a received signal from a portable or mobile communication unit (130) on an inbound channel. The received signal is routed to a receive signal strength indicator (RSSI), a bit error rate (BER) detector, or a similar devices for differentiating a received signal quality characteristic. The transceiver (230) includes a transmitter (232) for repeating the received signal on an outboard channel and a receiver (234) for monitoring presence of an outboard channel activity. A controller (260) enables the transmitter (232) to retransmit the received signal, based on the received signal quality characteristic, and in absence of the outboard channel activity.

Abstract: A method and apparatus for identifying a radio transmitter. The transient frequency or phase history of the turn-on characteristics of a transmitter is detected and digitized. The history can be analyzed by a microprocessor operating a computer program to gather transient phase information from an unknown transmitter and to classify the transmitter in accordance with a transient characteristic.

Abstract: In a communication system that comprises a plurality of communication resources, a plurality of consoles, a communication resource allocator, and a plurality of subscriber units arranged into a plurality of communication groups, the communication resource allocator comprises memory for storing presented and unpresented communication groups. By storing unpresented communication groups, a console, via an associated operator MUX interface module, may automatically utilize the unpresented communication groups without intervention from an operator of the console.

Abstract: A high-frequency signal booster which has at least one channel unit including a down-converter for converting input signals into intermediate-frequency signals and an up-converter for converting time into output signals. The respective up- and down-converters are separately equipped with station-originating signal oscillators. Further, the station-originating signal oscillator provided for the up-converter has a function of effecting the modulation with out-of-voice-band signals.

Abstract: A redundant repeater connected between two transmission mediums that can operate in a repeat state where packets are repeated between the mediums, and a standby state where no packets are repeated and where the repeater determines whether packets are being properly repeated between the transmission mediums by another device. If the repeater determines that packets are being independently repeated it remains in the standby state, and will attempt to leave the standby state and return to the repeat state only if it determines that packets on one medium are not being repeated to the second medium. Two repeaters can be redundantly connected across the same transmission mediums with one operating in repeat state and the other in standby. If one repeater fails, the other will begin repeating all received packets. The repeater determines whether packets are being properly repeated by detecting overlapping or non-overlapping packets between its two transmission mediums.

Abstract: In a satellite communication system wherein a common channel is used for communication between a central station (10) and a plurality of remote stations (12) through a satellite transponder (11), in order to avoid system down due to fault of transmission of a broadcasting signal with a timing signal by the central station (10), the central station (10) comprises two portions (13, 14) positioned at different locations and a controller (15). When the first portion (13) detects fault of transmission of the broadcasting signal during the first portion (13) operates to communicate with the remote stations (12) under transmission of the broadcasting signal, the controller (15) is notified the fault and starts the second portion (14) in place of the first portion (13) so that the communication is maintained in the system without false. Those portions (13, 14) are assigned with ID numbers and can detect the fault by detecting operation of ID number.

Abstract: A monitoring and alarm system for a radio frequency microwave communications repeater unit. A plurality of signals representative of the status of a corresponding plurality of operating conditions of the repeater unit are simultaneously generated. The signals are time multiplexed to form a combined signal. The combined signal is encoded to form a digital signal of frames of data having a frequency substantially less than the communication signal carrier frequency and preferably less than the communication modulating signal frequency, with a frame being formed of data from each of the status signals. A variable attenuator is responsive to the digital signal for varying the level of the communication signal proportionally with the value of the digital signal. The level-varied communication signal is then retransmitted.

Abstract: A method for calibrating a remote pilot unit is provided wherein both the pilot receiver and the pilot transmitter are calibrated. A test signal of a known magnitude is applied to the pilot unit and the magnitude actually received by the pilot receiver is determined. The two magnitudes are compared and a correction signal is determined. To calibrate the remote transmitter, a signal of a nominal magnitude from the transmitter is applied to a measurement device and the determination is made by the measurement device of the actual magnitude applied. The actual magnitude and the nominal magnitude are compared and a transmitter correction signal is determined. The receiver correction signal and the transmitter correction signal are stored in permanent memory within the pilot unit. This process is repeated at a plurality of frequencies to provide a signature for both the transmitter and the receiver.

Abstract: A test bench is designed to determine the transfer function of a radio link in terms of variations in amplitude and a group propagation time depending on frequency. A transmission section of the test bench comprises an oscillator delivering a pulse signal having a predetermined intermediate frequency, a generator generating an exploration signal having a predetermined low frequency and a marking pulse signal synchronous with the exploration signal, a summator summating the exploration signal and an analog signal into a wobbulation signal, a r.f. wobbulator controlled by the wobbulation signal for producing a wobbulated signal to be transmitted. In a receiving section of the test bench, an analyzer receives the wobbulated signal via said radio link to analyze parameters of the radio link, such as the link group propagation time.

Abstract: A radio frequency proximity sensing apparatus includes a transmitter having an oscillator circuit for propagating a pulsed RF signal and a receiver having a sensor circuit for the detection of the propagated pulsed RF signal. The receiver includes a logic circuit for processing the propagated pulsed RF signal and a plurality of 14-bit oscillator/resistor timers. An alarm in the receiver is controlled by first and second oscillating circuits such that the transmitter and receiver act in unison to actuate the alarm as the receiver and the transmitter are separated by a distance exceeding the effective RF signal range of the transmitter.

Abstract: A radio communication system comprises a base station for periodically transmitting a power saving signal and an information signal, a repeater station for relaying the signals, and a plurality of terminal stations for communicating with the base station through the repeater station. The repeater station includes power saving circuitry which responds to the power saving signal by cutting off power supplies to its major power consumptive components during a preset interval which alternates with an active interval during which power is supplied to the components.

Abstract: In electronic alarm apparatus for monitoring the presence or absence of objects within a given area, a transmitter attachable to an object, a shift register for storing a digital identification code, and an electronic circuit including a time delay circuit for periodically transmitting the digital identification code as a radio frequency signal; a monitor including a logic timing circuit for activating a receiver for receiving the radio frequency signal, a check circuit for comparing the received signal with a stored identification code and audio logic circuit and liquid crystal display for providing audio and visual indications upon failure of receiving a given number of consecutive transmissions from a given transmitter; the transmitter further including tamper switch and tamper flag logic circuit for changing the digital identification code stored in the shift register upon premature removal of the transmitter from the object.

Abstract: A mechanism for avoiding satellite transponder TWT saturation in an ALPC communication network detects the onset of a lockup condition through an avalanche detector. In response to avalanche detection, those links which have been identified as participating in a downlink fade have their ALPC attenuator settings placed at a minimum level, so that the operating point of the transponder TWT may be reduced below the avalanche threshold. Thereafter, as the fade recedes, those units whose ALPC attenuators have minimum power settings may be restored to normal operation. Because the orderwire which couples link quality data from a received terminal monitor unit to transmitter attenuator control units through the avalanche detection and recovery scheme may itself be impacted by a downlink fade, the foregoing scheme is augmented by a lockup detection and avoidance mechanism through which recovery from an actual lockup may take place.

Abstract: A method of transmitting signalling along a bidirectional digital transmission link consists in transmitting from an intermediate equipment of the link a signalling message in two parts. One is a characterizing part the form of which depends on the signalling type and which is substituted for data of one of the digital bit streams carried by the link in the direction from one of the terminals referred to as the processing terminal. The other is a localizing part whose form is independent of the signalling type and which is substituted for data of the digital bit stream carried by the link in the direction towards the other, so-called relay terminal. The relay terminal responds by sending an acknowledgement message to the processing terminal, the time-delay of this relative to the characterizing part being used to identify the sending equipment. A signalling message transmission circuit controls switching circuits inserted into the paths of the digital bit streams carried by the link.

Abstract: Methods and apparatus for evaluating installation of components of a wireless type of alarm system or the like that includes a plurality of satellite stations, each of which includes a sensor and associated transmitter circuitry responsive to the sensor for transmitting an alarm signal and a central station for receiving the alarm signal and operating an output device in response to the received signal. The system includes alarm signal processing circuitry that has a first (normal) mode for processing the received signal and second (installation) mode in which a characteristic of the received alarm signal is impaired so that a received signal of greater quality than in normal mode is required to operate the output device.

Abstract: A satellite communication system between small earth stations through a satellite and a relay earth station. The relay earth station has a larger antenna and a higher power transmitter than those of a small earth station in order to regenerate received digital signals. The transmission power of the relay earth station is controlled according to rain attenuation between the satellite and the small earth station, and/or rain attenuation between the satellite and the relay earth station, so that rain attenuation is compensated by increasing the transmission power of the relay earth station.

Abstract: An optical repeater for an optical digital transmission line has a pair of in-service monitoring circuits (55, 55') each of which includes a flip-flop (57) for dividing frequency of transmission data to derive commands and burst carrier in the first line (54). A counting means (59, 61) is provided for detecting parity errors and counting the errors in an opposite second line (65). A timing generation means (62) is provided for reading out the counting means (61) upon receipt of the burst carrier. A phase modulator (64) provides phase modulation to a clock pulse in an opposite second line (65) according to the output of the timing generation means (62). The number of errors in the second line (65) is stored in the counting means (61) according to commands in a first line (54) from a terminal transmitter (52). The content of the counting means (61) is forwarded to a terminal receiver (66) through phase modulation of clock pulses in a second line (65) upon receipt of the burst carrier.

Abstract: In radio digital transmission system including at least one repeater station, a channel monitoring circuit of each repeater station comprises, besides the conventional inter-terminals fault detection circuit using parity check system, a control bit inserting circuit for inserting a parity control bit into the received signal, a control bit extracting circuit for extracting the control bit from the received signal, a logic circuit for logically operating the output signal of the conventional fault detection circuit and the output signal of the control bit extracting circuit, and a second fault detecting circuit responsive to the output signal of the logic circuit for detecting the fault on the transmitting line between the repeater station and an immediately preceding station.

Abstract: A remote surveillance utilizing signalling incorporated in traffic and concerns more particularly digital links using a prohibited configuration code for the line signal. The purpose is to produce a system consisting of periodically incorporating an interrogation identifier containing a prohibited configuration in the line signal at the transmitter terminal, recognizing the interrogation identifiers as they pass through equipment under remote surveillance, modifying one interrogation identifier out of r by equipment that has remote surveillance data to be transmitted, using the interrogation identifiers reaching the receiving terminal intact to determine those time slots occupied by the remote surveillance signal and extracting the identifiers occupying these time slots for decoding the remote surveillance.

Abstract: The invention provides apparatus for evaluating installation of components of a wireless type of alarm system or the like that includes a plurality of satellite stations, each of which includes a sensor and associated transmitter circuitry responsive to the sensor for transmitting an alarm signal at radio frequency, and a central station for receiving the alarm signal and operating an output device in response to the received signal. The installation evaluating apparatus includes signal strength sensing circuitry responsive to the strength of the alarm signal received at the central station, and an RF transmitter responsive to the sensed signal strength for transmitting an indicator signal to a receiver at the installation location of the satellite transmitter device being evaluated, the nature of the indicator signal received at the transmitter site providing an indication of the quality of the RF transmission path between the transmitter and the central receiver.

Abstract: A communication system includes a common receiver unit and a plurality of satellite transmitter units remote from the receiver unit. Each transmitter unit has a logic section and a transmitter section, and each transmitter unit is switchable between a standby mode in which no message is to be sent to the receiver unit and an active mode in which a message is to be sent to the receiver unit. The logic section generates status messages and data messages, the format of the status message including an address portion identifying the transmitter unit and an indicator portion shiftable between first and second values. During a standby mode, the transmitter unit periodically and repetitively generates status messages in which the indicator portion is set to the first value, and only during an active mode of the transmitter unit when the transmitter section is sending a message to the receiver unit, the indicator portion of the status message is switched to the second value.

Abstract: A CATV system includes terminal units with which two-way data communication with a central terminal is possible. A cable network monitoring system is capable of assisting in the location of faults by sending data such as the received signal strength at various points of the network back to the central station for analysis.

Abstract: An active repeater for a star configured communications network includes a threshold detector for collision detection. Whenever two or more terminals simultaneously feed data into the repeater, a threshold sensitive collision detector is triggered to logically isolate the data from the output of the repeater and to logically substitute a predetermined collision signal therefor, thereby causing the competing terminals to reset to retry the transmissions at randomly selected later times.

Abstract: An alarm circuit operatively associated with a phase-locked loop provides an error indication when the phases of the referenced signal and voltage controlled oscillator signal lose synchronization for times less than one millisecond. The alarm circuit includes an amplifier connected to receive the phase detector error signal, and an impedance connected to conduct the phase detector error signal to the amplifier. The impedance and amplifier have a frequency response corresponding to a frequency response of an associated receiver circuit, so that short duration deviations in the reference signal frequency which the receiver circuit cannot track produce an error indication and long duration deviations which can be tracked by the receiver circuit do not produce an error indication.

Abstract: In a repeater for a communication system a continuously running local oscillator (P) injects a pilot tone into the repeater input, ahead of all the non-linear functions. The repeater may include an input amplifier 1, a re-shaping amplifier 2 and an output amplifier 3. The pilot frequency is unique to the repeater and is sufficiently close to the clock frequency in a digital system or the carrier frequency in an analogue system to allow the pilot to pass through all the repeater filters. The pilot effects a small phase modulation of the carrier or clock. Measurement of the amount of phase modulation and also the pilot amplitude at the receiving terminal indicates degradation or failure of the system performance. The pilot frequency is used to identify the repeater.

Abstract: A status monitor for coaxial cable networks is disclosed. The monitor is designed to be directly attached to an output port of an amplifier/repeater in the network and is used as an aid in trouble shooting faults in the network. The monitor comprises a detector (12 or 40) which generates a d.c. voltage indicative of the level of a pilot frequency signal on the network. This d.c. voltage is supplied to a plurality of voltage comparators (18, 20 and 22) which compare the d.c. voltage with different reference voltages in order to sense different fault conditions. If a fault condition is sensed, the outputs of the comparators are used by a tone selection logic (24) and an OR logic switch (26) to control a voltage controlled oscillator (28) to generate a modulating tone. A signal from a crystal controlled oscillator (32) or an IF output of the detector (40) is modulated by the tone produced by the voltage controlled oscillator and radiated.

Abstract: This invention is directed to a same frequency repeater (SFR) for use in a multiple SFR system in which only one SFR at a given time is allowed to retransmit a received signal thereby preventing simulcast distortion which could occur due to multiple SFR retransmissions. The SFR includes a receiver for receiving a signal carrying information at a given frequency and a transmitter for rebroadcasting the received signal at the given frequency. A mechanism is provided for keying the transmitter upon the reception of a received signal. A detector senses if a predetermined pilot tone is carried by the received signal. A mechanism responsive to the detection of the pilot tone inhibits the keying of the transmitter if the pilot tone is detected before the transmitter is keyed. A tone generator encodes the output signal of the transmitter with the pilot tone.

Abstract: A repeatered, multichannel fiber optic communication network includes a plurality of full duplex fiber optic channels and one or more auxiliary channels. In order to supervise and control the operation of the network, for both data transmission and fault/maintenance actions, each terminal station contains a processor-based subsystem capable of network monitoring, first level maintenance action, fault isolation, and remote network control and status reporting. This processor-based subsystem interfaces with each fiber optic channel, with an orderwire communication link, and with external input/output devices and surveillance equipment. Three substantially autonomous processor-based sections which are dedicated to performing specific functions within the overall network operation are employed for carrying out these separate interfacing tasks.

Abstract: An orderwire communication scheme for a fiber optic communication network includes terminal station equipment associated with the central offices at opposite ends of the network and signal regenerator equipment at the repeater sites disposed between the terminal stations. The communication format along the link is a data-over-voice scheme, the data being digitally encoded on an FSK modulated carrier. In carrying out supervisory functions with respect to each of the stations along the link, command messages are conveyed from the terminal stations at one of the central offices to respective stations along the link in the form of command instructions. Each command message from a central office's terminal station contains the address of the recipient station for whom the message is intended followed by a specific encoded instruction.

Abstract: An orderwire scheme for a multichannel repeated communication network contains an auxiliary communication link that is coupled to communication sites along the network and is configured of a pair of orderwire links each formed of a conventional interstitial copper wire pair. To carry out supervisory functions with respect to each of the stations along the communication link, messages are conveyed from a control facility coupled to or as part of the network to respective stations along the link in the form of command instructions. These messages may contain a request for information from the addressed site as to equipment conditions at the site or a directive that the equipment at the site perform a particular task. In reply to the command message sent to it the addressed site returns a response message back to the control facility representative of the action taken including any data requested by the instructions.

Abstract: An emergency signal transceiver for a disabled vehicle for generating a repetitive pulse signal, digital apparatus for producing a pulse signal from such a received repetitive pulse signal for actuating buzzer and light alarm displays, apparatus for alternatively switching the pulse signal generator to provide input to a transmitter and the digital apparatus to derive the output of a receiver.

Abstract: The present invention relates to a device for measuring in operation the non-linearity of equipment for the transmission of composite television signals. It comprises a processing circuit which samples an intermodulation product located outside the useful spectrum transmitted, but within the band of the equipment generating it, whose measurement is validated by a control circuit for predetermined instantaneous or average values of the vision carrier.

Abstract: A voltage comparator compares the DC current in active elements of a trunk amplifier with a variable reference voltage for detecting when to switch to a bypass mode. Its output is normally low for passing a current through it, an LED, and relay coils when the amplifier operates satisfactorily.

Abstract: This test equipment permits a testing of the demodulator of a teletex television receiver. It consists of a digital test signal generator, the output of which is connected to the HF input of the television, and a receiver, the input of which is connected to the video output of said receiver. The generator tramsmits pseudo-random data packets having a first frequency of binary elements, with two double-intervaled binary elements at two predetermined instants t.sub.1 and t.sub.2 for each packet. The receiver has a data regeneration circuit whose threshold varies line by line from a maximum value to a minimum value. The sampling clock of the receiver is at a second frequency lower than the first by the ratio (n-2)/n, where n is equal to the integral ratio of the first frequency to the line frequency of the television. A suitable means insures resynchronization of the sampling clock at the middle of each line.

Abstract: A 70.+-..DELTA.f MHz sinusoidal test signal from a standard radio link test set is down converted and shaped to obtain a 35.+-..DELTA.f/2 MHz sinusoidal test signal to be applied to the radio set under test. The output of the radio set is applied to an up converter in which a multiplier is used that maintains the amplitude information as it doubles the frequency. The 70.+-..DELTA.f MHz test signal from the up converter is then applied to the input of the radio link test set, and the characteristic is measured as if the radio set under test employed a 70 MHz IF, rather than a 35 MHz IF.

Abstract: An ultrasonic communication system capable of wireless installation and supervised operation is achieved by communicating each information bit as two distinct ultrasonic frequencies separated in frequency enough to assure that the signal strength of both transmissions will not be in a deep null at the receiver location at the same time. The transmissions can be coded with a format that recognizes the correct data transmission even if reception of one frequency is lost. By use of transponders and other auxiliary units with periodic polling, supervised operation throughout a building can be maintained with events such as intrusion, fire or emergency as well as failures of particular units of the system reported.

Abstract: A surveillance system transmits a microwave carrier signal through a surveillance zone (14). Two low frequency energy fields are also established in the zone being produced by respective pairs of closely spaced apart low frequency signals radiated from opposite sides of the zone. A receptor reradiator in the zones receives these signals and reradiates a reply signal to a receiver the reply signal consisting of the microwave carrier signal amplitude modulated in accordance with the instantaneous value of the low frequency fields at the location of the receptor reradiator. The receiver separates out preselected intermodulation products and activates an alarm only when the preselected intermodulation products are present.