Abstract: A communication system is enclosed. In one embodiment, the communication system includes a communication device configured to puts itself into an activated state or into a deactivated state at alternate times. The communication device receives time information in a first operating state of the activated state, takes the received time information as a basis for ascertaining the later time at which useful information is transmitted to the communication device, receives the useful information at the later time in a second operating state of the activated state, and with individual components of the communication device being able to be put into an activated state or into a deactivated state independently of one another.

Abstract: A plurality of modules interact to form an adaptive network in which each module transmits and receives data signals indicative of physical properties sensed at the modules. A new module is joined in the adaptive network in an expedient manner. The new module transmits a burst of beacon messages after the interactive module is activated to discover neighboring interactive modules deployed and operating in the adaptive network. The neighboring interactive module stays in a sleep-mode of low-power expenditure. The beacon messages persist for a first interval longer than a second interval during which the neighboring interactive modules remain in the sleep mode. After receiving the beacon messages, one or more neighboring interactive modules transmit response messages to the new interactive module. The new interactive module receives the response messages and selects a neighboring interactive module for communication based on the received response messages.

Abstract: A method, apparatus, and computer program product for processing health management data for a vehicle. A plurality of modulated signals is received on a bus system in the vehicle. The plurality of modulated signals contains health management data from a plurality of data acquisition units. Each modulated signal has a different frequency from another modulated signal in the plurality of modulated signals to form a plurality of frequencies. The plurality of frequencies is selected to avoid interference with other data transmitted over the bus system by a plurality of data processing systems in the vehicle. The plurality of modulated signals is processed based on the plurality of frequencies used to transmit the plurality of modulated signals.

Abstract: RFID tags, such as those in boluses for ruminant animals, comprise RFID tags may be provided with energy harvesting (EH) capability so that they may collect energy from the environment, either deliberately radiated (such as RF) or gathered from existing sources (i.e., motion, heat, etc.). The energy collected by the RFID tag allows for independent (stand-alone) operation of the tag, such as for logging of temperature in one hour intervals, then transmitting the temperature readings (and ID) periodically (such as six times per day) to a reader (or equivalent, such as an active receiver) using an active RF transmitter (radio) or passive RFID techniques.

Abstract: A tag includes a processor, a radio frequency transmitter coupled to the processor, and a capacitively driven communication circuitry coupled to the processor. The processor is to energize the capacitively driven communication circuitry to receive a serial set of binary bits via the capacitively driven communication circuitry.

Abstract: A multi-band and/or multi-protocol, configurable, RFID tag is provided. The tag can include one or more electrical or mechanical selectors for selecting from among multiple frequency bands and communication protocols. In some embodiments, a signal band and protocol can be detected automatically and selection among bands and protocols can be performed automatically. In some embodiments, one or more externally accessibly switches can be actuated by a user to select a band and/or protocol.

Abstract: An implantable medical device having a transceiver for transmitting/receiving wirelessly transmitted data, which is turned off or switched into an energy-saving rest state between individual data transmissions via the transceiver and having a waking unit which is implemented to switch the transceiver by a waking signal from its turned-off state or its rest state into its fully operational state, the waking unit having a low-power receiver and a waking control unit of which the low-power receiver is implemented to monitor multiple predefined frequency ranges in such a way that in case of a transmission of sufficient signal strength in one of the frequency ranges, it generates an output signal and outputs it to the waking control unit and of which the waking control unit is implemented to analyze output signals of the low-power receiver and output a waking signal to the transceiver which switches it on or to fully operational.

Abstract: A technique for re-acquiring a symbol index in the presence of sleep timer errors in a MediaFLO™ (Forward Link Only) mobile multimedia multicast system comprising a receiver and a transmitter, wherein the method comprises receiving a digital signal comprising a superframe comprising one or more Orthogonal Frequency Division Multiplexing (OFDM) symbols in the receiver comprising a timer; waking up the receiver from a sleep mode of operation by an amount of time equal to a maximum error introduced by the timer plus a time to reacquire a beginning of each OFDM symbol plus a time to reacquire a symbol index; and reacquiring the symbol index.

Abstract: A method of forming ad hoc RSI hierarchical communication networks among pluralities of wireless transceivers includes assigning to each of the transceivers one or more common designations. A network organization routine of the transceivers operates to establish hierarchical networks based on the transceivers' common designations, resulting in a logical network organization that provides efficiencies for acquiring information from particular transceivers that share a common designation. Each transceiver's common designation is used by a digital processor of the transceiver to selectively receive data packets that are intended for receipt by transceivers sharing the particular common designation. Such a “common designation” network reduces power consumption and signal interference thereby increasing battery life.

Abstract: A method of forming ad hoc RSI hierarchical communication networks among pluralities of wireless transceivers includes assigning to each of the transceivers one or more common designations. A network organization routine of the transceivers operates to establish hierarchical networks based on the transceivers' common designations, resulting in a logical network organization that provides efficiencies for acquiring information from particular transceivers that share a common designation. Each transceiver's common designation is used by a digital processor of the transceiver to selectively receive data packets that are intended for receipt by transceivers sharing the particular common designation. Such a “common designation” network reduces power consumption and signal interference thereby increasing battery life.

Abstract: A transponder that may be used as an RFID tag includes a passive circuit to eliminate the need for an “always on” active RF receiving element to anticipate a wake-up signal for the balance of the transponder electronics. This solution allows the entire active transponder to have all circuit elements in a sleep (standby) state, thus drastically extending battery life or other charge storage device life. Also, a wake-up solution that reduces total energy consumption of an active transponder system by allowing all non-addressed transponders to remain in a sleep (standby) state, thereby reducing total system or collection energy. Also, the transponder and wake-up solution are employed in an asset tracking system.

Abstract: Various example embodiments are disclosed herein. According to an example embodiment, a method may include generating, by a first wireless communication system, a first label based on performing one or more hash functions on at least information relating to data to be requested; storing the first label in a set of one or more active labels; transmitting a data request to request the data; transitioning at least a portion of the first wireless communication system from an operational state to a low power state; receiving a message including a second label; comparing the second label to the set of one or more active labels, each of the active labels associated with an outstanding data request; determining that the second label matches one of the one or more active labels based on the comparing; and waking up at least the portion of the first wireless data communication system from the low power state back to the operational state in response to the determining.

Abstract: A device including an RF transceiver coupled to receive signals from an antenna; and a micro-controller coupled to the RF transceiver periodically scanning for a wakeup signal and measuring a signal strength is provided. The micro-controller may use the signal strength to update a count value in a bin of a histogram. The micro-controller may also decrement histogram values periodically, and direct the RF transceiver to respond to the wakeup signal if the count value in the histogram is lower than a threshold value. Further according to some embodiments disclosed herein a system for avoiding over polling in wireless communications may include a tag and a reader. The reader may transmit a wakeup signal periodically and the tag may operate as the device disclosed above. Also, a method for using a device and a system as above is provided.

Abstract: A communication system with a plurality of devices with a communication unit (CU1) arranged to communicate on a first wireless communication channel (CH1), e.g. GSM, in an active mode. Otherwise, the communication unit (CU1) is in an in-active power saving mode. A receiver unit (R1, R2) receives a wake-up signal on a second wireless communication channel (CH2, CH3), e.g. RFID. The receiver unit (R1, R2) then switches the communication unit (CU1) into active mode. The second wireless communication channel (CH2, CH3) is dedicated for wake-up signals and is in a different frequency band than the first wireless communication channel (CH1). Further, the first wireless communication channel (CH1) has a larger distance range than the second wireless communication channel (CH2, CH3).

Abstract: A transceiver comprising a transmit pin configured to receive a signal from a microcontroller, a receive pin configured to transmit a signal to a microcontroller and a bus pin configured to transmit and receive signalling to/from a network.

Abstract: A RF data communication device operates in at least two states. In a first state, the device transmits a response to an RF transmission if specific data therein represents an inquiry as to the presence of one or more RF data communication devices and if specific data therein corresponds to a class maintained by the device. The device does not transmit a response if specific data in the RF transmission is not representative of an inquiry as to the presence of one or more RF data communication devices, or if specific data therein does not correspond to at least one maintained class. In a second state, the device does not transmit a response when specific data is included therein that is representative of an inquiry as to the presence of one or more RF data communication devices and specific data therein corresponds to at least one maintained class.

Abstract: Methods and apparatus are disclosed for location of objects to facilitate retrieval, filing, security, inventory stock-keeping and the like. The methods and apparatus employ a tag element associated with each object-to-be-located, an interrogation system for searching one or more spatial regions for such tagged items, as well as mechanisms for identifying objects within the interrogated region.

Abstract: A plurality of wireless transceivers are associated with assets and each transceiver is assigned a class designation representative of an attribute, characteristic, relation, or behavior of its respective asset. Class based network formation routines are utilized to establish hierarchical networks based on asset classes, and the asset class is used by each transceiver to screen communications intended for receipt by transceivers of the same class. The overall wireless data communication network results in reduced power consumption and signal interference in asset tracking applications. The transceivers may include a query handling routine for forming a dynamically distributed hierarchical database system.

Abstract: Embodiments include a main host system of the client computer, and a network event notification system, including a networking subsystem that communicates with a network server to act as a proxy for the client computer when the main host system of the client computer is in a sleep state. The networking subsystem awaits a synchronization packet initiated by the network server, or polls the network server to determine whether data is available. The computing device operates an associated network subsystem while the main host system of the computing device is in a sleep state, and receives data via the network subsystem indicating that content is available to the computing device. Policy is then invoked to determine whether to wake at least part of the main host system to handle the content. A target duty cycle mechanism is also provided to control the average power consumption during wake and sleep cycling.

Abstract: The invention relates to a method for the operation of an RFID transponder, which is characterized by the fact that the RFID transponder is operated either in broadcast mode or in bidirectional response mode or simultaneously in both aforementioned modes. The RFID transporter is equipped with a wireless transmitter as well as with a wireless transmission/reception unit for operation in these two modes, said wireless transmitter and wireless transmission/reception unit being operable independently from one another.

Abstract: Provided are telecommunications devices and systems which incorporate and use radio frequency (RF) tag technology. Telecommunications devices in accordance with one embodiment of the present invention incorporate RF transceivers (readers) which are configured to read associated RF transponders (tags) in order to automatically dial desired telephone numbers without the need for a manual user interface. Tags in systems in accordance with this embodiment of the present invention may be attached to or incorporated with a myriad of items, including picture frames, consumer products and packaging, advertising and promotional material, electronic business cards, record-keeping systems, etc. Devices and systems in accordance with the present invention have a variety of telephony and non-telephony applications.

Abstract: Remote communication devices, radio frequency identification devices, wireless communication systems, wireless communication methods, radio frequency identification device communication methods, and methods of forming a remote intelligent communication device are provided. According to one aspect, a remote intelligent communication device includes communication circuitry configured to at least one of receive communication signals and generate communication signals; and an antenna coupled with the communication circuitry and substantially tuned to a plurality of frequencies, the antenna being configured to communicate wireless signals corresponding to the communication signals including at least one of receiving wireless signals and outputting wireless signals.

Abstract: Communications device identification methods, communications methods, wireless communications readers, wireless communications systems, and articles of manufacture are described. In one aspect, a communications device identification method includes providing identification information regarding a group of wireless identification devices within a wireless communications range of a reader, using the provided identification information, selecting one of a plurality of different search procedures for identifying unidentified ones of the wireless identification devices within the wireless communications range, and identifying at least some of the unidentified ones of the wireless identification devices using the selected one of the search procedures.

Abstract: Vehicle including a switch assembly includes a vehicular component subject to control by an occupant in the passenger compartment, and a switch assembly for controlling the component based on pressure applied by the occupant of the vehicle to an exposed surface of the vehicle. The switch assembly includes at least one wireless transmission component arranged to wirelessly transmit an indication of the application of pressure to the exposed surface, and a control mechanism for controlling the wireless transmission by the wireless transmission component(s) based on the application of pressure to the exposed surface. The control mechanism may be a switch or a variable impedance which react to the application of pressure to the exposed surface.

Abstract: A wireless system suitable for use as a radio frequency (RF) locationing or presence detection system includes at least one wireless access device and at least wireless device, such as an active RF tag, corresponding to an item or asset of interest. A method of managing RF transmissions by the wireless devices is provided. The method involves the wireless device receiving keep-alive beacons during a first period of time. During this first period of time, the wireless device is operated in a transmit mode. During a second period of time that follows the first period of time, the wireless device receives no keep-alive beacons. During this second period of time, the wireless device is operated in a standby mode such that RF transmissions are disabled.

Abstract: An RFID reading system includes at least two readers and at least one RF tag. Each reader includes a transmitter, a receiver, and a CPU section to control transmission of the transmitter and reception of the receiver. Both readers receive a reply signal sent from an RF tag in response to a query wave sent from either one of the readers to the RF tag. The readers obtain tag information from the RF tag based on the received signals. To prevent interference therebetween, when one of the readers sends a query wave, transmission of a query wave from the other one thereof is stopped for a predetermined period of time. The information can be read without causing interference between the readers. There are obtained an RFID reading system, an RFID reading method, and RFID reader and a control program thereof, an RFID read control device and a control program thereof, and a computer-readable information recording medium storing the control programs.

Abstract: A quality control system of concrete and cement products is provided in which the manufacturing information on cement products of mortar or concrete can be checked at any time, the reliability is such that there is no possibility of the recorded information being lost or falsified, there is no possibility of damage in concrete, and the directivity of the sensitivity of an antenna can be broadened.

Abstract: A radio frequency identification (RFID) device includes an antenna configured to transmit or receive a radio frequency signal to or from an external communication apparatus; an analog block configured to generate a first power voltage in response to the radio frequency signal; a digital block configured to receive the first power voltage from the analog block, to transmit a response signal to the analog block, and to output a memory control signal; and a memory configured to read/write data in response to the memory control signal, the memory including a high voltage generating unit for generating a second power voltage from the first power voltage, a first portion driven by the second power voltage, and a second portion driven by the first power voltage, wherein the level of the first power voltage is lower than that of the second power voltage.

Abstract: A method, apparatus and system for radio frequency identification provides an on-off keyed amplitude-modulated illumination signal containing a sequence of bits configured to illuminate a radio frequency identification (RFID) tag, The illumination signal is received at the RFID tag, rectified to generate a wake signal for waking a processor which is subsequently powered by a battery. The received illumination signal is sampled and subjected to a thresholding process. Mobile telephone band interference is countered by correlating the sampled illumination signal to determine its bit sequence and then correlating the bit sequence against a predetermined key. An identification signal from the RFID tag is sent in response to a match.

Abstract: A method to remotely control a wireless unit, includes receiving an activation/deactivation request from a user. It is determined if the user is authorized to activate/deactivate the wireless unit. If the user is authorized to activate/deactivate the wireless unit, a signal is sent to the wireless unit causing the wireless unit to power-on/power-off in response to the signal.

Abstract: An arrangement of logically distinct wireless data communication networks share a gateway for communicating with external networks. Each logically distinct network preferably is a class-based network, the nodes of which include a wireless two-way radio frequency data communication device. Each device filter wireless communications received by it for an identification within the communication of its class designation, or for a class, abstract class, or subclass corresponding to its class designation; and process the communication if found and do not process the communication if not found. The gateway wirelessly communicates with each logically distinct network by including the respective class designation for the network with which the communications are desired. The other class based networks do not process messages that are communicated to the desired class-based network, thereby avoiding unnecessary power consumption by the wireless devices.

Abstract: An enhanced backscatter RF-ID tag reader system and multiprotocol RF tag reader system is provided. In a multiprotocol mode, the system emits a non-stationary interrogation signal, and decodes a phase modulated backscatter signal by detecting a stronger phase component from quadrature phase representations or determining phase transition edges in a phase of a received signal. The RF tag reader system predicts or follows the phase of the backscatter signal, thereby avoiding interference from nulls in the received signal waveform due to the non-stationary interrogation signal, relative movement or environmental effects. An acoustic RF-ID tag detection system detects the reradiated signal corresponding to respective transformation of a signal in the tag. Detection of either type of RF-ID tags therefore is possible, and the absence of any tag or absence of any valid tag also determined.

Abstract: In one embodiment of the present invention, a lock actuating device for a lock mechanism of a lock has a transceiver capable of interaction with a wireless key device, a controller coupled to the transceiver and capable of generating a control signal, and a lock actuator adapted for actuation of the lock mechanism upon receipt of the control signal from the controller. The controller has a sleep mode and an operational mode. The lock actuating device also has a wake-up arrangement including a sensor and associated circuitry. The sensor is positioned to detect the presence of a user in a vicinity of the lock actuating device. The circuitry is adapted to generate a wake-up control signal to the controller upon detection of the user, so as to cause the controller to switch from sleep mode to operational mode.

Abstract: A method recognizes whether a transponder designed for communicating with a communication station belongs to one of at least two groups of transponders. First, for each group of transponders, a check data block that is significant for the group of transponders is generated. Then, the data from the check data block that is significant for the group of transponders is evaluated for the recognition of whether the transponder belongs to the group of transponders.

Abstract: A wireless transceiver includes: (a) a low power radio frequency (LPRF) communications component capable of powering down to conserve energy and capable of powering up in response to an electronic signal, the LPRF communications component including a transmitter and a first receiver; and (b) a second receiver that is configured to screen a radio frequency broadcast and provide, on the basis of specific data identified therein, the electronic signal to the LPRF communications component in order to power up the LPRF communications component. The second receiver is adapted to draw less current than the LPRF communications component while awaiting receipt of and listening for a radio frequency broadcast.

Abstract: Processes to achieve low power discovery and wake-up in the presence of desired 802.11 coverage are disclosed. In one aspect, probabilistic scanning for 802.11 SSID triggers is provided. In another aspect, the 802.11 Access Point (AP) is equipped with a Bluetooth inquiring device, which initiates the wake-up process with a special inquiry access code (IAC). The special IAC can comprise the AP's 802.11 channel. Additional optional sensors (GPS, Gyroscope, odometer, etc) are provided such that probabilistic scanning reduces power consumption and improves the likelihood that an 802.11 channel scan will find a desired SSID. A Bluetooth inquiry allows a discovery process to either wake-up immediately, or ascertain the need for host wake-up by exchanging further information with the AP. Probabilistic scanning allows the use of sensors and historical or pre-loaded information to improve the probability that 802.11 scanning is not required on individual channels, further driving down power needs.

Abstract: A sensor enhanced communication device (200) is provided with a wake mode, a standby mode and sleep mode. The sleep mode is a periodic occurrence within the standby mode which places a cluster of sensors and transducers (202) into a state of arousal in which the sensitivity of the transducers and sensors is increased while the sampling rate is decreased. Incremental learning can occur during the sleep mode as well as basic memory transfers. Since the cluster does not have to re-acquire information upon entering wake mode, the overall power efficiency is improved.

Abstract: Methods, systems, and apparatuses for detecting a reader signal strength in a radio frequency identification (RFID) tag is described. A tag is configured to monitor an attribute of a reader transmitted signal, such as the signal strength. The tag generates an indication of the signal attribute, and transmits the indication of the signal attribute to the reader.

Abstract: A method of utilizing RFID tags for jointly processing a task and an associated system are provided. The method includes causing a plurality of RFID tags to enter a ready state, causing the RFID tags to enter an accessible state in turn, transmitting the task to the RFID tags, utilizing the RFID tags to jointly process the task, and reading a result from the RFID tags having processed the task.

Abstract: A tag can switch between first and second modes of operation, and consumes less power in the first mode. In the second mode, the tag can receive wireless signals having successive first and second portions. If the tag identifies a repetitive pattern of the wireless signals, the tag ignores the second portions of the signals. Otherwise the tag receives the second portions. In another embodiment, while in the second mode, the tag can receive wireless signals having successive first, second and third portions. The tag switches between the first and second modes at one rate until it detects the first portion, and then switches at a higher rate until it detects the second portion, and then stays in the second mode and receives the third portion.

Abstract: A wearable data processing system includes a high power radio module and a low power radio module. The high power radio module may retrieve data from radio frequency identifier (RFID) tags. The low power radio module may transmit data to a base station data pertaining to the detected RFID tags. The low power radio module may also receive a power management signal from a gate radio. The gate radio may have an adjustable range. A power management engine in the wearable data processing system may determine whether the low power radio module is receiving the power management signal from the gate radio. The power management engine may also activate and deactivate the high power radio module, depending on whether the low power radio module is receiving the power management signal from the gate radio. Other embodiments are described and claimed.

Abstract: A mobile terminal includes a passive wireless receiver and a wireless transceiver. The passive wireless receiver receives a first activation signal from another mobile terminal, and transmits a second activation signal using power from the first activation signal. The wireless transceiver receives the second activation signal, and establishes a wireless connection with the other mobile terminal in response to receiving the second activation signal.

Abstract: A detector receiver circuit (2) for use as a wake-up detector for detecting an amplitude modulated carrier signal is described. The circuit (2) comprises: an antenna (4) for receiving the modulated carrier signal; a transistor (10), such as an FET, is connected to the antenna (4) and configured to operate as a detector of modulation of the carrier frequency. The circuit further comprises a resonator circuit (12-16) which is also connected to the transistor and configured such that the transistor (10) can simultaneously oscillate at substantially the modulation frequency; an oscillator quenching means (20) for periodically quenching oscillation of the transistor (10) and means (26, 28, 30) for sensing the characteristics of the build-up of oscillation to indicate the presence of a modulated carrier signal.

Abstract: A wireless tracking system and method for real-time location tracking of an extreme-temperature sterilizable object is disclosed herein. The system and method utilize a tag attached to the extreme-temperature sterilizable object which includes a housing, a processor, a temperature sensor and a transceiver. If an internal temperature of the tag is detected by the temperature sensor, the tag enters a sleep mode. The temperature sensor periodically activates to determine if the internal temperature of the tag is within an acceptable operating range.

Abstract: A wireless sensor network communication apparatus and method selectively using infrared and radio frequency communication. The wireless sensor network communication apparatus includes a first communicating unit, a second communication unit, and a wireless node processor. The first communicating unit wakens a neighboring node in a sleep mode and transmits/receives the woken node and sensor data. The second communicating unit transmits/receives the woken neighboring node and the sensor data. The wireless node processor is wakened from the sleep mode, wakens the neighboring node in the sleep mode, and transmits the sensor data with a minimum low power through one of the first and second communicating unit. Accordingly, the apparatus can perform the wireless sensor network communication with lower power compared to the case that communication is performed only by the radio frequency communication function.

Abstract: A Write Broadcast system and method uses a base station to write sent data to all or some selected number (sub group) of tags in a base station field simultaneously. By unselecting the tags that have been successfully written to, and requesting a response from the remaining tags in the field (or sub group), the system determines, by receiving a response to the request, that there are tags in the field (sub group) that were unsuccessfully written to. Another Write Broadcast signal is sent to these tags. The system is useful for quickly (simultaneously) “stamping” information on the tag memory of a large number of tags in the field of the base station.

Abstract: An alert system and apparatus for an emergency alert system is provided to disseminate emergency information to the public utilizing a universal paging system through a personal alert device such as a cellular telephone, pager, PDA or E-FOB. The alert system utilizes an emergency alert system signal from the NOAA alert system to broadcast the alert message to cellular devices in a specified alert area. The broadcast message provides information related to the alert level. The E-FOB may be a passive device which is activated by a NOAA alert signal and then listens for a cellular message. If the E-FOB is within the alert area, the E-FOB provides information to the user. If the E-FOB is not within the alert area, the E-FOB returns to a passive state.

Abstract: A system and method for selectively activating a device based on an activate command. A circuit, in low power mode, listens for an activate command. The activate command includes a preamplifer centering sequence, an interrupt signal, and an activate code. The circuit receives a signal that may or may not be an activate command, self-biases the signal based on the preamplifer centering in the preamp/gain control, then determines whether the interrupt signal is of the proper length in the interrupt circuit. If the interrupt is not the proper length, the process stops. If it is the proper length, the command is recognized as an activate command, and a data slicer compares the activate code to a prestored value. If the activate code matches the prestored value, the device is powered up. If they do not match, the device is not initiated.

Abstract: The invention relates to a method for recognizing identification media in the communication area of a write/read device functioning according to the principle of inductive coupling in the MHz range, wherein an antenna is used for transmitting and receiving HF signals, in addition to a circuit for transmitting HF signals with a standard transmitter power output and a logic circuit for evaluating communication between a write/read device and an identification medium. A short inquiry signal consisting of several fundamental components of the HF field and having a standard transmission power output is periodically transmitted via a transmission path and the antenna and a response signal is detected on the antenna. The response signal is compared to a reference signal and a communication signal is transmitted in order to recognize an identification medium in the event that the response signal is different from the reference signal.

Abstract: A multimode transceiver circuit comprises a four port coupler of a type which splits a signal applied to one port between two of the other ports. The split signals are phase shifted by a known amount. A first port of the coupler is for receiving a signal and for outputting a signal therefrom. A controllable oscillator is connected to a second port of the coupler and switchable impedances (Schottky diodes) are connected to the remaining ports. A controller is provided for controlling the operation of the oscillator and the impedances to determine the mode of operation of the circuit. In one mode of operation, the oscillator is inoperative and at least one of the impedances is switched to operate as a non-linear impedance such that the circuit detects amplitude modulation of the signal applied to the first port.