Abstract: A probe in a hand held ultrasonic Doppler fetal heart beat detector and monitoring system comprising a crystal for transmitting ultrasonic energy, a variable power source connected to said crystal for driving the crystal at a selected power setting and a microprocessor for selecting a power setting for the variable power source.

Abstract: A noise controller for use in a probe in a hand held ultrasonic Doppler fetal heart beat detection and monitoring system where the probe includes a crystal for generating an input signal as a function of the ultrasonic energy in received ultrasonic wave and a detector for generating a first signal from the input signal. The noise controller comprises a volume controller for receiving the first signal and for processing the first signal to produce an analog signal as the output of the probe. A detector generates a second signal whenever break noise is detected in the first signal. A muting circuit immediately lowers the amplitude of the analog signal upon detection of break noise by the detector thereby substantially attenuated in the analog signal the break noise which occurred in the first signal.

Abstract: A cellular telephone system is described of the type wherein a plurality of contiguous cells, each having an assigned set of identification codes, are arranged with means for maintaining continuous communication with mobile telephones moving from cell to cell. The system allows multiple access by including means for assigning at least one of the in the assigned set of identification codes to more than one mobile telephone. A unique identification code is assigned to a mobile telephone located in the cell. A signal having a unique identification code is generated for identifying the mobile telephone. The signal is coupled to the zones. A combiner is also provided for combining signals from all of the zones in the cell. A receiver is coupled to the combiner for retrieving the signals having the code.

Abstract: An Inbuilding Communications System for providing telephone communication to a first set of portable telephones located in a first area and to a second set of portable telephones located in a second area; the first set of portable telephones transmit and receive a first set of radio signals having a set of assigned frequencies; the second set of portable telephones transmit and receive a second set of signals having the same set of assigned frequencies; the first and second areas are separated by a structure which attenuates radio signals. A first set of at least two antennas is located inside the first area for communicating with the first set of portable telephones. The number of antennas and the position of each antenna in the first set of antennas are chosen such that the first set of radio signals is attenuated below a pre-determined level after passing through the structure.

Abstract: A cellular telephone system is described of the type wherein a plurality of contiguous cells, each having a different assigned set of transmission frequency channels, are arranged with handoff control for maintaining continuous communication with mobile telephones moving from cell to cell. The system allows multiple access by including assigning at least one of the frequencies in the assigned set of transmission frequencies to more than one mobile telephone. Three embodiments of the multiple access systems are disclosed. In one embodiment, a frequency division multiple access is used. In a second embodiment, a time division multiple access is used. In a third embodiment, a code division multiple access is used.

Abstract: An improved microcell system for cellular telephone systems has a plurality of contiguous cells wherein the cells are configured in a plurality of clusters with each cell in a cluster having a different assigned set of transmission frequencies. Each of the frequencies in an assigned set for a given cell is assignable to a given mobile telephone within the cell for all locations of the mobile telephone within the cell. Frequency handoff circuitry is provided for maintaining continuous communication with mobile telephones moving from cell to cell. Each of the cells is provided with a plurality of antennas each of which is arranged and configured to limit propagation of signals substantially to one of a plurality of regions within the boundaries of the cell, which regions are substantially less in area than the area of the cell.

Abstract: A communications system utilizes artificial intelligence to select connectivity paths among various locations in a communications network. An embodiment shown is that of a packet radio network, wherein an artificial intelligence module, located at one or more of the radio sites in the network, applies a set of heuristic rules to a knowledge base obtained from network experience to select connectivity paths through the network. The artificial intelligence module comprises an inference engine, a memory for storing network data obtained from a radio receiver and transmitting it to the inference engine, a memory connected to the inference engine which stores a set of heuristic rules for the artificial intelligence system, and a knowledge base memory which stores network information upon which the inference engine draws. The knowledge base memory is also capable of feeding back network information to the rule base memory, which can thus update its rules.

Abstract: A door activity monitoring apparatus (10) including a pivoted signal unit (11) that is mounted on a door jamb (100) and has a magnetically attractive indicator member (14) which cooperates with a magnetic keeper unit (12) that is secured to the door (103) to provide a visual signal indicative that the door (103) has been moved relative to the door jamb (100).

Abstract: A cellular telephone system is described of the type wherein a plurality of contiguous cells, each having a different assigned set of transmission frequency channels, are arranged with handoff circuitry for maintaining continuous communication with mobile telephones moving from cell to cell. The system includes at least one cell having a plurality of transmitting and receiving antenna sets. Each set is positioned at a respective antenna sub-site at the perpihery of the cell or other suitable location, and is configured so that propagation and reception of signals is limited to substantially within the boundaries of the cell. Control circuitry monitor the strength of the signal received by each of the antenna sets at each frequency channel in the assigned set. Transmission, at each frequency channel in the assigned set, is confined to the antenna set at one sub-site in the cell having the strongest received signal at each frequency.

Abstract: The field component diversity antenna and receiver arrangement comprises at least a first pair of parallel spaced, straight, vertical elemental antenna elements disposed substantially parallel to the electric field component of a transmitted signal to receive the transmitted signal in a multipath fading environment where the electric field and magnetic field components are uncorrelated and a 180.degree. hybrid circuit coupled to the first pair of spaced antenna elements to provide a first output signal proportional to the electric field components and a second output signal proportional to the magnetic field component. The spaced elemental antenna elements may be monopole elements or dipole elements. The pair of antenna element may be connected together by a straight conductor to enhance the magnetic field component. The first and second output signals may be combined by known diversity combining arrangement to achieve a diversity advantage.

Abstract: The covert communication system comprises a first arrangement to translate binary "1" bits into different portions of a predetermined PN (pseudonoise) code sequence and primary "0" bits into a complement of the different portion of the PN sequences, the PN sequence being selected to spread the binary signal over as large a bandwidth as possible. A second arrangement is coupled to the first arrangement to transmit the portions of the PN sequence and the complements of the portions of the PN sequence at a variable transmission rate and at a power level below environmental noise of propagation medium. A third arrangement is coupled to the second arrangement through the propagation medium to receive the portions of the PN sequence and the complements of the portions of the PN sequence imbedded the environmental noise with a fourth arrangement coupled to the third arrangement to recover the binary signal from the received portions of the PN sequence and the received complements of the portions of the PN sequence.

Abstract: In cellular mobile radiotelephone systems employing reuse of a predetermined set of channels in adjacent iterations of a pattern of cells (FIG. 1), average signal-to-interference ratio in at least one cell region of interest is improved by tilting the antenna (11,12) gain pattern center-beam line of an antenna serving that region below the horizontal (FIG. 3). In one embodiment the tilt (.theta.) is sufficient to create a reduced-gain notch (FIG. 8) in the center-beam portion of the pattern.