Abstract: In an adaptive filter (56) the coefficients of a transversal filter (64) are adjusted by a processing circuit (78) to reduce the difference between a signal applied to the filter input (55) and a reference signal applied to a further input (57) so that the filter transfer characteristic becomes such that it will convert a first signal into a second signal. The first and second signals are constituted by a signal occurring in a signal path through a communications receiver and an ideal version of this signal respectively. In order that a relatively simple but hence relatively slow algorithm can be employed by the processing circuit without requiring a correspondingly long first signal the first and second signals are not applied to the adaptive filter directly but only after convolution in respective transversal filters (49,62) with the output of a noise source (60). The adaptive filter is then used as an equalizer in the receiver.

Abstract: A switching system is described in which routing information, which may be associated with packets originating in cellular calls, is divided into information which does not change as the subscriber crosses a cell boundary, and information which does change as the subscriber crosses a cell boundary. Routing procedures associated with the information which does not change as the subscriber crosses a cell boundary are established and stored in the memory of the switch at the beginning of the call. However, routing procedures associated with the information which does change as the subscriber crosses a cell boundary may be derived from the header information of each packet as it arrives at the appropriate portion of the switch.

Abstract: An alarm system, particularly a radio transmitter alarm system in which an alarm condition causes the propulsion of an alerting radio transmitter to a high altitude, thereby significantly increasing the reliable working distance between a protected location and a staffed, alarm-receiving point.

Abstract: The present invention relates to a majority logic spread spectrum, FH-MFSK radio receiver capable of demodulating and decoding one or more concurrently received L-length frequency-hopping, 2.sup.K -ary frequency shift keyed signals to determine the correct signal of a particular user. In operation, the receiver spectrum-analyzes the received signal to determine which frequency components are present during each of the L chip intervals and then modulates a particular user's L-length FH address signal with the derived frequency components to arrive at a 2.sup.K by L-length detection matrix. A majority logic decision circuit determines the level having the maximum number of derived frequency components along the L-length axis of the matrix, or which is the most likely level of multiple equal levels, and decodes the chosen 2.sup.K level into the indicated message signal.

Abstract: A broad band antenna suitable for mounting on a ground plane comprises a pair of spaced-apart, linear hollow monopoles perpendicular to the ground plane and an air-dielectric coaxial transmission line extending linearly between the monopoles parallel to the ground plane. Means are provided grounding the outer conductor of the transmission line to the ground plane, the inner conductor top-connecting the monopoles.

Abstract: An antenna consisting of three separate members, two members which are oriented perpendicular to a ground plane which function as short monopole antennas and a third member parallel to and above the ground plane which functions as a single conductor transmission line above ground, top-connecting the two antennas. One of the monopole antennas is connected to the ground plane through a terminating resistor and the other monopole is connected to the ground plane through an impedance matching transformer. The antennas mount on a ground plane, an electrically conducting surface such as the roof of a vehicle, aircraft or other suitable surface, and take an aerodynamic shape. The antenna exhibits a cardioidal pattern over an azimuth angle of approximately 120.degree. and is especially applicable for use in a multiple antenna arrangement in the application of direction finding systems. The antenna is useful over a wide range of frequencies without adjustment, because of its broad bandwidth, which exceeds 100:1.