A diversity receiver includes first and second antennae for receiving an RF signal, and an antenna switching circuit for selecting one of the first and second antennae. A first detection circuit having a high sensitivity, and a second detection circuit having a low sensitivity are provided, each detecting a noise signal contained within the received RF signal in different sensitivity. A field strength detection circuit is provided for detecting a field strength of the received RF signal, and a selection circuit is provided for selecting either one of the first and second detection circuits according to the output signal of the field strength detection circuit, and for providing a switching signal to the antenna switching circuit. Thus, when the field strength is relatively strong, the first detection circuit with high sensitivity is used for the noise detection, and when the field strength is relatively weak, the second detection circuit with low sensitivity is used for the noise detection.
An apparatus and method for detecting an antenna mispointing condition of an earth station. A noise floor detector, coupled to a received radio communications link signal, measures a noise floor of a selected frequency band in which no radio signals are normally present. A controller, coupled to the noise detector, detects an antenna mispointing condition when a signal strength of the received radio communications link signal is less than a predetermined signal strength and a difference between the measured noise floor and a baseline noise floor measurement is less than a predetermined difference.
An object of the invention is to provide an FM radio receiver capable of improving the receiving state. The radio receiver 10 is disposed within a vehicle room and provided with a vehicle-mounted antenna connection terminal 12. The radio receiver 10 includes a front-end unit converting to an intermediate frequency signal an FM broadcast signal received via a vehicle-mounted antenna 110, a signal line inserted between the vehicle-mounted antenna connection terminal 12 and the front-end unit, and an in-vehicle antenna 14 branching out from the signal line. A radio wave transmitted from an FM transmitter 40 disposed within the vehicle room via an antenna 42 is received by the radio receiver 10 via the in-vehicle antenna 14.
A emergency communication device which performs self diagnosing by repeatedly transmitting a weak signal, which can only be received by an antenna, among a plurality of antennas in a fixed time interval. When the weak signal is not received due to the occurrence of an accident, theft or the like, the occurrence of the emergency is communicated to an emergency data receiving center.
An interference cancellation circuit which can remove the interference signal caused by other systems and contained in received signals. The interference signal can be cancelled even if the interference signal is not directly obtained or plural interference signals exist, or the interference signal is a wide band signal or raster interference simply by receiving two signals which have passed through different transmission paths, combining the main signals contained in each of the received signals in a manner to offset each other to the extract interference signal, and removing the interference signal component from the received signal based on the expected interference signal.
An apparatus comprising a Viterbi decoder which decodes received convolutional code data in accordance with the Viterbi algorithm and provides path metrics. Among the path metrics, a path metric comparator detects the maximum and minimum path metrics for each data symbol. The path metric comparator selects the minimum difference among differences between the maximum and minimum path metrics. An apparatus also comprises a field strength detector which detects the electromagnetic field strength of a radio signal containing the convolutional code data. Upon the minimum path metric difference and the field strength, an interference detector checks if interference exists in the radio signal. The minimum path metric difference may be used for an antenna diversity system.
