Abstract: A system for testing protection against spurious response interference in a radio receiver by imposing wide band interference signals. An interference generator (210) produces a wideband interference signal (220). This interference signal (220) is combined with a test signal (215) generated by a channel generator (205). This combined signal is received by the unit under test (235). The unit under test (235) is insensitive to the interference signal (220) and receives the result signal (240). The result signal (240) is compared to the test signal (215) to check for reception errors. If errors are detected, the wideband interference signal (220) is subdivided and retested in an iterative manner until the band is small enough to perform single frequency tests to locate the frequency causing the error.

Abstract: A transceiver (10) having a retractable antenna (12) that substantially reduces interference when the antenna is in a retracted position. The transceiver (10) includes transceiver circuitry (T), operating at a predetermined frequency, electrically connected to the retractable antenna (12). The retractable antenna (12) includes two antenna elements (20, 22). A first antenna element (20) comprises a whip antenna element, movable within a conductive tube (14) housed within a cellular telephone case (C). A second antenna element (22) comprises a helical coil antenna element extending from the whip antenna element (20) and located outside the case (C). In the retracted position, a first contact assembly (76) contacts the whip antenna element (20). The first contact assembly (76) is electrically connected to the transceiver circuitry (T) through a conductor (96) which is a predetermined multiple of a quarter wavelength at the predetermined frequency.

Abstract: A tunable filter (25) is described for use in loop control circuits. The filter (25) has a time constant which is determined by a resistor (40) and a capacitor. The capacitor is simulated by the series combination of an impedance converter (41) and a variable resistor, such as a field effect transistor (42). The resistance of the transistor (42) is determined by a control signal present on a control line (32) and the impedance converter (41) converts the resistance into an equivalent capacitive reactance. Therefore, the control signal on the control line (32) effectively controls the capacitance present at a node (43) and, in conjunction with the resistor (40), determines the time constant, and therefore the response time and bandwidth, of the filter (25). Multiple pole, lowpass, bandpass, highpass, and bandstop filters can be constructed. The impedance converter (41) uses a very small capacitor to simulate a large capacitance value at the node (43).

Abstract: A car radiotelephone system having one or more wireless handsets communicating voice and control information via an ultrasonic link with a stationary unit connected functionally to a base station. The base unit (1) is connected by two cables, an audio-out cable (a) connected to the radio frequency receiver (2) and an audio-in cable (b) connected to the radio frequency transmitter (3), to a stationary transmitting/receiving unit (4). The stationary transmitting/receiving unit consists of two summing amplifiers, transmitting summing amplifier (5) and receiving summing amplifier (6), and any number of ultrasonic transmitters and receivers. Likewise, any number of handsets can be used. The handsets (15) comprise an ultrasonic receiver (19), an ultrasonic transmitter (20), transmitter and receiver circuitry (27), a keypad (28), display circuitry (29), microphone (30), earpiece/speaker (31), and a rechargeable battery and ringer.

Abstract: An impedance matching transformer includes a dielectric having a varying thickness between opposing surfaces. A transmission conductor and a return conductor are formed on the opposing surfaces. The impedance transformation between a first terminal and a second terminal is proportional to the thickness variation of the dielectric.

Abstract: A network (10) for matching impedance from a first transmission line (14) to a second transmission line (16) includes a dielectric material (12, 20), a conductor (24, 26, 28), and metalization (18, 30) located on at least some portions of at least one outer surface of the dielectric material. The area covered by the metalization gradually diminishes from the first transmission line to the second transmission line. The conductor provides an electrical connection between the first transmission line and the second transmission line. The conductor provides an electrical connection between the first transmission line and the second transmission line, and is located at least partially within the dielectric material.