Abstract: The potential threat to digital radio baseband equipment from excessive currents in an electrical communication cable, due to a lightning strike at or near the top of an RF transceiver tower is avoided by replacing the electrical cable with a non-electrical signaling path, in particular a fiber optic signaling path. Power for the RF transceiver is conveyed to the tower in a separate electrical link. This serves to effectively electrically isolate baseband equipment from a potential source of potential lightning strikes, while at the same time providing full intra-communication connectivity within the digital radio.

Abstract: An improved isolation circuit for protecting data communication equipment from high voltages on a transmission line has two mixers. The first dual balanced mixer (DBMX) translates a data signal on the transmission line to a high frequency and is coupled with an isolation circuit to the second DBMX. The second DBMX then translates the output of the first DBMX to an isolated data signal with the same frequency content as the original data signal.

Abstract: In a digital data communications device for use in an ISDN environment, a power supply apparatus and method are provided for energizing telephone danger circuitry or other alerting mechanisms. Embodiments of the present invention employ signal generators which control switching circuitry that converts a low voltage DC power source into a low voltage alternating current. A step-up transformer is used to convert or transform this low voltage into a high voltage alternating current, which is rectified and filtered to generate a high voltage direct current. The signal generators also control the switching circuitry which applies this high voltage direct current to an alerting mechanism and alternately provides a path to discharge energy which may be stored in the alerting mechanism, causing the alerting mechanism or other ringer circuitry to resound.

Abstract: A buck-topology switching power supply (100) combines a plurality, n, of signals (111, 121, 131) from a like number (n) of substantially direct-current power sources by means of a single inductor (150). As k varies from 1 to n, a controller (170) acts to couple each signal.sub.k in sequence to the inductor input (140) for an"on" duty period t.sub.k at a predetermined switching frequency, f, thus forming at the inductor output (160) an output signal having an output voltage V.sub.o and an output power P.sub.o. Under static load conditions, the controller holds the corresponding duty period t.sub.k for each signal.sub.k at a substantially constant value. Under dynamic load conditions, however, the controller dynamically adjusts the corresponding duty period t.sub.k in order to maintain the fractional power contribution P.sub.k for each signal.sub.k relative to the output power P.sub.o at a predetermined value.

Abstract: An equalizer (100) is suitable for removing the delay distortion from a switched digital signal received from a telephone channel, where the delay distortion is caused by a bridge-tap connected to the telephone channel. The equalizer includes a feedback delay circuit (200) which is arranged to delay the output signal (150) by an amount of time based on the square of the predominant frequency of the output signal. The resulting delayed feedback signal (130) is then combined with the input signal, thereby compensating for the delay distortion. The equalizer also includes an amplifier (103) which may be adjusted to compensate for the attenuation distortion caused by the bridge-tap.