Abstract: A transmission system for transmitting data over a channel in the form of a digital signal comprising bits of data, the system comprising an encoder for encoding the data prior to transmission, the encoder producing coding in the form of an overhead, and a decoder for decoding the data after transmission, characterised in that a first portion only of the data is encoded, the second portion remaining uncoded, the system further comprising a partitioner for partitioning the overhead from the uncoded data portion of the signal, after the first portion data has been encoded.

Abstract: A wavelength division multiplexing transmission system, the system comprising: a plurality of channels at different wavelengths, each channel comprising a transmitter, a receiver, and one or more amplifiers, the system further comprising an encoder for encoding data with a coding, and; a decoder for decoding transmitted data; prioritizing means for prioritizing the data on each channel; monitoring means for monitoring directly or indirectly, raw (uncorrected) bit errors on each channel; power adjusting means for, varying the power on a channel in response to the bit error rate.

Abstract: A wavelength division multiplexing transmission system, the system comprising: a plurality of channels at different wavelengths, each channel comprising a transmitter, a receiver, and one or more amplifiers, the system further comprising an encoder for encoding data with a coding, and; a decoder for decoding transmitted data; prioritizing means for prioritizing the data on each channel; monitoring means for monitoring directly or indirectly, raw (uncorrected) bit errors on each channel; power adjusting means for, varying the power on a channel in response to the bit error rate.

Abstract: A wavelength division multiplexing transmission system, the system comprising: a plurality of channels at different wavelengths, each channel comprising a transmitter, a receiver, and one or more amplifiers, the system further comprising an encoder for encoding data with a coding, and; a decoder for decoding transmitted data; prioritizing means for prioritizing the data on each channel; monitoring means for monitoring directly or indirectly, raw (uncorrected) bit errors on each channel; power adjusting means for, varying the power on a channel in response to the bit error rate.

Abstract: An optical communications system comprising: an optical input and an output, a source of input signals in an asymmetric format and having a duty cycle, a modulator for modulating the input signals, to produce an asymmetric signal, the modulator comprising a Mach-Zehnder interferometer; drive means for driving the modulator at a predetermined modulator drive voltage; bias means for applying a bias voltage to the modulator; adjustment means for adjusting a first variable chosen from one of the bias voltage, gain voltage, or duty cycle in response to the relationship existing between changes in the amplitude of the asymmetric signal and changes in the first variable, characterized in that the system further comprising varying means for varying a second variable, different to the first variable and chosen from one of the bias voltage, gain voltage or duty cycle in response to adjustments made to the first variable; and a monitor for recording the average optical output power.

Abstract: A method of locating a submarine cable includes the steps of transmitting a toning signal along the submarine cable, the toning signal being a superposition of a first signal waveform to be detected and at least a second signal waveform such that the second signal waveform interferes with the first signal waveform to limit the peak to peak amplitude of the toning signal for transmission. Preferably, the toning signal is a square wave. The method provides a way of offsetting the loss of transmission distance due to the use of state of the art optical repeaters. Pre-emphasis of high frequency harmonics in the toning signal enables a detectable toning signal to propagate still further.

Abstract: An air filter element for internal combustion engines includes a filter media having an inlet portion and an outlet portion positioned adjacent to one another, so that a single filter element may be used with an air filter assembly; the filter element having an inlet and an outlet openings in the same direction. The inlet and outlet portions of the filter element are sealed with a housing by a common peripheral gasket.

Abstract: A roof for the cab of vehicle is constructed with a hollow plastic body that is molded in one piece with a blower and a heat exchanger fitted to the hollow body. The hollow body defines a cavity that forms an air duct through which air for ventilating the cab is ducted. Shuttered external and internal air intake vents allow the selection between fresh air from externally of the cab and recirculated air from within the cab. A well open through the roof provides an emergency exit from the vehicle cab.

Abstract: A branching unit for use in submarine telecommunications optical cable systems which employs electrical power feeding for repeater/regenerators of the cable system, in particular a system employing multiple branching units. The unit terminates three line cables (at 1, 2, 3) and a sea earth (at 4) and includes first, second the third high voltage relays (A, A1, B, B1, C, C1), only one of which is energized at a time. When electrical power is supplied between any two line terminations, e.g. 1 and 3, an associated relay coil, e.g. C is energized so that its contacts C1 isolate the third line termination, e.g. 2, and connect it to the sea earth termination (4) via fourth, or fifth, relay contacts (D1, E1 ). The branching unit also includes a plurality of optical regenerators, for optical path switching purposes, which require electrical power feeding and whose power feed circuits 20 are connected in parallel with each of the relay coils. When any relay is energized, i.e.

Abstract: A branching unit for use in a submarine telecommunications cable system which employs electrical power feeding for repeaters/regenerators and in particular a system employing multiple branching units. The unit terminates three line cables (at 1, 2, 3) and a sea earth (at 4) and includes three high voltage element relays (A, A1; B, B1; C, C1) only one of which is energized at a time. When electrical power is supplied between any two line cables the third is isolated and connected to the sea earth. Short circuit or open circuit faults in one line cable may be isolated and connected to the sea earth, whilst allowing powering of the remaining fault free two line cables. The unit is polarity insensitive and symmetrical, cathodic protection being provided on all three lines (FIG. 1).