Abstract: A method of pre-distorting a signal of a satellite transmission link so as to offset later transmission of the signal during transmission across the satellite transmission link has a link including route Nyquist band pass filters in up and down links. The signal is passed through a cascade of identical pre-distorting stages each of which generates an approximation of the required pre-distortion. Each successive stage receives the approximation from the preceding stage so that errors in successive approximations converge towards zero.

Abstract: A satellite communication apparatus has a corrector for reducing distortion of a signal in a communication channel. The corrector is formed by a forward model representative of a pre-calculated estimate of non-linearity and group delay of the satellite transmission/reception channel from the input to the up sampler through to the output of the down sampler. The forward model may also comprise a model of magnitude response of a satellite input multiplexer filter and output multiplexer filter. Cascaded identical stages of the corrector may be provided so that distortion in the channel is successively reduced towards zero by each successive stage. An initial approximator which is substantially the inverse of the distorting function of the forward model may be provided.

Abstract: A method up-link fade control for a satellite not having AGC, includes the steps of determining characteristics for correcting channel non-linearity, each characteristic being determined for a different value of up-link fade. A signal representative of up-link fade is determined by a beacon receiver and the signal is associated with a correction characteristic for the up-link fade. The correction characteristic associated with the signal is applied to a corrector of a modulator such that the corrector changes the modulator characteristics to modify constellation parameters at a satellite receiver.

Abstract: A satellite communication apparatus has a corrector for reducing distortion of a signal in a communication channel. The corrector is formed by a forward model representative of a pre-calculated estimate of non-linearity and group delay of the satellite transmission/reception channel from the input to the up sampler through to the output of the down sampler. The forward model may also comprise a model of magnitude response of a satellite input multiplexer filter and output multiplexer filter. Cascaded identical stages of the corrector may be provided so that distortion in the channel is successively reduced towards zero by each successive stage. An initial approximator which is substantially the inverse of the distorting function of the forward model may be provided.

Abstract: A method up-link fade control for a satellite not having AGC, includes the steps of determining characteristics for correcting channel non-linearity, each characteristic being determined for a different value of up-link fade. A signal representative of up-link fade is determined by a beacon receiver and the signal is associated with a correction characteristic for the up-link fade. The correction characteristic associated with the signal is applied to a corrector of a modulator such that the corrector changes the modulator characteristics to modify constellation parameters at a satellite receiver.

Abstract: The invention concerns a method and apparatus to synthesize a frequency employing digital phase words to represent successive phase values. A digital dither signal generator is used to generate a succession of dither words which are summed with the phase words to form address words. The address words are used to address a store to convert the address words to waveform values. The periodic quantisation noise introduced by the digital process is made more random by means of the dither words thereby reducing the quantisation noise components while accepting an increased total noise power. The synthesizer is of particular advantage when used to generate the reference frequency for a frequency multiplier implemented as a phase lock loop. By making the dither sequence repetition frequency outside the phase lock loop bandwidth, the spurious components are removed from the frequency range of interest.

Abstract: Apparatus for detecting knots and the like in swan or planed timber comprising means for injecting light into the surface of the timber and means for detecting light emerging from the timber at a location spaced apart from the point or region of injection, a defect such as a knot in the timber, being indicated in dependence upon the amplitude or presence of the light emerging from the timber.