Abstract: A distortion compensating apparatus for use in IQ modulation and demodulation techniques wherein a first distortion arrangement distorts the I-signal by adding to the I-signal a first weighted function of the I-signal and a first weighted function of the Q-signal and a second distortion arrangement distorts for Q-signal by adding to the Q-signal a second weighted function of the I-signal and a second weighted function of the Q-signal, such that the weighted functions of the I-signal are independent of the Q-signal and the weighted functions of the Q-signal are independent of the I-signal. This enable distortions to be compensated in both sidebands of the IQ modulated signal.

Abstract: Monitoring a series of products of the kind in which the presence of foreign bodies in the product being monitored is detected by the characteristic magnetic field phase difference each material exhibits. The signal generated by a satisfactory product having no foreign body in it is used as the datum for judging whether the next subsequent product is free from a foreign body or not.

Abstract: Apparatus for synthesising a composite signal (53) which has spaced first and second frequency channels of which each has an independently predetermined power, the power of the first channel being substantially below that of the second, and each channel being frequency modulated by an independent signal, the apparatus including a generator (51) responsive to the independent signals and to representations of the said powers and to the channel spacing to generate a composite modulation signal, and a single, high purity radio frequency source (52) connected for modulation by the output of the composite modulation signal-generating generator to produce the composite signal (53).

Abstract: A frequency counter for counting pulses of a variable input signal (Fin) using another input signal (Fgate) of a different, fixed frequency as a reference, includes a noise-shaping synchronizer (20,23,24) for retiming pulses of the lower frequency input signal to have a fixed timing relationship with selected pulses of the higher frequency input signal such as to introduce substantially less phase noise onto the lower frequency input at low modulation rates that would be the case with a simple synchronizer; and a counter and a latch (11,12) responsive to the retimed pulses (13) and to the higher frequency input signal (Fin) to provide a data output representative of the ratio between the frequencies of the input signals.

Abstract: A frequency or phase modulator, in particular a DC-coupled frequency modulation synthesizer, comprises a voltage-controlled oscillator (1) in series with a divider (2) in a phase-locked loop, and an analog-to-digital converter (17) connected to control the divider in accordance with an input analog modulation signal. The converter (17), preferably a one-bit charge-balanced converter, has a noise-shaped frequency response to reduce noise at frequencies below the loop-bandwidth.

Abstract: A phase comparator accepts two streams of digital pulses, one being a reference signal and the other a test signal, and generates an output signal indicative of the phase difference. The phase comparator can be implemented as a four-state device or higher, and thus exhibits a wide phase capture range, i.e. multiples of 360.degree., and can provide a stable, predictable and linear output signal when the two input signals are in lock. It is therefore very suitable for use in a phase locked loop in which temporary wide variations in phase can occur.

Abstract: An attenuator is in the form of a pad comprising a coating of resistive material which connects an input port, an output port and a pair of linked constant potential ports. The regions of the pad adjacent to the outer edges of the input port are provided with outwardly pointing cusps with curved boundary edges. These reduce current crowding at the edges of the input port, and avoid localized overheating of the adjacent regions of the pad, which could result in pad failure.