Abstract: A signal generator comprises a number of independent signal sources each of which can be controlled to generate predetermined frequencies and modulation. The outputs of these signal sources can be made available separately at output ports or can be combined within the signal generator to provide a combined output signal. The output signals are sensed at the output ports, and are calibrated against a stored correction tabulation to ensure that they have the correct signal level at the output ports. Such a signal generator is useful for the measurement and testing of complex electrical and electronic products.

Abstract: An equipment for testing electronic circuitry comprising: test connections to said circuitry; measurement means for generating test signals for application to said circuitry and monitoring response signals produced by the circuitry in response to the test signals, said test signals being applied and said response signals being received by way of said test connections; switches for switching the test signals generated to said test connections and the response signals produced to said measurement means; means defining the settings of said switches for a current test of a series of tests required to be performed on said circuitry; first memory means for storing the switch settings for the next test of said series following said current test; second memory means for storing the switch settings for the entire series of tests; and sequencer means for transferring (i) the next switch settings from said first memory means to said means defining and (ii) the switch settings for the test of said series following said n

Abstract: A frequency synthesizer for producing a tunable frequency output signal. The synthesizer includes a tunable frequency oscillator having a tunable output signal and including: a voltage controlled oscillator (VCO) for generating an output signal; a harmonic generator coupled to the VCO for generating a plurality of harmonics of the VCO output signal; and a tunable bandpass filter coupled to the harmonic generator and having an output for selectively passing any one of the VCO output signal harmonics which constitutes both the tunable output signal of the tunable frequency oscillator and the tunable frequency output signal of the frequency synthesizer.

Abstract: An apparatus for reducing display size whilst substantially maintaining display information content, the display comprising a graph plot of a number of data values, which plot extends in a first direction, each data value having an associated magnitude, the apparatus reducing the extent of the graph plot in the first direction. The apparatus comprises a digital signal processor (1), a data store (3), and a display system (5). The digital signal processor (1) comprises a program sequence unit (7), an arithmetic unit (9), and an address generator unit (11). The processor (1) divides up the data values into a series of groups of five adjacent data values each, selects from each group two data values having predetermined positions within that group for the purpose of preserving the presence in the graph plot of these two selected data values, and discards one of the three not selected data values from each group in dependence on the relative magnitudes of these three data values.

Abstract: An instrument which provides a measurement of the frequency and power of a microwave signal supplied to an input port of the instrument. The instrument includes: a resistive device which divides the microwave signal supplied into first and second microwave divisions thereof; a frequency counter which measures the frequency of the first microwave division, thereby providing the measurement of the frequency of the microwave signal supplied; and a power sensor and power meter combination which measures the power of the second microwave division. The power sensor and meter combination makes a calibration correction dependent on the frequency measured by the frequency counter to its power measurement, thereby providing the measurement of the power of the microwave signal supplied.

Abstract: A method of testing the electrical conductivity of a connection between an integrated circuit device (9) and a circuit board (7) to which the device (9) is connected. The device (9) includes a current path between a further connection (13) thereto and the connection (15) to be tested. The method comprises the steps of, while the circuit is inoperative: applying via the board (8) a potential of a first amount to the further connection (13); applying via the board (7) a potential of a second different amount to the connection (15) being tested; and positioning a probe adjacent the device (9) to sense indirectly current in the current path, the presence of current indicating that the connection (15) being tested is conductive.

Abstract: A waveform generator suitable for use in the testing of instrument landing systems comprising: a first generator (1) for generating digitally a first waveform comprising the superposition of a second waveform (19) of a first frequency and a third waveform (21) of a second frequency; a second generator (3) for generating digitally a fourth waveform comprising the superposition of a fifth waveform (25 or 27) comprising a phase reversed version of one (19 or 21) of said second (19) and third (21) waveforms of the frequency of said one waveform (19 or 21) and a sixth waveform (23 or 29) in phase with and of the frequency of the other one (19 or 21) of said second (19) and third (21) waveforms; and a circuit (7) for combining said first and fourth waveforms thereby to produce a waveform suitable for said use.

Abstract: Disclosed is a Device Under Test (DUT) fault detection and location circuit. A first circuit port is connected to the DUT for fault detection and location. A signal source for generating a series of signals across the operating frequency range of the DUT is connected to a second circuit port. A divider divides each signal generated by the source so as to provide first and second fractions of the signal, the second fraction passing to the device under test. A fault detection section provides a DUT fault detection voltage for each respective frequency. The circuit also has a branch including an impedance section and a fault location section. The branch receives the first fraction, and the fault location section provides a DUT fault location voltage for each respective frequency.

Abstract: A microwave synthesiser comprising: a plurality of oscillator sources (1, 13, 3, 15, 5, 17, 7), each for generating signals over a range of frequencies, said ranges of frequencies together extending over a total range of frequencies generated; phase locked loops (19, 31, 83, 37, 38, 41, 81) for phase-locking any selected one of said oscillator sources (1, 13, 3, 15, 5, 17, 7) so that it generates signals of a frequency at which it is set; a single low harmonic modulator (21) for modulating the signals generated by the selected one of said oscillator sources (1, 13, 3, 15, 5, 17, 7), the modulated signals passing to an output (27) of said synthesiser; and at said output (27) elements (25, 29) for detecting the power of the signals at said output (27), the modulation by said single low harmonic modulator (21) being controlled in dependence on the detected power thereby to control the power of the signals at said output (27).

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 variable frequency signal generator includes a phase locked loop having a variable frequency oscillator which has a control port to which a frequency determining signal is applied, the output of the oscillator being fed via a frequency divider to a phase sensitive detector where it is compared with a reference frequency signal, the result of said comparison being arranged to generate a comparison signal which is fed to a loop filter which is coupled to said control port; and the signal generator having a frequency control signal applied thereto and comprising a first path being arranged to adjust the division ratio of the frequency divider, and a second path including a combiner for combining said frequency control signal and said comparison signal to produce said frequency determining signal; and a calibrator for adjusting the relative characteristics of said first and second paths to compensate for effects arising from tuning sensitivity dependence on frequency of said variable frequency generator.

Abstract: An attenuator incorporates a matched circuit which directs a portion of the input power to a power detector (25). In response to the power level reaching a threshold value an actutor breaks the circuit through the attenuator to provide reverse power protection.

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: In many microwave applications poor repeatability of results is often caused by differences in the quality of the coaxial connections. This invention overcomes the problem by ensuring more uniform connection by providing two mechanical connecting means radially separated from each other and coaxial with a central conducting means being connected, thus ensuring precise alignment of the two conductors.

Abstract: A low-noise frequency synthesizer comprises a low-noise oscillator, such as a crystal oscillator, a multiplier, a divider and a phase-locked loop and is adapted to provide an output signal which is a combination of the multiplied and divided frequency. Thus, a large number of frequencies are available as an output in small increments determined by the division ratio of the divider.

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 detector for indicating the magnitude of a phase difference between two electrical signals applied to it, is provided with means for introducing a deliberate phase shift into one of the signals so that the measured phase difference never closely approaches 0.degree. or a multiple of 360.degree.. The detector is capable of providing a smooth output signal over a very wide range of phase difference which can exceed many multiples of 360.degree.. Furthermore, the phase comparator is never required to perform measurements in those regions of least accuracy close to zero phase difference.

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: A method of testing piezo-electric transducers includes locating one end (11) of a rod (10) of solid material over the active head (20) of the transducer, the rod (10) simulating the normal acoustic impedance presented to the transducer by the normal medium, in which the transducer is intended to operate, energizing the transducer and detecting the acoustic wave propagated through the rod at the other end of the rod. A loading rod for use in testing a piezo-electric transducer is an elongated solid body so dimensioned as to simulate the normal operating acoustic impedance presented to a piezo-electric transducer to be tested.

Abstract: A test arrangement for testing high frequency electrical devices consisting of two 6-port reflectometers which are both connected to a device under test. In order to calibrate the test arrangement, an arbitrary termination generator is connected to each test port while its test signal represents a reflectivity coefficient of greater than unity, so that it simulates active devices as well as passive ones.