Abstract: A combined frequency and modulation measuring instrument contains a frequency counter which provides a direct indication of a carrier frequency and which is used to control the frequency of a local oscillator by means of which a modulated carrier frequency is converted directly to a required intermediate frequency.

Abstract: In a swept frequency oscillator arrangement compensation is provided for the non-linearities in the tuning sensitivity of the oscillator. The non-linearities are initially measured and stored. Subsequently the stored values are used to control the rate at which the clock pulses are integrated to produce a control signal for the oscillator.

Abstract: A protection circuit suitable for use with electronic test equipment contains a switch which is open circuited if an overload condition is detected. The opening of the switch isolates the overload detector from the applied overload thereby allowing the detector to have a relatively low power handling capability. If the switch is manually closed whilst the overload condition persists the switch is automatically re-opened within a short predetermined time.

Abstract: A modulated signal source derives its modulation information from digital data held in a data store. The digital data is arranged to operate a switch which in the case of amplitude modulation produces pulses of carrier frequency and in the case of frequency modulation introduces phase transitions into a carrier frequency. The use of the digital data and the switch enables the modulation characteristics of the signal source to be exactly predictable and reproducible and it is not degraded by non-linearities of the kind introduced by conventional mixers.

Abstract: In a frequency modulation system, the frequency modulation sensitivity of an oscillator is itself a function of the carrier frequency of the oscillator. The frequency modulation sensitivity is measured and stored for particular carrier frequencies, and subsequently used to control the amplitude of the modulation signal, so that when a frequency modulation signal is fed to the oscillator, a frequency deviation is obtained which is accurately related to the amplitude of the modulation signal.

Abstract: A spectrum analyser uses a monochrome cathode ray tube to display frequency information. A color swtich incorporating a layer of liquid crystal material and colored polarized dichroic plates is positioned in front of the display screen of the cathode ray tube and by operating the color switch in an appropriate manner a colored display is produced.

Abstract: A microwave attenuator consists of a plurality of variable attenuation PIN diodes connected in a serial path. At least one of the diodes forms part of a feed-back loop so that the attenuation level it provides can be adjusted to correspond with a reference signal. The effective level of the reference signal is modified in accordance with correction factors, by means of which non-linearities in the performance of the remaining diodes can be compensated.

Abstract: An R.F. signal generator is arranged to provide an output signal having a controlled level, by means of a feedback loop into which an additional frequency dependent control signal is injected. This additional control signal is derived from a resistor network in which particular resistors, or combinations thereof, are selected in dependence on the output frequency of the signal generator.

Abstract: A control device for electronic apparatus is provided with a d.c. ironless motor coupled to a manually rotatable knob. As the knob is rotated a digital signal representative of the rotation is derived from the back e.m.f. of the motor.

Abstract: The invention concerns micro-circuit arrangements in which two micro-circuits each consisting of an assembly of components and/or micro-strip conductors within individual compartments, are interconnected. In the arrangement provided by the invention the individual compartments have a common wall in which a gap is provided adjacent the ends of a micro-strip conductor in each micro-circuit and a bridge piece is provided to fit into the gap, which bridge piece consists of a block of dielectric material carrying a conductive member which connects with both micro-strip conductors adjacent the gap.

Abstract: A manually rotatable control knob is coupled to a d.c. ironless motor which maintains rotation of the knob once it is initially spun by hand. The initial back e.m.f. of the motor is sensed and is used via a feedback loop having a particular time constant to determine the subsequent rotational speed of the knob. By correctly profiling the time constant the inertial effect of a heavy flywheel can be simulated.

Abstract: An A.M. signal generator having an r.f. level control arrangement includes a modulator whose output gain is controllable, a detector for detecting the A.M. wave produced by the modulator and means for sampling and storing the output of the detector at times occurring when the modulating wave passes through a predetermined amplitude level. The sampled and stored signal is then compared with a D.C. voltage and the resultant of the comparison is applied back to the modulator in opposite fashion to variation in the level of the A.M. wave.