Abstract: An array of reed switches (13) is assembled on a circuit board (11) having a plurality of through-apertures (12) with one reed switch (13) disposed in each aperture with the axis of the switch envelope (14) extending perpendicularly to the plane of the board. A plurality of coils (16) is provided on the board so that each switch (13) is surrounded by a respective coil, the coils being connected to conductors on the board for operation of the switches. Also disposed is a control circuit wherein the reed switch drive coils (26) are connected in series across a constant-current voltage source and a respective solid-state switch TR1, TR2 . . . connected across each coil, with divers for each solid-state switch to permit operation of a selected reed switch.

Abstract: A variable resistor network has a coarse resistance network and a fine resistance network connected in series with the coarse network. The coarse resistance network comprises a chain of series-connected resistors any one or more of which may be switched out of the series by individual parallel-connected relays. The fine network comprises a shunt resistor together with a fixed resistor and a series-connected adjustable resistor together connected in parallel with the shunt resistor. A control circuit is arranged to control the relays for the switching of the resistors of the coarse network and also to control adjustment of the adjustable resistor. A chosen resistance value can be set by appropriate switching of the coarse network and adjustment of the adjustable resistor.

Abstract: An array of reed switches (13) is assembled on a circuit board (11) having a plurality of through-apertures (12) with one reed switch (13) disposed in each aperture with the axis of the switch envelope (14) extending perpendicularly to the plane of the board. A plurality of coils (16) is provided on the board so that each switch (13) is surrounded by a respective coil, the coils being connected to conductors on the board for operation of the switches. Also disposed is a control circuit wherein the reed switch drive coils (26) are connected in series across a constant-current voltage source and a respective solid-state switch TR1, TR2 . . . connected across each coil, with divers for each solid-state switch to permit operation of a selected reed switch.

Abstract: A variable resistor network has a coarse resistance network and a fine resistance network connected in series with the coarse network. The coarse resistance network comprises a chain of series-connected resistors any one or more of which may be switched out of the series by individual parallel-connected relays. The fine network comprises a shunt resistor together with a fixed resistor and a series-connected adjustable resistor together connected in parallel with the shunt resistor. A control circuit is arranged to control the relays for the switching of the resistors of the coarse network and also to control adjustment of the adjustable resistor. A chosen resistance value can be set by appropriate switching of the coarse network and adjustment of the adjustable resistor.

Abstract: A low noise sinusoidal signal at a desired output frequency is synchronised using a first variable frequency oscillator (1) and providing a feedback control loop around the first oscillator (1) to generate a feedback control signal in successive frequ comparison steps using second and third frequency reference signals (44, 42). Each of the second and third frequency reference signals are derived from a first frequency reference signal, the second frequency reference signal (44) being compared with the output frequency of the first oscillator (1) to generate a frequency difference signal (43), and said frequency difference signal ( being compared in frequency with the third frequency reference signal (42) to generate said feedback control signal for the first oscillator (1), the frequency of the third frequency reference signal (42) being equal to the difference of the frequency of the se frequency reference signal (44) and the desired output frequency.

Abstract: Signal measuring apparatus (100) comprises a detector head (110) connected to a meter (112) by a cable (114). The cable (114) allows the meter to supply power and a RF local oscillator signal to the head (110), and the head (110) to send an intermediate frequency signal to the meter (112). The head (110) contains a mixer (120) for downconverting a test input at connector (116). The meter (112) receives the downconverted signal and measures its various parameters.