GB1246166A - An attenuator - Google Patents

Abstract

1,246,166. Attenuators. THORN RADIO VALVES & TUBES Ltd. 30 Jan., 1970 [16 Jan., 1969], No. 2695/69. Heading H1S. [Also in Divisions H3 and H4] An attenuator (for use as a probe) comprises a first resistor or resistor combination 10, 11, 12 (Fig. 4) connected in series with a second resistor or resistor combination 14, 16 across a pair of input terminals, two output terminals being connected to the ends of the second resistor or resistor combination 14, 16 which latter is a hollow generally tubular member surrounding at least the major part of the first resistor combination. In Fig. 4, 20 indicates the probe input and 21 the output terminal of the probe which in use may be connected to an oscilloscope through a coaxial cable 23. The outer resistor combination is formed of a synthetic resin bonded paper tube 15 having 11 bands 14 of copper foil connected together through 10 k # resistors 16. A trimming capacitor 24 may be provided to compensate for the effect of stray capacitance. Further compensation may be provided by shunting the two resistors 16 at the earthed end of tube 15 by a 6À8 k# resistor. The space between the resistors 10, 11, 12 and the tube 15 may be filled with silicone jelly. In another embodiment (Fig. 6) the first resistor 30 is formed of a hollow tubular member of uniform resistance along its length and is connected at its end remote from the input terminal 31 to a similar hollow tubular resistor 33 which surrounds it. Both may be surrounded by an earthed screen 34 and a central wire 35 is connected to the input terminal 31 and through a variable capacitor 36 to output terminal 32 to compensate for stray capacitance between 33 and screen 34. The wire 35 may be fed from the input through a 500: 1 capacity potentiometer.