Patent GB-567639-A (GB)
Title: Improvements in or relating to electrical apparatus for the measurement of electrical impedances at high frequencies
IPC: G01R27/02
Filed: 1940-12-17
Abstract: 567,639. Artificial lines. HOLMAN, H. E., and CORK, E. C. Dec. 17, 1940, No. 749/42. Divided out of 567,637. [Class 40 (iii)] [Also in Group XXXVI] Apparatus for measuring impedances at high frequencies comprises cylindrical conductors 1, 2, 3, 4 branching from a common point 5 to form a cruciform structure. The conductors 1, 2, 3 are provided with axial conductors 6, 7, 8 electrically connected together at the point 5. Pistons 9, 10 slide on the conductors 6, 7 within the conductors 1, 2 so as to provide a low-impedance connection between the inner and outer coaxial conductors. The conductors 3, 8 are telescopic to permit adjustment of their length. The conductor 4 encloses a crystal detector 11 capacitatively connected to the point 5 by a plate 12 adjustable to and from the junction point 5 so as to vary its coupling. High-frequency oscillations are led in through a concentric feeder 13 attached to the piston 10 so that the outer conductor is connected to the piston and the inner conductor passes through the piston without making contact and is then looped round the conductor 7 so as to be slidable thereon and make contact at a point at which impedances will be matched. A high-frequency oscillator is connected to the feeder 13 and the piston 9 is adjusted until a meter indicating the rectifier current from the detector 11 shows a convenient reading. The piston 9 is then adjusted until for all lengths of the conductors 3, 8 the meter shows a zero reading. The piston 9 is then an exact number of half-wave-lengths from the point 5, and its setting is noted. A conducting cap is then applied to the ends of the conductors 3, 8 and the length of the conductors 3, 8 is varied until the meter reads zero for all positions of the piston 9. The length of these conductors is then an exact number of half wave-lengths of the applied oscillations. The piston 9 is then set to a position a quarter-wave-length away from its previously adjusted position, the cap is removed from the conductors 3, 8 and the piston 10 is adjusted until the meter gives a maximum reading, indicating that the source of oscillations is matched to the apparatus. The impedance to be measured is then connected between the outer ends of the conductors 3, 8 and the piston 9 is adjusted to give a maximum reading on the meter. The susceptance of the impedance is then determined from the position of the piston 9. To determine the conductance of the impedance, the piston 9 is adjusted until the voltage at the point 5 is reduced to 1/#2 of its original value at resonance. Two positions, one on each side of the resonance position, are obtained, and from these positions the conductance can be calculated. A sleeve attached to the piston 9 and projecting beyond the end of the conductor 1 may carry a pointer moving over a scale, for reading the position of the piston. The pistons may be of the kind described in Specification 567,637. The conductors 6, 7 may be formed by a stretched wire secured at points beyond the outer ends of the conductors 1, 2 to avoid insulating spacers. The conductors 1, 2, 3, 4 may be of circular' or other cross-section. The coaxial conductors 6, 7, 8 may be omitted and the system of coaxial lines converted to a similar system of wave-guides.