Patent GB-764597-A (GB)
IPC: G01R21/00
Abstract: 764,597. High-frequency voltage and power measurements. BIRD ELECTRONIC CORPORATION. March 25, 1954 [March 25, 1953], No. 8804/54. Class 37. A plug and socket device for indicating or measuring the propagated energy, the reflection coefficient, or the standing-wave ratio of highfrequency waves in a coaxial transmission line comprises a coaxial measuring section inserted in the line, having perpendicularly to the outer conductor thereof a metal socket open at one end to the interior of the line which at the other end receives an interchangeable metal plug which is a sliding fit for rotation about the principal axis of the socket, and which carries at its lower end an insulated pick-up loop inductively and capacitatively coupled to the inner conductor of the line and connected to a detector circuit comprising tuning capacitance and damping resistance for the loop, a crystal rectifier, and its associated capacitance-resistance load circuit, all insulatedly housed within the plug which is rotatable within the socket into either of two positions located 180 degrees apart by spring catches, in each of which the pick-up loop is disposed parallelly of the inner conductor to pick up energy travelling in either direction along the line; the rectified output of the loop being in each case connected over automatically closed contacts to a terminal and to an external measuring instrument, and a range of interchangeable plugs being provided to measure different energy ranges and frequencies. In a coaxial line there is inserted a short test section (Fig. 1) of similar characteristic impedance comprising a cylindrical outer conductor 1 and inner conductor 10 insulated by supporting annuli 11 and connectible to the line by bushes 4, 5 threaded into the outer, and having threaded reduced diameter portions with internal insulating tubes 18 supporting inner terminal rods 12 with plugs and split sockets at opposite ends to engage the inner conductors of the line, whose outers are connected by internally threaded collars 6 engaging the threaded portions and surrounding a split sleeve 17 and a coned socket 16 carried by bushes 4, 5 to receive corresponding fittings on the cable. A brass ring 20 (Fig. 3) brazed to the outer conductor defines a cylindrical socket 21 normal to the line, having a circular opening 22 coincident with an opening 23 in the outer conductor which receives a removable pick-up unit rotatable about the principal axis of the socket. The unit (Figs. 3, 8, 9) comprises a brass base 25 and cap 26 spigoted together and interconnected by studs 27, which define an enclosure accommodating a brass contact disc 35 and a brass plate 36 insulated from each other by dielectric discs 37, 38; the latter being all of the same diameter as the base to slide within the skirt of the cap and are surmounted by a dielectric block 39 fitting a reduced diameter chamber in cap 26, while disc 35 has a smaller diameter than elements 36, 37, 38 to ensure insulation. The stacked elements 35 to 39 have aligned apertures for the securing studs, which electrically connect the base 25 contacting the socket 21 to the plate 36, but are insulated from contact disc 35 by sleeves 50 (Fig. 9). Annular button capacitors 51, 52 (Fig. 8) of capacitances C1, C2, comprising ceramic discs 54 faced with metal plates 55, 56, are mounted in recesses 59 of opposite faces of the closure of base 25, with their plates 56 soldered thereto, while the outer plates 55 of less diameter than the ceramic discs are respectively soldered to sheath 65 of a germanium or other semi-conducting crystal rectifier 61 and to a disc 71 whose stem 72 extends through the centre apertures of the capacitors and the base closure and carries rod 64 connecting it to one pole of the crystal, whose opposite pole is connected to sheath 65, which alignedly supports it by annular glass insulators 67, 68. Contact disc 35 is provided (Figs. 5, 6) with two diametrically opposed radial lugs 76 protruding through axial slots 78 in the skirt of cap 26 to contact a finger 77 insulatedly mounted on ring 20 while clearing the inside of socket 21, and the sheath of the rectifier extends insulatedly through an aperture in elements 55 to 59 while its upper terminal rod 63 contacts a resilient finger 80 screwed to insulating block 39 which is connected through the rectifier sheath to plate 55 of capacitor 51 (having capacitance C2) and to an insulated carbon resistor 82 disposed in the hollow underside of cap 26, with its free end soldered to a conductor 88 which passes through insulating block 39, eyelet 89 (Fig. 4) forming one plate of a circular button-type capacitor 90 (of capacitance C3) mounted in a recess of plate 36 to which the remaining plate is soldered, and through insulating disc 37, being finally soldered to contact plate 35. The inner end of the pickup unit carries a rectangular pick-up loop 105 (Fig. 8) which is connected between disc 71 and the lower end of carbon resistor 98 (of resistance R) whose upper end 97 is soldered to the closure of base 25 and is partly accommodated in a socket 101 thereof; the resistor being sheathed with insulation 1 and surrounded by a capacitative shunting metal sleeve 100 (of capacitance C4) which is slidable over the resistor for adjustment and thereafter soldered into the socket, while the loop may include a flat loading coil 108 adjacent to disc 71 and a capacitance loading plate 150. The pick-up unit is rotatable by cap 26 into two positions 180 degrees apart at which the pick-up loop is parallel to the inner conductor, limited by a pin 110 (Figs. 1, 4, 5) projecting from the cap and movable through a cut-away segment of ring 20 to engage slidably adjustable screwclamped stops 109 located in recesses 111 of the ring (Fig. 4), while it is rotatably retained in position by a swinging spring-loaded latch 120 pivoted to the top of ring 20 to retain shoulder 131 of the cap 26. A D.C. galvanometer is connected over a coaxial cable 142 and connector 145 between contact finger 77 and the body of ring 20 to measure the rectified current derived from the pick-up coil, and Fig. 13 shows the equivalent electrical circuit of the device, wherein capacitor C1 tunes the pick-up loop to resonance over a broad frequency band damped by resistance R, whose shunting capacitance C4 is adjustable to regulate the directivity and frequency range of the pick-up loop. The loading capacitance and inductance applied to the loop are adjustable to regulate the resonant frequency and the power sensitivity while the latter is also dependent on the rating of the rectifier employed. Capacitances C2, C3 bypass RF from the rectified D.C. measured by the galvanometer, while providing together with load resistance 82 the required time constant for peak response of the galvanometer circuit. Interchangeable pick-up units of different power sensitivities and frequency ranges are provided, Fig. 8 and Figs. 10, 12 (not shown), whose power/frequency responses are set forth in Fig. 14 (not shown). It is shown, for a loop series resistance R, with mutual inductance and capacitance M and C between the loop and the inner conductor of a coaxial line of characteristic impedance Z 0 , and with reflection coefficient # = Er/Ef = - Ir/If where Er, Ef, Ir, If are the forward and reflected voltages and currents of a wave traversing the line, RC = M/Z 0  = K and e, edenote the loop pick-up voltages when M is positive and negative, i.e. when the pick-up unit is in two positions 180 degrees apart at which the inductive and capacitative e.m.f.s induced in the loop are respectively additive and subtractive; that e = 2j# E f K, e- = 2 j# E f  Kp, so that p = e-/e, and the power P transmitted along the line is given by: