Patent GB-648696-A (GB)
Title: Improvements in and relating to pulse generating apparatus
IPC: H03K3/78
Filed: 1947-10-06
Abstract: 648,696. Frequency measurements. BRITISH THOMSON-HOUSTON CO., Ltd. Oct. 6,1947, No. 26804. Convention date, June 23, 1945. [Class 37] [Also in Groups XL (a), XL (b) and XL (c)] A generator of pulses of ultra-high-frequency waves, for use in frequency measurement and frequency spectrum analysis, comprises a cavity resonator, transmission line, or waveguide, shock-excited by pulses of current produced by the discharge of a condenser which is charged through a resistor from a unidirectional source and is discharged through a spark gap. The resonator, Fig. 1, comprises an axial tube 6 facing a stub 11 attached to the end plate 10 of an outer cylinder 7 which is shorted to the tube 6 by a plate 8 at the opposite end. The tube 6 is slidable through spring, contacts 9 and is adjustable axially by a piston 18 sliding within a tube 21 under the control of a screw 20. The nut 18 is threaded to engage the screw 20 and backlash is taken up by a second nut 32 pressed away from the nut 18 by spiral springs (Fig. 3, not shown). The screw is supported in bearings 24, 25 and is operated by a knob which is geared to a pointer 29 to indicate the resonance frequency of the resonator. A rod 27 acts as a guide for the nuts 18, 32. The spark gap 35, 36 is housed in a tube 44 projecting radially from the member 7 close to the plate 8. One electrode 35 is attached to a short rod 37 passing through an insulating sleeve 39 and forming within the resonator a coupling loop 38. The other electrode 36 is attached to a cylinder 45 which forms a condenser with the outer tube 44, being separated therefrom by an insulating sleeve 46. The cylinder 45 is connected by a screw 48, passing through an insulating block 47, to a carbon or like resistor 49 and the other end of the resistor is connected to a battery or other D.C. source 54 and to a byepass condenser 54<SP>1</SP>. The condenser charges through the resistor 49 until the gap breaks down, giving successive pulses of current through the loop 38 and setting the resonator into oscillation at its natural frequency. Output is taken by a loop 55 and a concentric line 57, 58 which may lead to a meter 4. To measure the frequency of a wave source, such as the receiving aerial 59, Fig. 4, the wave is mixed with the output 1 from the resonator of Fig. 1 to produce a low beat frequency which is mixed at 61 with a wave supplied by a source 62. The latter is varied in frequency until the lower side frequency passes a filter 64 to a second mixer 65. This mixer is also fed through filters from a fixed frequency source 66, giving a low-frequency output and producing an indication on the C.R. tube 70. The pulsed wave source of Fig. 1 is now adjusted until identity of input frequency is indicated in the tube 70, whereupon the frequency of the source 59 may be read on the pointer 29 of Fig. 1. A spark-gap pulse producer 3, Fig. 5, such as that shown in Fig. 1, may be used to send pulses into a length of coaxial line 72-73, and the output taken through a wave analyzer 74 to an indicating instrument. In this way the transmission characteristic and resonance frequencies of the line over a wide range of frequencies may be examined. A similar method may be employed to examine the transmission characteristic of a length of wave-guide, which may have discontinuities such as portions of enlarged crosssection (Fig. 6, not shown).