GB569858A - Improvements in means for generating high-frequency electric oscillations - Google Patents

Abstract

569,858. Generating high - frequency oscillations. UNITED AIRCRAFT CORPORATION. July 13, 1943, No. 11404. Convention date, June 29, 1942. [Class 40 (v)] A voltage train generating means comprises a condenser, means for charging said condenser, an oscillatory circuit connected in parallel with said condenser, and a pair of output terminals for connecting said oscillatory circuit with a load circuit. The generator comprises a large condenser 11 which is charged to about one thousand volts through a resistance 12. Shunted across condenser 11 is an oscillatory circuit 13, 14 and the desired voltage trains are taken across 14 (or 13) and applied to the electrodes of crystal 3. The condenser 11 is also shunted by a grid-controlled gas-filled triode 15 normally biassed to cut-off by a source 16. On the application of a 60-cycle voltage through transformer 17, the triode 15 periodically conducts to discharge condenser 11 suddenly and generate 60 trains per sec. of voltage waves of a frequency (about 5 megacycles) determined by the combination 11, 13, 14. A lead 19 is connected to the synchronising terminal of a time base unit (not shown). Means for shortening the wave trains comprises a gas-filled triode 20 connected in series with a resistance 21 across the crystal 3. The triode is normally biassed to cut-off by a source 22. The grid of triode 20 is connected through a time-delay network 25, 26 to the anode of a one-stage amplifier 24 whose input is connected to one terminal of condenser 11. When condenser 11 discharges the consequent negative impulse drives amplifier 24 to cut-off and allows the upper terminal of condenser 26 to go less negative until after a time interval, at an instant when the anode of 20 is positive, valve 20 conducts and the oscillation is completely damped within a half cycle. This arrangement produces wave trains in which the individual waves throughout each train are in the same phase as corresponding waves of other trains, thus giving a stationary reflection pattern. In modifications, the means for shortening the wave trains are omitted (Figs. 3, 3a, not shown). Alternatively (Fig. 3a not shown) the condenser 11 may be discharged through a triode in series with a resistance, and the voltage across the resistance is used to start the oscillafory circuit into oscillation. The generator is described in its application to detecting flaws in solid objects by means of supersonic vibrations as described in Specifications 569,872, 569,8<7>3 and 569,874, [all in Group XXXVIII]. U.S.A. Specification 2,280,226 also is referred to.