GB487502A - Improvements in or relating to thermionic valve oscillation generators - Google Patents

Abstract

487,502. Valve generating circuits. FERNSEH AKT.-GES. Dec. 21, 1936, No. 35099. Convention date, Dec. 20, 1935. [Class 40 (v)] In an oscillation-generator of ultra-high frequency an inductance 9, which. may be shunted by a condenser, is inserted between the tuned circuit I and cathode in order to counteract the phase lag due to the transit time of the electrons, and thereby to stabilize the oscillations over a range of frequency. The inductance resonates with the earth capacity of the cathode at a frequency below the working frequency. If the transit time were negligible the anode potential and grid potential would differ by 180‹ in phase, but actually the phasedifference is substantially less than this owing to the transit time, and in consequence the frequency of the oscillations generated may differ from the natural frequency of the circuit I so much as to render the oscillations unstable. The vector BA, Fig. 4, representing the potential difference between the point B and anode A when the circuit I is oscillating at its natural frequency so as to behave as a pure resistance, is combined with a vector KB representing the potential difference between the point B and the cathode, to produce a vector KA which represents the actual potential difference between cathode K and anode A under optimum conditions, and similarly the vectors KB, BG combine to produce the optimum grid-cathode vector KG. The requisite vector KB is produced by inserting an inductance 9 in shunt with the earth-capacity 10 of the cathode, and the pair 9, 10 is so tuned that its impedance is capacitive at the oscillation frequency, and the angle between the vectors KA, KG decreases as the frequency increases. A similar arrangement is adopted when the grid circuit, Fig. 3 (not shown), or both grid and plate circuits, Fig. 4 (not shown), are tuned, or in capacitycoupled oscillators the natural capacity 10 of the cathode may be supplemented by a condenser which may be ganged with the tuning-condenser. The earth-capacity of the cathode may be reduced by inserting highfrequency chokes 8 in series with the heater 7 and by earthing the metallizing of the calve and the screening or suppressor grid directly instead of through the cathode. According to the Specification as open to inspection under Sect. 91 the inductance 9 may be replaced by a resistance, but this subjectmatter does not appear in the Specification as accepted.