GB678383A - Means for frequency stabilization - Google Patents

Abstract

678,383. Frequency measurements. RADIO CORPORATION OF AMERICA. Sept. 26, 1949 [Nov: 4, 1948], No. 24679/49. Class 37. [Also in Groups XXXV and XL (b)] The frequency of an oscillator is stabilized by the use of a molecular-resonant gas cell, the transmission-frequency characteristic of which, T2, Fig. 1c, has a maximum at a standard operating frequency fg and a minimum at slightly higher and slightly lower frequencies f1, f2. This characteristic may be produced by subjecting the cell to a magnetic field, or by the use of a gas or mixture of gases having closelyspaced absorption lines. As shown in Fig. 2, the oscillator 10 feeds through a guide 11 to the cell 12, which is subjected to a magnetic field by coils 14 energized by a D.C. source 15 in series with an A.C. source 16. The wave amplitude at the cell output, which varies in the rhythm of the A.C. is detected by a rectifier 19, amplified at 20, and applied as one input to a phasecomparer 18. The other input is supplied from the A.C. source 16 through a phase-adjuster 17. Output from the phase-comparer 18 varies in sign and magnitude with the frequency deviations of the oscillator 10 and is used either to indicate the error, or to correct it as by connecting the output in the reflector electrode of the klystron 10. In a modified circuit, Fig. 4, the cell 32 which has a transmission characteristic as shown at T2, Fig. 1c, is traversed by waves from an auxiliary oscillator 29 whose frequency is swept over a range including the frequency at which the cell gives maximum transmission. A pulse output from the cell is compared in phase at 18 with the pulse output obtained by mixing at 28 the frequency-swept waves 29 with waves from the main oscillator 10, and passing the beat frequencies through a filter 30 and tuned amplifier 31. The phasecomparer output is a measure of the frequency deviation of the main oscillator 10. In Fig. 6 (not shown), the cell 32, Fig. 4, instead of providing closely-adjacent absorption lines by virtue of the use of a chosen gas or mixture of gases, makes use of a gas with a single absorption line which is split by applying a unidirectional magnetic field to the gas Reference has been directed by the Comptroller to Specification 663,065.