A device for tuning, and measuring the band width of, band pass filters or separate oscillatory circuits

摘要

662,280. Measuring coupling of coils. TESLA, NATIONAL CORPORATION, and CARNIOL, B. June 10, 1949 [June 24, 1948], No. 15579/49. Class 37. In order to adjust or measure the bandwidth of band-pass filters or to tune resonant circuits having any type of coupling a free oscillation is produced in one of the resonant circuits by means of a sudden change of current or voltage therein. A generator of square oscillations or a pulse generator G supplies to the coupled circuits F a square oscillation or short pulses of a given frequency. The output voltage of the secondary winding is either observed in an oscillograph O or rectified in a detector D, and is then applied to a measuring instrument M, the deflection of which depends only on the magnitude of the beat frequency produced by the difference in the frequency of the free oscillations in the two coils. One of the circuits is accurately tuned and all other circuits in succession are accurately tuned to the same frequency by varying their inductance or capacitance in such a way that the indicator M shows a minimum deflection all the time. This deflection represents a value which is proportional to the adjusted degree of coupling and hence also the resultant band width.