GB556641A - Improvements in or relating to means for generating oscillatory electric currents of precise frequencies - Google Patents

Abstract

556,641. Indicating apparatus. FINDEN, H. J., and PLESSEY CO., Ltd. March 11, 1942, No. 3235. [Class 37] [Also in Groups XL and XXXVIII] A generator for producing a precise irequency comprises a controlled multi-vibrator 23 feedinga harmonic selecting amplifier26 or which the output is applied to a balanced modulator C which is also led with trequency derived from an inverter or phase-splitting valve 90 fed with a frequency representauve or the following digits derived from a similar balanced modulator B. To provide adequate separation oetween the modulating irequencies and the output if the modulator C is led with harmonics of 1 Mc. and the modulator B with harmonies of .1 Mc. frequencies up to .5 Mc. are obtained by using the dinerence between their complements and the next highest harmonic from the 1 Mc. unit instead of by simple addition as in the case ot frequencies. above .5 Mc. In this way adequate filtering in the amplifiers F1, F2, F3 preceding the inverter valves 78, 90, 97 is obtained. A voltmeter 103 may be associated with the output to facilitate the tuning of the filters which is effected on each range successively by operating the switch 7U which connects the outputs to the inverter valves 69, 78, 90, 97 alternatively to the output. When a digit is O the preceding modulator is unbalanced by operation of the appropriate switch 100, 101, 102. The stages may produce frequencies related by some other scale than the scale of 10. Indicating scale.-Fig. 2 shows the indicating dials for switches 29, 41, 54, 64 for selecting the harmonics operated by knobs 110 - 113 which are provided with 8 scales and masks 116 each formed with 8 windows 117 arranged in a spiral the masks being geared together and to a knob 119 having an indicator to show the scale used. By this means the switches may be set to indicate (1) the frequency indicated by the scale, (2) the next higher frequency, (3) the complementary frequency to that indicated, (4) the complementary frequency to the next higher frequency. In this way the required frequency is derived from the sum or difference frequency necessary to facilitate filtering and a cam 134 is driven to illuminate the appropriate scale associated with the filter tuning knobs 122, 126, 135. The correct mask position and the appropriate switch operation for unbalancing a modulator may be ascertined from a table, Fig. 3 (not shown), or by an indicator, Fig. 5, in which setting of switches 151, 160, 164, 172 cause operation of one of the indicating lamps 1 - 8 and one of the lamps A, B, C indicating the unbalanced modulator and effecting the unbalance at contacts 1001, 101<SP>1</SP>, 1021 under the control of series relays so that a modulator is unbalanced when there is no output from the filter feeding that modulation. The Provisional Specification describes a system of setting the oscillator to the required frequency in accordance with the digit values with the aid of four colour scales.