GB852253A - Improvements in or relating to automatic tuning devices - Google Patents

Abstract

852,253. Radio transmitting systems. PHILIPS ELECTRICAL INDUSTRIES Ltd. July 1, 1957 [July 4, 1956; Sept. 28, 1956], No. 20694/57. Class 40(5). A motor-controlled tuning stage is tuned to a required frequency corresponding to that of a pilot signal by applying the latter to a frequency discriminator comprising a variable reactance C1-C6 adjustable in steps and series resistance 3 continuously adjustable by the motor until the voltages across the reactance and resistance are equal, whereupon the motor stops. As shown, the voltages across capacitor C5 and resistance 3, 4 are respectively applied at terminal 6 and between terminals 6, 7 to rectifiers 8 whose differential output is applied to the coils 11, 12 of a polarized relay 9 whose contact 10 engaging terminal 13 or 14 drives tuning motor 16 accordingly. The motor 16 also drives through shaft 17 the variable resistor 3, e.g. a rotary potentiometer without a stop, to a maximum, minimum or other selected value, whereupon a cam 18 on shaft 17 engages closes contacts 22, 22<SP>1</SP> to energize holding windings 23, 24 on the relay and maintains the motor 16 energized while a driving arm 19, also on the shaft 17, engages a movement 21 and drives a shaft 20 and switch arm 2 stepwise to select a different value of capacitor corresponding to a new wave range to be traversed. The opposite end of the arm 19 also has an arcuate projection whereby the movement 21 is locked between switching steps. The cycle is then repeated till the voltages across the selected capacitor C1-C6 and resistance 3, 4 are equal, and the motor then stops and is locked by current through a winding 28 energizing a brake 29. The switches 22, 22<SP>1</SP> may be simultaneously operated as shown or may be pairs of switches angularly arranged at equal distances from the cam 18 and each pair connected in parallel, to increase the angle over which the cam 18 is effective. The differential output of the opposed rectifiers 8 may be applied to one grid of a double triode, the other grid of which is earthed, to derive an amplified reversible polarity output from the anodes applied to the relay coils 11, 12. The discriminator wave ranges may overlap provided the tuning ranges correspondingly overlap.