GB818180A - Improvements in or relating to transmitters for a.c. telegraphy - Google Patents

Abstract

818,180. Frequency and phase shift radio signalling; keying carrier frequencies. SIEMENS & HALSKE A.G. April 4, 1956 [April 4, 1955], No. 10332/56. Class 40 (5). [Also in Group XL (b)] Carrier telegraph signals are produced by modulating in amplitude, frequency or phase an oscillator whose operating voltage is derived wholly or in part by rectifying the applied telegraph signals. As shown, a common base transistor oscillator has applied to its collector and base positive operating and bias voltages respectively derived from rectifiers R1--R4 to which keying signals from terminals K1, K2 are applied, the base positive bias being obtained from the collector positive voltage developed across capacitor C2 by voltage divider resistors W2, W3, and the emitter being connected through D.C. stabilizing components W7, C9, W5 and C2 to a tapping or tuned circuit L2, C3. The inductor L2 is transformer coupled alternatively to a further inductor L3 or to a capacitor C6 by rectifiers R7-R12 selectively opened and blocked by + and - D.C. telegraph signals applied at K1, K2 so that the operative frequency of tuned circuit L2, C3 is varied accordingly. Frequency shift signals variable in amplitude by a potentiometer W8 serving also for impedance matching to an output filter are thus produced. Two diodes R5, R6 in parallel opposition may be connected in series with resistors W4, W4<SP>1</SP> across the tuned circuit L2, C3 to stabilize the oscillator output against variations in operating voltage, the resistor W4<SP>1</SP> having a negative temperature coefficient to compensate for temperature changes in the diodes R5, R6. In a modification, on-off A.C. signals are produced by applying + and - D.C. keying voltages to a balanced rectifier bridge at the output of the oscillator. Phase shift keying is also referred to.