GB600253A - Electric pulse modulation systems - Google Patents

Abstract

600,253. Valve modulating circuits; pulse modulation. STANDARD. TELEPHONES & CABLES, Ltd. Oct. 13, 1944, No. 19853. Convention date, Oct. 15, 1943. [Class 40 (v)] An arrangement for pulse-modulating a carrier wave comprises a device for absorbing energy from the resonant circuit determining the carrier frequency, the device being controlled by the pulses so that it alternately assumes absorbing and non-absorbing conditions, one of these conditions corresponding to the pulse durations. As shown, a sinusoidal voltage from a source 12, Fig. 1, is converted in a known cusper modulator 10, for example as described in Specification 600,244, and shaper 20 into rectangular pulses 26-... , 29 ... , which may be of positive or negative polarity. Voice or other signals applied, for example, through microphone 30, time modulate the pulses which are applied over line 22 to the grid of a triode 42, connected across the tuned circuit LC of the carrier frequency oscillator 33. The triode 42 is normally at zero bias, switch contacts 48, 49 being closed, and operates as a diode to absorb the energy of the carrier wave oscillatory circuit and prevent its operation. The modulated pulses bias the triode 42 to cut-off so that corresponding to each pulse the oscillator 33 operates to produce a carrier wave train 26a .... The pulse modulated carrier output is taken from an adjustable tap 62 on the load potentiometer 38 shunted by an A.C. voltmeter 60. To adjust the carrier amplitude, contact arm 48 is moved to contact 50, thereby biassing the tube 42 to cut-off. The potentiometer 37 is then adjusted to give a suitable reading on the voltmeter 60. A desired fraction of this value may then be obtained for the output by adjusting the tap 62 to the corresponding voltage-dividing ratio as indicated on the scale.