Abstract: A resonant circuit is provided with a number of phase shift circuits connected in series. A control circuit is connected in series with the phase shift circuits for controlling the direct current flowing through the circuits. One of the phase shift circuits is constructed of a pair of transistors interconnected by a capacitor. The emitter resistance of the transistors is determined by the direct currents flowing therethrough from the control circuit, whereupon the frequency of oscillation or resonance of the resonant circuit is dependant upon the emitter resistance.

Abstract: The invention relates to a writing system having a receiver in which a pen is moved over paper in response to signals received. The pen is driven by a pair of high torque, fast response servo motors having printed armatures, enabling the use of a ball point pen. The pen is connected to linkages carried by a pivotal cradle, the pivoting of which effects movement of the pen towards and away from the paper. The invention also embodies a transceiver and a transmitter of the writing system. The cradle is laterally fixed in offset relationship with respect to the writing area, and the motors are also mounted in fixed position to reduce inertia of the moving parts.