GB654684A - Improvements in or relating to generating oscillations - Google Patents

Abstract

654,684. Pulsing carrier frequencies; generating oscillations. DEPARTMENT OF COMMERCE, DIRECTOR OF THE OFFICE OF TECHNICAL SERVICES OF. Feb. 27, 1948, No. 5934. Convention date, Jan. 11, 1944. [Class 40 (v)] Oscillations are generated by shock-exciting a resonant circuit, then suppressed by applying inverse feedback to the circuit, so that the oscillations begin and cease almost instantaneously and remain constant in amplitude intermediately. In Fig. 1 a positive gate pulse applied to the cathode of a valve 10 renders it non-conducting and shock excites through its resonant anode circuit a transformer-coupled balanced bridge circuit comprising a piezo-electric crystal 34, which circuit resonates with substantially pure sine waves from which shock has been eliminated due to its balancing, and with low decrement due to the series circuit of the valve 10 and its anode circuit being non-conducting. The oscillations are applied through amplifier valves and taken off from an output 56 and are further passed through a valve 59 to develop across a variable resistor 82 an opposing feedback to the valve 10 and crystal circuit, ineffective as long as valve 10 is blocked, but, on the gate pulse terminating and the valve 10 conducting, strongly damping or suppressing oscillation in the crystal circuit. In Fig. 2, a valve 90 at near cut-off due to the cathode resistor 92, is connected in series with a bridge circuit comprising three condensers 101, 102, 104 and a piezo-electric crystal 106, a diagonal tapped high resistance 108 balancing the bridge. A positive gate pulse applied to the cathode of a succeeding valve 137 (not shown) is fed back to the grid of valve 90 through a lead 150 to energize the valve and excite sinusoidal oscillations in the crystal bridge, which are maintained due to the valve 90 resistance being low and are passed to output amplifiers. On the positive gate pulse ceasing the valve 90 is driven to near cut-off so that its high resistance is between the condensers 101, 104 and the high resistance 108 is in series with the crystal, and the oscillations therefore damped. As before, the oscillations produce in part through the amplifier valves and valves 137, 90 an opposing feedback to the bridge suppressing oscillation.