GB771246A - Improvements in or relating to pulsed eleetron discharge systems - Google Patents

Abstract

771,246. Radar; sawtooth generating circuits. RAYTHEON MANUFACTURING CO. April 29. 1954 [Sept. 30, 1953], No. 12464/54. Classes 40(5), 40(6) and 40(7) The I.F. amplifier of a pulse radar receiver consists of two parts, the first has a low Q and is continuously operative; whilst the second has a high Q and is normally inoperative, but is rendered operative for a period depending upon the range setting of the receiver by a pulse derived from the transmitter modulator. The low Q stage 25 is fed via a preamplifier from a mixer/duplexer, Fig. 1 (not shown) associated with a common transmit/receiver aerial. The resistor 31 damps the input circuit so as to prevent ringing when excited by the transmitted pulse. This stage is coupled to the high Q stages 41, 45, 46 which are normally cut-off by negative grid bias from line 144. The bias is tapped via rectifier 152 off a potential divider 148, 149, 150, 151, connected between -300 volts and earth. A pulse generator 10, 11 controlling the transmitting magnetron also controls a single shot multivibrator 20 which produces positive pulses of a duration determined by the range switch 107 which controls the circuit time-constants. These pulses are passed by cathode follower 22 to the gating bias line 144 which rises in voltage until rectifier 153 conducts and condensers 156, 158 (previously charged negatively via resistors 155, 157 in accordance with the voltage across resistor 151) discharge through resistors 157, 154 and 142 thereby determining the rate at which the voltage of line 144 continues to rise. The line 144 is ultimately held at earth potential for the remainder of its duration by rectifier 146. The sloping portion of the leading edge of the gating pulse thus obtained reduces the reception of background noise immediately following the outgoing signal pulse which would mask close-in targets. The output of the I.F. amplifier is passed by a detector and video amplifier 18 to the C.R.T. 19. Sawtooth generator. The time base for the C.R.T. 19 consists of a beam tetrode 160, the screen of which is pulsed by the multi-vibrator 20 via cathode follower 22, to apply a rectangular current pulse to the scanning coil 162 forming part of the anode load. When the range selector switch 168, 177, is, as shown, in the "one mile" (minimum range) position, anode load resistors 165, 166 are shorted out, and the voltage drop across resistor 164 is applied via resistor 179 and a cathode follower 172 to the control grid of the tetrode 160 so as to maintain a constant current. The resistor 179 is shunted by a capacitor 178 which gives the scanning current pulse a sloping top to compensate for I.R. drop in the coil 162 and so linearize the scan. The cathode follower 172 is rendered conductive only during the scan by connecting the anode to the control pulse source 22. When a range other than "one mile" is selected, the feed-back circuit is disconnected and the grid of the cathode follower 172 is connected to H.T.+ through a variable resistor 181, and through selected capacitors 182a to the junction of resistors 164, 165 in the anode circuit of the tetrode 160. The sweep timing is then determined by the time constant of resistor 181 and capacitor 182a, the maximum deflection current being limited by feed-back to the cathode follower of the voltage drop across resistor 164.