January 1946 - ELECTRONICS - RADAR ON 50 CENTIMETERS - The TPS-3 Radar
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ELECTRONICS
January 1946

By Lt. Col. Harold A. Zahl
and
Major John W. Marchetti
Page 98 - 104
John Marchetti at Camp Evans
building 20 - January 1999
 evans logo
slowly for accurate azimuth orientation.
     The power unit and modulator are kept 50 ft from the tent and are connected to the console by means of cables.  The power unit is a single-cylinder gasoline engine driving a 400-cycle alternator and a dc generator mounted on the same shaft.  The radar components of the set use 400-cycle power, thus effecting a great saving in weight and size.  The dc generator produces 28 volts that is used to drive fan motors and the antenna turning motor.
     Unlike the SCR-268 previously described in ELECTRONICS, the AN/TPS-3 provides only range and azimuth information.  This information is displayed on the indicator on two cathode-ray tubes used in an A-scope and in a PPI-scope. T he A-scope resembles an ordinary test oscilloscope and presents a horizon-		 tal sweep line with the signal appearing as vertical deflections along this line. The PPI presentation employs a sweep line which starts at the center of the tube and sweeps outward toward the edge. This sweep line is made to rotate about the center of the tube in synchronism with the rotation of the an-tenna and therefore indicates the position of the antenna.  Signals are applied to this tube by intensity modulation so that they appear as bright dots on a dark background.  Both of these tubes indicate the range of the target by the distance of the signal from the beginning of the sweep line.  The PPI tube measures azimuth by noting the position of the sweep line when a signal appears.  The two forms of presentation are shown in Fig. 3.
     The pulse rate of the set is 200 pulses per second. The interval be-		 tween pulses is 5000 microseconds. Using a sub-multiple of the alternator frequency for timing the pulses provides a clear and steady picture on the indicators with a minimum of filter weight.  The transmitted radio-frequency power and the sensitivity of the receiver are such that the radar set will "see" a medium-size aircraft at 120 miles. The total time necessary to cover this 120 miles is approximately 1300 microseconds, and this amount of time is all that is used on each sweep of the cathode-ray tube.  The remainder is dead time.
     Figure 4 is a block diagram showing the flow of signals through the equipment. The modulator, in conjunction with a rotary spark wheel, mounted on the power unit, pro-duces high voltage dc pulses which are synchronous with the 400-cycle power supply at half its frequency.

ELECTRONICS  -January 1946                                                                                                              100

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