SONAR AND RADAR 



World War II and have since been retired to pasture- 

 replaced by somewhat more efficient models. To make 

 the comparison more meaningful, I have selected a 

 typical airborne radar set which was a real triumph of 

 engineering skill in that it accompUshed, with a relatively 

 small weight and power consumption, as much as many 

 previous models that were far bulkier and less efficient. 

 This radar operated at a frequency of 9375 megacycles 



(X-3x X IQQ), or a wave length of 3.2 



y.j /J 



centimeters. While this frequency is vastly higher than 

 those used by bats, porpoises, or naval sonar systems, 

 the wave length is not greatly different because of the 

 much higher velocity of light or other electromagnetic 

 radiation. Where our sonar system emitted its acoustic 

 signals at a peak power level of 600 watts, this radar 

 developed a peak power of 10,000 watts. It is important 

 to stress that none of these systems, living or instrumen- 

 tal, emits power continuously; all have a relatively low 

 duty cycle, or ratio of time on to time off. In typical op- 

 eration this radar emitted pulses lasting 0.8 microsecond 

 (8 X 10~^ second) at a pulse repetition rate of 810 pulses 

 per second. In other words, every 1/8 10th second, or 

 1.23 X 10-3 second it emitted a pulse lasting 8 X 10""^ 

 second, followed by a silent interval about 1500 times 

 as long. This left ample time for echoes to return (at 

 the velocity of light) before the next pulse arrived. The 

 entire radar system weighed 124 pounds, but this does 

 not include the weight of the airplane generator which 

 supplied the electric power. This radar set detected air- 

 craft at 50 miles under most conditions and was a bril- 

 liant operational success. It is therefore of some interest 

 to inquire how well it compares with bat systems, watt 

 for watt of power emitted and gram for gram of weight. 

 This comparison is not a simple one because of the 



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