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BELL SYSTEM TECHNICAL JOURNAL 



that approximately 75% of the energy contained in the idealized original 

 pulse will be available after transmission through a band-pass structure of 



band width dimension of — cycles per second. A further doubling of the 



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2 

 band width to — cycles per second will increase the available energy by only 



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about 15%. In the case of the practical radar-pulse envelope which usually 

 is characterized by a trapezoidal form with finite rise and decay intervals, 



the energy contained at frequencies outside of a — band is reduced some- 



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what over the idealized case illustrated in Fig. 25. 





FREQUENCY 



Fig. 25. — Amplitude-time and energy-frequency relationships for a rectangular 

 radar pulse envelope. 



The signal-to-noise ratio of the radar receiver is dependent on the over-all 

 receiver band width as indicated in the previous section of this paper. It 

 is extremely important then to restrict the IF band width as much as pos- 

 sible, consistent with adequate transmission of the signal itself. The final 

 band width choice is that value where a further increase would result in a 

 noise increase greater than the corresponding signal improvement and where 

 a band width reduction would diminish the signal by a greater increment 

 than the nofke. The exact determination of the optimum radar receiver 

 banfl width must be carried out using the linal display device in making 

 the signal-to-noi.se comparisons. If the raflar system is to be employed for 

 search pur])oses where echo presence is the primary measure of the perform- 

 ance of the equipment, the optimum over-all receiver band width has been 



found to be of tfie order of cvcles per second resulting in an IF ampli- 



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 fier band width of — cycles per second to adequately tnmsniit tlie double- 



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