FIRE-CONTROL RADARS FOR NAVAL VESSELS 



13 



energy would be dissipated in the receiver. Also, the minute received 

 energy would be partially lost in the transmitter outjjut circuit thus re- 

 ducing the maximum range. Because of the extremely short time in- 

 tervals between transmitted and received pulses, ordinary switching methods 

 cannot be used. A duplexing technique mentioned earlier was therefore 

 developed to provide this function. In the CXAS Radar this switching 

 was obtained by connecting the transmitter and receiver to the antenna 

 transmission line through adjustable lengths of coaxial line which were 

 preset for a given operating frequency to be effectively an odd multiple of 



Fig. 10 — CXAS — Modulation or pulse generator 



one-quarter wavelength long. During the transmitted pulse, a small 

 amount of the transmitted power overloaded the first tube in the receiver 

 and provided a low impedance at that point. Due to the line length 

 between receiver and junction point this low impedance is reflected as a 

 high impedance at the junction point with the result that very little power 

 is lost in the receiver line. At the end of the transmitted pulse the output 

 impedance of the transmitter consists only of the small inductance of the 

 output coupling loop and this impedance is reflected by proper choice of 

 Hne length as a very high impedance at the junction joint with the receiver 

 Ime. Thus, most of the received echo is directed to the receiver input 



