FIRE-CONTROL RADARS FOR NAVAL VESSELS 11 



hand wheel on the desk could be connected to the antenna turntable by a 

 shaft. The indicator employed a 7" cathode ray tube and dis[)Iayed the 

 radar signals by what is now known as a Class A sweep with a full scale of 

 100,000 yards. A pioneering feature of this indicator was the i)rovision of 

 a series of electronic range marks to increase the accuracy with which target 

 range could be read. Earlier indicators had used a ruled mask for the 

 range scale and had suffered in accuracy due to parallax, sweep non-lin- 

 earity, drift of sweep position, etc. The CX.'\S provided sharp pulses to 

 mark the 10,0()0-}-ard intervals along the sweep line, and smaller pulses to 

 mark the intervening 2,000-yard intervals. This system was free from 

 the errors of the ruled mask and permitted range readings accurate to 

 ±200 yards throughout the 100,000-}-ard scale. Provision was also made 

 to e.xpand any desired 20,000-3-ard segment of the scale to fill the entire 

 tube screen so that signals could be examined more closely. The ranges 

 corresponding to the 10,000-yard intervals were designated by illuminated 



RANGE-THOUSANDS OF YARDS RANGE-THOUSANDS OF YARDS 



Fig. 8 — CXAS — Range mark system 



numerals located directly below the electronic scale. The presentation 

 obtained with this arrangement is indicated in Fig. 8 which shows the 

 electronic calibration marks, transmitted pulse, and an echo at 43,000 

 yards on both the full and expanded scales. 



The third part of the CXAS equipment was an assembly known as the 

 Transmitter-Receiver or Main Unit. It was designed to be unattended in 

 normal operation and contained the Pulse Generator, Radio Receiver, 

 Power Control Panel, Radio Transmitter, and H.\'. Rectifier, which were 

 all built as removable drawer type units. .A side compartment in the 

 Main Unit also housed the duplexing circuits, gas equipment for the trans- 

 mission line, and some built-in test equipment, including a wavemeter and 

 monitoring rectifier. The Main Unit and its sub-units are shown in Figs. 

 9 to 14, respectively. A single -}'' coaxial transmission line provided con- 

 nection from the Main Unit to the antenna. 



In order to use a single antenna for both transmission and reception, 

 means had to be provided to effectively disconnect the receiver during the 



