3. EQUIPMENT AND INSTRUMENTS 



57 



just their crystals so that the transmitted 

 signal from the first ship is stationary on 

 the indicator scope. See section 11:204 of 

 Special Publication 265A for information on 

 adjustment of the crystal oscillator. 



3-33 Shoran control system. — Shoran is 

 the name given to a special type of radar 

 system developed during World War II for 

 the purpose of accurately fixing the position 

 of an aircraft in flight. It was first used for 

 control of hydrography by the Coast and 

 Geodetic Survey in 1945. The position of a 

 sounding vessel is obtained by measuring the 

 elapsed time between a transmitted pulse and 

 the return signal from two fixed stations. 



A Shoran system consists of one ship 

 equipment, designated Radio Set AN/APN-3, 

 and two ground equipments designated Ra- 

 dio Set AN/CPN-2, each with all accessories 

 such as antenna system, transmission lines, 

 and power sources. Some ground stations 

 now in service are designated AVQ-5G(C) 

 and are converted AN/APN-3 equipments. 

 A more precise type of Shoran, called Hiran, 

 is available in limited quantities. Ship units 

 are designated AN/APN-84, and ground 

 units are designated AN/CPN-2A. 



The following manuals must be on hand 

 when Shoran equipment is being used : 



(a) Handbook of Maintenance Instruc- 

 tions for Radio Set AN/CPN-2. 



(b) Handbook of Maintenance Instruc- 

 tions for Radio Set AN/APN-8. 



(c) Instruction Manual — Model AVQ- 

 5G(C). Item (c) is a supplement to (b) and 

 is required only when converted ship equip- 

 ments are used. 



Special instructions and manuals will be 

 furnished with Hiran equipment. 



3-34 Shoran installations. — The Ship 

 Shoran unit consists of an indicator (Fig. 

 14), transmitter, and two small antennas. 

 Because of the noise created by a high-speed 

 blower in the transmitter case, the trans- 

 mitter should be located in a compartment 

 adjacent to the working area. The indica- 

 tor should be mounted near the plotting table. 



The ship antennas consist of two dipoles, 

 one for receiving and one for transmitting. 



These are mounted as high as possible on 

 the foremast. Ground planes for mounting 

 the antennas are supplied and consist of a 

 quarter-wave horizontal metal wheel mounted 

 on a framework of aluminum. The distance 

 between the antennas should not be less than 

 six feet because of mutual coupling. 



The MIMI (Mark 1, Model-1) Shoran an- 

 tenna is a recent development which has 

 proved satisfactory as a replacement for 

 dipole antennas. It is omnidirectional in a 

 horizontal plane and has elements mounted 

 on a single metal pole. This antenna is easier 

 to mount and has a 3 to 4 decibell gain as 

 compared with the dipole antenna and with 

 a smooth horizontal pattern. It may be used 

 at the mobile or ground station ; however, a 

 reflector cannot be used with the MIMI 

 antenna. 



3-35 Shoran ground stations. — The 

 choice of sites for the ground stations has 

 an important bearing on the performance 

 which can be expected of the system. The 

 antenna elevation above sea level should be 

 suflScient to provide line-of-sight coverage of 

 the area to be served. There should be a 

 minimum amount of land between the sta- 

 tion and the service area, and there should 

 be no obstructive upright metallic structure 

 within a half mile on line to the service area. 

 Sources of radio noise should be avoided, 

 such as high voltage power lines, radar in- 

 stallations, and automobile ignition systems. 

 The location should be reasonably level and 

 clear so that the mast can be erected and 

 guyed without diflRculty. 



When a reflector is used with the shore 

 station antenna, its position must be changed 

 from time to time as directed by the hydro- 

 graphic party. The reflector is rotated from 

 the base of the antenna by two lines at- 

 tached to the reflector for that purpose. Four 

 stakes set around the base of the tower at 

 the cardinal points of the compass will as- 

 sist the operator to orient the reflector cor- 

 rectly, especially when visibility is limited 

 by fog or rain. 



A shelter for the equipment is required. 

 The generator should be housed separately. 

 The AVQ-5G(C) requires only about 700 



