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for  any  heading,  it  doesn’t  interfere  with  the instrument’s  practical  value. Most shipboard installations consist of one or more  master  gyros  located  in  close  proximity  to the steering station. The indications of the gyro are  transmitted  electrically  to  repeaters  located  on the bridge wings, at conning stations, and at other necessary points. Despite  the  excellence  of  the  gyro  mechanism, the magnetic compass (NOT the gyro) is standard equipment  aboard  ships.  Since  the  gyrocompass is  powered  by  electricity,  it  would  be  useless  if  the ship experienced a power loss. The gyrocompass is also an extremely complicated, expensive, and delicate instrument that is subject to mechanical failure. Some gyros, for instance, become erratic after a ship makes a series of sharp turns at high speeds.  For  this  reason,  the  magnetic  compass remains  the  reliable  standby.  It  constantly  checks the  performance  of  the  gyrocompass  and  stands ready at all times to take over if the gyrocompass fails. MAGNETIC   COMPASS The magnetic compass, which is the standard compass  on  Navy  ships,  operates  through  the magnetic  attraction  of  the  earth  itself. The magnetic compass is located in the pilot- house.  It  consists  of  a  magnetized  compass  needle attached to a circular compass card that is usually 7   1/2   inches   in   diameter.   Although   the   card appears  to  move,  it  actually  remains  stationary while  pointing  to  the  earth’s  magnetic  pole.  In reality,  the  ship  is  moving  under  the  compass card. For  the  magnetic  compass  to  give  reliable service,  it  must  be  properly  installed,  maintained, and protected from disturbing magnetic influences. COMMUNICATION  AND  RADAR ANTENNAS From an operational standpoint, communica- tion and radar antennas are a vital part of a ship’s equipment. The communication antennas provide us  with  command  and  control  capability.  Radar antennas are used to electronically search the sea and  sky  to  detect  objects  beyond  visual  range. They  are  also  used  as  navigational  aids  and  for fire  control  purposes. The  function  of  a  receiving  antenna  is  to intercept  a  portion  of  the  electromagnetic  wave emitted by a transmitting antenna. The function of a transmitting antenna is to convert the radio frequency  fed  to  it  by  a  high-voltage  generator into  an  electromagnetic  wave  that  may  be propagated  to  distant  points.  Radar  antennas  both transmit  and  receive;  some  communication antennas  also  have  that  capability. Whatever their purpose, antennas are located so that they receive the least possible amount of interference from each other and from the ship’s structure.  Most  of  the  masts,  stacks,  and  other structures abovedeck are grounded to the ship’s hull and, through the hull, to the water. For an antenna to obtain adequate coverage, it must be installed  so  that  the  electromagnetic  radiation pattern  from  grounded  structures  causes  mini- mum  distortion.  Radar  antennas  usually  rotate and  are  normally  mounted  on  platforms. Also   associated   with   the   radar   are   radar repeaters.  While  not  actually  a  radar,  they  receive input from a radar. They are located in different areas from the radar, such as on the bridge or in the  combat  information  center. Some   typical   shipboard   communication antennas include wire, whip, and high-frequency antennas. Wire and whip antennas are designed to operate through frequencies in the medium to high range. Ships need various types of antennas to  ensure  their  use  of  the  widest  possible  range of available frequencies consistent with available space. SUMMARY In this chapter you have learned about various external  equipment  found  aboard  naval  ships. Any  ship,  no  matter  what  its  mission,  must  be capable of mooring or anchoring. Hence, all ships must  have  ground  tackle. Hopes are that survival equipment will never be   needed;   however,   all   ships   must   have appropriate  survival  gear  available. 18-7

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