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COMMUNICATION-TELEVISION AND RADIO

  
RADIO   AND  TELEVISION   broadcaster     broadcast     electromagnetic   waves   from  a   high  transmission  tower.It  is  high  so  that   the  ultra short  waves can   have   the  largest  possible   range.These   waves   always    travel   in  a  straight  line,just  like  the  sun  rays.They  cannot  go  through   a  mountain.  so  there  is  no  reception   behind  a  mountain ,but  a  dead  zone.
The  curvature  of  the  Earth   to  is  an  obstacle  too,  and  the  waves    cannot   'encircle'  the  Earth.This  problem  is  solved   by  the  Satellites.Radio  waves  are  sent   in   a  straight   line  to  the  satellite  ,  which  then  sends   them   to  another  point  on  the  Earth,again  in  a  straight   line.
DIGITAL   TECHNOLOGY.
EARLIER  ,electrical  signals   were   transmitted  via  home   antennas,  or  cables.These  signals  got  converted  into picture  and  sound   in  television   sets.Now  this  technology  is replaced   by  digital  technology.In  this  technology  ,the  electrical  signals  of  images  and  sounds   are  converted  into   impulses  and  encrypted   or ' coded'  in  numbers.The  image  and  sound  data  are  decrypted    or  'decoded'   in  our  homes  ,so  that  we  can  see  the  original  program mes  .New  television  sets  can  decode  by  themselves,but  old  ones  needs  a  small   additional     device 'set top box'  .The   digital   signals   can  also  came   from  the  radio  stations  to  our   homes,this is  done  by  cable ,antenna,or  satellites.
LIVE  TELECAST.
MANY  BROADCASTER  SEND  the  latest  news  from  within  the city  or  from  far off  places.Their   television  teams  are  equipped  with  a  'broadcasting  Van'  so   that  we  can  see  the  pictures   and  report  'Live',i.e,  exactly   at  the  time  when  they  are  recorded.These  broadcasting  vans  are  equipped  like  a  studio and  can  send   everything  to  us  via  satellite. In  times  of  crisis   or  in  war  zones,reporters  often  have  just  a  telephone  at   their  disposal .In  such   live  transmissions,  the  connection  is   often  jerky  and   keeps  on breaking.
RECEIVING    FOREIGN  STATION.
FOREIGN  stations  can  be  received  by  Satellite  .For  this   ,a  satellite  dish,a  receiver, and  a   decoder  is  required.since  there  are  several    television  satellites   in   space , one  must  align   the  dish    with  the   satellite ,  whose  program mes   one  wishes   to  receive.

  

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