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Text File  |  1992-12-21  |  2.1 KB  |  62 lines
  1. Newsgroups: rec.video.satellite
  2. Path: sparky!uunet!usc!zaphod.mps.ohio-state.edu!cs.utexas.edu!torn!nott!bnrgate!bmerh85!bnr.ca!wizz
  3. From: wizz@bnr.ca (Boris Volk)
  4. Subject: Re: C3/C4 Bleedover
  5. Message-ID: <1992Dec21.140248.12806@bmerh85.bnr.ca>
  6. Sender: news@bmerh85.bnr.ca (Usenet News)
  7. Reply-To: wizz@bnr.ca (Boris Volk)
  8. Organization: Bell-Northern Research Ltd.
  9. References:  <9212181115@ltrnativ.UUCP>
  10. Date: Mon, 21 Dec 92 14:02:48 GMT
  11. Lines: 49
  12.  
  13.  Alan,
  14.        Your problem is probably that your feed is not in the exact center of
  15. the dish. When the feed is offset from the prime focal point, the side effects
  16. are reduced gain and decreased sidelobe rejection. I have noticed this on my
  17. father's system which is identical to my own, with the exception that I 
  18. installed guy-wires on my system. His system does have a slight bleed-over
  19. problem where mine does not. 
  20.  
  21.  Here's the gain patern for a properly adjusted dish 
  22.  
  23.                                  *
  24.                                 * *
  25.                                 * *
  26.                                *   *
  27.                                *   *
  28.                                *   *
  29.                               *     *
  30.                               *     *
  31.                               *     *
  32.                          *    *     *    *
  33.                         * *   *     *   * *
  34.                        *   ***       ***   ***
  35.  
  36.                             -2   0   +2
  37.  
  38.  
  39. and for a mal-adjusted dish:
  40.  
  41.                                  *
  42.                                 * *
  43.                                 * *
  44.                                *   *
  45.                                *   *
  46.                               *     *
  47.                               *     *
  48.                              *       *
  49.                              *       *
  50.                          * * *       * * *
  51.                         *   *         *   *
  52.                        *                   *
  53.  
  54.                             -2   0   +2
  55.  
  56.  Note that the gain at +/- 2 degrees is much higher in the second patern.
  57. It is this increased "beamwidth" that is causing your troubles.
  58.  
  59. Boris Volk
  60. Nepean Ont.
  61.  
  62.