copied from UUCP:
Newsgroups: rec.radio.shortwave
Subject: Eliminate the birdie in your PRO-34 scanner
Keywords: scanner radio, birdie, dead carrier
Organization: AT&T Bell Laboratories
x
                   PRO-34 BIRDIE ELIMINATED
                     by Bob Parnass, AJ9S

   Birdies are unwanted signals generated within a receiver,
   which  cause the receiver to "hear itself."  Some birdies
   are caused by the unwanted product of the local  oscilla-
   tor.   Another  cause  is  a  stage, which oscillates but
   isn't meant to oscillate, such as a high gain  intermedi-
   ate frequency (IF) amplifier.

   Most birdies,  especially  those  generated  by  a  local
   oscillator,  are frequency stable.  It's difficult to rid
   a radio of these birdies, and solutions  usually  involve
   better internal shielding and isolation among the stages.

   A "wandering birdie"  is  one  which  changes  frequency.
   Wandering birdies, and birdies which appear and disappear
   suddenly, may be caused by  intermittent  ground  connec-
   tions within the radio, or defective bypass capacitors.

   After using his Radio ShackO PRO-34 portable scanner  for
   a  few months, Ron Smithberg, a fellow radio hobbyist and
   RCMA member from Joliet, was  hampered  by  a  "wandering
   birdie."   Ron's scanner was hearing itself on a few fre-
   quencies in the VHF-Hi range, but the birdie  disappeared
   when he tilted the radio or squeezed the case.  There had
   been no problem when the scanner was purchased initially.

   I suggested that a ground connection or a  circuit  board
   in  his  PRO-34  might be loose.  The thin PRO-34 plastic
   case feels chintzy, and can flex easily by applying  just
   a  gentle  squeeze.  After prolonged use, the case motion
   can loosen screws which were once tight.

   Ron disassembled his PRO-34.  He unfastened  the  helical
   antenna,  knobs,  and  rear screws, then gingerly removed
   the plastic case.  After Ron tightened a PhillipsO  screw
   holding  the  Logic  Board  to the front of the case, the
   birdie disappeared!

   The operation took a steady  hand.   Although  he  didn't
   have  to remove any boards, Ron warned that accessing the
   offending screw was a challenge.  He used  a  very  small
   Phillips  screwdriver,  positioned  through  a  hole in a
   shield partition.
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Bob Parnass, AJ9S - AT&T Bell Laboratories - att!ihuxz!parnass (708)979-5414