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TUCoPS :: Radio :: pro34_3.txt

Realistic Pro-34 Mods


Subject: Eliminating a birdie in the PRO-34 portable scanner
           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  oscillator.   Another  cause  is
   a  stage, which oscillates but isn't meant to oscillate, such as a
   high gain  intermediate 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  connections within the radio, or
   defective bypass capacitors.

   After using his Radio ShackO PRO-34 portable scanner  for a  few
   months, Ron Smithberg, a radio hobbyist in Joliet, was hampered by a
   "wandering birdie."  Ron's scanner  was hearing  itself on a few
   frequencies 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.

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