Eliminating a birdie in the PRO-34 portable scanner

 PRO34.3


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.

CONTINUED IN FILE PRO34.9



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