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Realistic Pro- 34 Mods
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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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