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CRF-23 0B
The
noise
is amplified,
rectified into negative
d-c voltage by diodes D210 and D211, and applied
to the base of transistor Q209 to turn it on.
Since
the base voltage of Q207 is controlled by the collec-
tor voltage of Q209, the amplification of transistor
Q207
increases
due
to increased
base
bias,
and
transistor
Q209
is held
conducting
quite reliably.
As
before,
transistor
Q608
cuts
off the detector
output.
Positive
feedback
through
resistor
R250
and
capacitor C239 from transistor Q209 aids in turning
off Q208.
CF501
($501-1)
R528
C526
330
33P
R528 C524
330
150P
Adjustable Selectivity Employing Ceramic
Filters:
The bandwidth in a-m reception can be altered
by changing
the coupling between
the sections of
ceramic filters in the a-m i-f circuit.
Ceramic filters
CF50!1
and CF502
can be manually
set to narrow
or wide bandwidth by switch S501.
The
net result of the switch manipulations on
the ceramic filter circuits are summarized
in Table.
The
overall
selectivity
curves
of the
a-m
i-f strip
are shown in Fig. 1-5.
Overall
CF502
($501-2 ~ 3)
response
(Fig. 1-5)
C527
R530
36P
2K
fe
mn [__]
C526
R529
100P
1K
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