Sony CRF-230B - Page 8

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