Yaesu FT-902DM, Instruction Manual

Page: 25 / 55

FM UNIT ( P B-1 707B)
In the FM mode , the I F signal from the I F UNIT
is fed to the gate of Q9 o
i
( 3 S KS 1
),
where it is
heterodyned with the 9442 . 5 kHz signal delivered
from the FM oscillator Q902
(2SC 1 8 1 SY), thus
producing a 45 5 kHz IF signal. The 45 5 kHz IF
signal passes through a two-stage ceramic filter
consisting of CF 901 and CF 902
( LF B- 1 S ) , and is
amp li fied by an amp lifier limi ter consisting of Q9 0 3
(2SC 1 8 1 S Y) and Q904 (TA7 061 AP) .
A ceramic discriminator consisting o f CD901
(CFD4 S S S4 ) and D 902 and 0903 (both 1 S 1 8 8FM)
produces an audio output in response to a cor­
responding frequency shift in the 45 5 kHz I F
signal. T h e discriminator output i s amplified by
Q908
( 2SC 1 8 1 SY)
and fed to the AF UNIT at
pin 6 .
0901 3SK51
I
C901
0901
C902
t2V
3
' 2.2K
When n o carrier is present in the 45 5 kHz I F , the
n oise at the discrimin ator ou tput is amplified by
Q 905 and Q906 (both
2SC 1 8 1 SY) and detec ted
by 0905 and 0 906 (both
1 S 1 88FM )
to prod uce a
DC voltage . This voltage is applied to tu rn "on"
Q 907 ( 2 SC 1 8 1 SY). With Q907 "on, " the base of
Q 908 is grounded to q uie t the audio amplifier.
When a carrier is present, the quie ting action of
the receiver removes noise from the discriminator
output and Q907 is turned "off, " permi t ting
n ormal ac tion of Q908 . The squelch con trol Y R 901
sets the squelch threshold level.
+
-
C936
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