Yaesu FT-901DM Instruction Manual page 24

The output from the IF second mixer is fed
through a m on ol i thic fil ter XF 402 to the two-s tage
IF ampl i fier c on sisting of Q403 an d Q404 (b oth
3 SK40M ) . Th e ou tpu t from Q403 is coupled to
the rej ection tuning circui t which eliminates in ter­
fe rence within the I F passban d . This rej ection
function is accompl ished by varying the resonan t
frequency o f a crystal wi th varactor diode 0 40 6
( 1 S2209)
on the S S B , CW ,
The amplified I F signal is fed to t h e CARRIER
AM
UNIT. In the mode , the signal is fed through
a bu ffer amplifier Q4 1 0
detector D407 ( 1 N60) .
the AF UNI T .
A p ortion o f t h e ou tput from Q4 1 0 is rec tified
by D41 1 an d D 41 2 ( 1 N60)
The AGC vol tage is amplified by DC amplifier
Q 4 09 (2SC3 7 3 ) and fe d to the gate o f RF am p l fier
Q 1 01 and to IF amplifiers Q403 and Q404 to c on trol
the gain of these stages for AGC purpose s. Th e
tim e constant of the AGC vol tage d ecay is select­
(FAST /S LOW)
able by swi tch S 2003 . The AGC
vol tage is further amplified by Q408
and Q407 ( 2 S A 5 64A)
tion on th e front panel S-me ter.
I
and FSK m od e s .
(2SC 1 8 1 5 Y ) to the AM
The sign al i s then fed to
to produce AGC vol tage .
(2SK l 9GR)
for sign al strength ind ica­
0402 R413 R414 0403
151007 180 1 80 !SI007
2SC735Y
0406
2SCl815Y
The RF GAIN c on trol on the front panel varies
the AGC v ol tage level, providing manual control
of the gain of the RF and IF stages.
Q41 1 ( 2SC3 7 3 )
rejection tuning circui t.
(2SC7 3 5Y ) supplies the vol tage to the drain o f
Q401 and Q 402 when the transceiver re turns to the
receive mode a fter transmission.
0404 3SK51-03
0403 3SK 5l-03
-··---------�----·--
0407
2SA564A
- 22 -
works as a relay driver for the I F
Delay transistor Q4 1 2
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