Yaesu FT-902DM, Instruction Manual

Page: 23 / 55

FI LTER UNIT
(PB- 1 99 5 )
The I F signal re ceived at p i n
2
o f the FI LTER
UNIT ( P B- 1 995 ) is amp l i fied b y p arallel-conn e c te d
0 30 1 and 0 305 ( b o th 2SK 1 9GR ) , and fed th rough
a m o n olithic fil ter XF 30 1 ( 8 . 9M-20A ) , which has
a ± 1 0 kHz band w i d th , providing addi tional se lec­
tivity and enough d e l ay time t o ma tch the noise
blanker gating pulses. Th e signal _is then fed to the
second I F amp lifie r, Q 3 0 2 ( 2S K 1 9GR ) .
T h e n oise b la n ker d i o d e 0 30 1 ( 1 S 1 007 ) is p l a ced
between T 302 and T 303 , and i t fun c tions as an
ON/OF F swi tch which is controlled by the noise
blanker d river 0 303 ( 2 SC 1 8 1 5GR ) . The outpu t
from the source o f Q 302 is passed through the
SSB
filter X F 304 ( or the optional AM or
CW
fil te rs ) .
Sele c tion of the fil te r to b e u s e d is performed b y
o n e of the diode swi tches 0 303 - 0 308 ( 1 S 1 007 ) ,
depend in g o n the m o d e o f operation. The I F
sign al i s then transfe rre d t o the I F UNI T . I n the
F M mod e , the IF signal is coupled d irectly through
0 31 0 ( 1 S I 5 5 5 ) to p i n
5
of the IF UNIT.
9
1 0
I I
1 2
18
I
I
I
I
0305
2SKl9GR
I PB- 1995
0303
2SCl815GR
I
FI LTER UNJT
L - - - - - - - - - -
"'
"'
�
�
@
It
3
IF U NIT
(PB-1 704C )
The I F signal fro m pin
1 4
is fed t o the gate o f the
IF first mixer, Q4 0 ! ( 3 SK5 1 -03 ) .wh e re t h e IF signal
is heterodyned with a
1 9 . 74 7 5
M H z ±
6
f l o c a l sign al
d elivered from crystal oscillator 04 o s ( 2 SC 5 3 5 A )
a n d b u ffer am plifier 04 0 6 ( 2 SC l 8 l 5 Y ) , resulting
i n a signal o f
10.76
M Hz ±Lf.
The n e w l 0 .
76
M H z ±
6
f signal is fe d t hro ugh filter
X F4 0 1 to the IF first mixer Q4 0 1 ( 3 SK5 1 -03 ) ,
where the fil tered signal is hetero d y n e d with a
1 9 . 747 5
M H z ±Lf sign al , prod ucing an
8 . 9 8 7 5
M H z
signal , the s a m e a s t h e original I F . This process
moves the IF signal across the p assband of XF4 0 1 .
The c ombination o f filters X F 3 0 4 and XF4 0 1
provides continuously variable width o f the I F
p ass b a n d .
T h e frequency o f crystal oscillator Q4 o s i s varied
b y varactor diode 0 4 1 o ( 1 S 2 209 ) .
O n t h e A M a n d FM m odes, t h e I F signal i s p assed
through diode switches 04 0 2 and 0 4 0 3 ( 1 S 1 007 ) ,
a n d d o e s n o t p ass t hrough filter X F 4 0 1 .
14
AM
030 4
2SK l 9 GR
13 SSB
16 1 2V
R327
2 . 7 K
- - -
-
7
4
N .B RXl2V S I G IN T X l2V
F M
-2 1 -