3-1
-3 RF CIRCUIT (RF UNIT)
The RF
circ
uit ampUlies slgnals within the range
ol
Irequency coverage and filters out-ot-band signaIs.
The RF ampliliers
(al
-a4
) employ gallium arsenic
FIT
s
(35K121). The combinatIon ol the RF amplifiers and
tuned bandpass filters expand the dynamic range and
enhance the sensitivity tor the high frequency. Each
tuned amplifier has a
pp
roxi
ma
tely 10 dB gain.
06
......
0 10 employ varactor diodes which are controlled
by the PLL loek voltage. The voltage is
curr
ent-ampüüed
at the
OC
am
plil
ier circuit (IC3a, ICl a) and is then applied
to
the varactor diodes. These varactor diodes tune
the
ce
nter trequency of an RF passband tor wide bandwidth
receiving and 9000 image response rejection.
D50 prote
ct
s the varactor diodes trom being charg
ed
over their maximum voltag
e.
1C4
lunetions
as a comparator and is
co
ntrolled by the
BPF4 signal line. Pin 1 of 1C4 outputs positive voltage
in a frequency range of 5
12-1024
.9999 MHz,
whiJ
e pin 7
of
1
C4
outputs positive voltage In a frequ
enc
y range of
25
.oooo-
51
10
9999 MHz.
IC5 switches the power source of
BPF1
- B
PF
4 ON
or OFF by using "Bl - B4" and " BH" signals from the
LOGI
C UNIT. 0 21 and
05
2
pro
vide the converted and
stabie voltage to
IC5
.
The 2
5-
1024.9999 MHz slgnals are applied to four
separate filters through switching diodes (
05
, 0 12, 0 19,
011, 0 18, 025) depending on the range of frequency
co
verage. The relay circuit (RL1,
RL
2) Is used instead
of switching diodes tor the
fr
equencies above 512 MHz.
This device prevents a diode trom causing distortien
wh
en r
ece
ivlng very strong signais.
(1) BPF1 (25.0000
-89
.9999 MHz)
The 25.oooo
-89
.9999 MHz signals pass through a parallel
resonant circuit (
06
, L
11
, C15) to suppress ha
lf
of the
reeeive freque
ncy
in
terfer
e
nce
signals
an
d are then
applied to an
RF
amplifier (
01)
via a tuned bandpass
filter (
07
, 0 8, L12
-L
14). The amplified signa!s are
applied to a 2nd RF amplifier (
07)
through a tuned band-
pass filter (Dg,
010
, L16
-L1S
).
(2) BPF2 (90.0000
-249.9999
MHz)
The 90
.0000-2
49.9999 MHz signals pass Ihrough a
parallel resonan, circuit (
013,
L22, C25)
to
suppress
half of the
recei
ve
freque
ncy
interference signaIs and are
the
n appli
ed
to a series resona
nt
circuit (0 14, L70, C6
1)
to suppress streng signals in a frequency ran
ge
of
BO-
110 MHz, sueh as FM and TV broadcasting stations.
The signals are applied to an RF amplifier (
02)
via a
tuned bandpass lilter (0 15, L23
-L2
5, C
11
9). The ampli-
li
ed signaIs are applied to a 2nd RF amplifier (07)
through another tuned bandpass filler (0
17,
L27-
L2
9,
C1
20).
01 3
-015
and 0 17 employ varactor diodes whlch are
controlled by the PLL lock voltage. The voltage is
current·amplified at lhe OC amplifier circuit (IC3a, ICl b)
and is then applied
to
the varac
tor
diodes. These varactor
diod
es tune the c
enter
Ir
equen
cy
of an
RF
passband
lor
w
id
e ban
dw
idth reeeiving and
goOO
image response
re
jection
.
0
51
protect
s
varae
tor diodes
Ir
om being negatively
charged.
o RF CIRCUIT
10
FIL1
fFl
l 2
UN
I
_,
25.0000 89 9999MHz
-
•
..
,.
1\
Ql
AF
"'""
I
~!
I
ICB
I
omp
OB-
""!'
r-,
i%
I
r-,
I
~
•
34
I
I
l-;;.
«
,
I
I
I
L
__
.
__
.J
I
178.1
....,
I
1291
.1MHz
BPFZ
I
I
9O.
0000
-
2I
9.9999MHz
••
Q'
I
I
,DI1
LPF CONT
I
'"~
LD
I
I
C3b
I I
\~
OB
I
I
I
BPF
3
cv lI
ne
L_
___
....J
trom
2SO
.0000-511.9999MHz
VCO
UNIT
• •
Q3
••
l
LD
p:(I
~
Uoe
024
'rom
P'
OOU
BL
UN
IT
N:1C
CONT
AGC
II
n.
0
20
'
rom
BPF
4
MAIN
UN
IT
512..
~
.9999M
HZ
\"'&0/
AF
UN
IT
.
PFCONT
CVllne
IC1,1C2
"
om
VCO
UN
IT
',om
ATT
clrcu
ll
FIg. 2
3-2
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