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~~M~!~ATIONS
S.,AItI
DIVISION
opening its source-to-drain path,
thus opening the signal path.
Otherwise,
a ground is applied to the gate via RIIJ, keeping Ql04 in an "on" condition.
Clll and RIIJ serve to lengthen the pulse
at the
gate
of Ql04
to
ensure
positive blanking.
FILTER BUFFER, FILTER, AND POST FILTER AMPLIFIER
+IO.5V
TO
0108
RI19
L10Z
CII9
.r
Il,~
. .
LIOI
FILTER BUFFER, FILTE'R, AND
POST FILTER AMPLIFIER
RIIS
+IO.5V
CII5
~
C1I3
>It-+--H..
FROM
TIOZ
From Tl02, the signal is
coupled to filter buffer amp-
lifier Ql05 via blocking cap-
acitor
CIIJ.
Bias
is
dev-
eloped
by
Rl15 and Rll?, wh-
ile emitter resistor
Rl16 is
unbypassed,
providing degen-
eration.
Output is taken ac-
ross collector load LIOl and
coupled through blocking cap-
acitor Cl14 to the first I.F.
filter,
FLI01.
Rl18,
CI08,
and
Cl15
are
a
decoupling
network.
From
filter
FLI01, the
signal is coupled through C-
116 to the base
of post fil-
ter amplifier Ql06,
which is biased
by
R120 and R121.
In the transmit con-
dition,
Ql06 acts as an emitter follower (discussed in detail in the Trans-
mit section
of this manual),
while in the receive condition, the output is
taken from the collector after being developed
across load LI02.
Cl18 is a
blocking capacitor.
Note that the use of inductive loads and unbypassed em-
itters in the stages preceeding the AGC attenuator ensure good strong signal
handling capability.
AGC ATTENUATOR
From QI06, the received I.F.
signal
is coupled through
Cl18
and R12J
to
AGC
attenuator PIN
diode CRI02,
and thence via C120
to
gate one of
pass band tuning
first mixer,
Ql08.
AGC voltage,
when required,
is applied to the
base of AGC driver QlO? via volt-
age divider
R129-RIJO·.
Current
is then supplied to the PIN diode
via R124 ,
causing it to
conduct
to a degree determined by the AGC
voltage;
it acts, in conjunction
with R12J,
as a variable voltage
divider,
similar in effect
to a
conventional volume control,
and
thus provides
the AGC action re-
quired.
Up to about 50 dB of at-
tenuation
is
available
at this
point.
ASC
I1
C12!l
TO PeT
. . - . . . . . - IT
FILTU
I.
C124
f-J'\A/'............
--1HH----J .,
'='
~"A
---,
TO QIO.
1.F.
AGC ATTENUATOR AND
PBT
II!
MIXER
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