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+IV
o
Rl78
RIOl
CIC!)
I------::-:-~Hq.
IF ûUl
f
RI73
FRaM
"""' 1
f--"VV'v+e+-...-AAfV--<PA SlA 5
CONTROL
Ll~E
L.o.
AMPLIFIERS
8
I g MIXER
RX tN
JIl~
()---j
fr~O:M~E'
CI02
L 0
IN
OCUBIC
I
COMMUNICATIONS
SMlAIfI DIVIBION
R164 and R165.
While the former is
bypassp.d in
the usual manner,
the
latter is not,
and a
signal suit-
able for
driving the display freq-
uency counter is
taken from across
it, via R166 and c16J.
Arnplified L.O. output is taken
from the
collector of Ql14 and co-
upled to the base
of Ql15.
Again,
bias is conventional,
being devel-
oped by Rl?l and R172.
The
output
of Ql15 is taken across its emitter
resistor,
Rl?J, via C16? and R174,
and coupled
through
R17? and c168
to the
base of
mixer driver QI01.
The
P.A. Bias control line is high
in the receive condition,
thus re-
verse biasing CRI04, preventing the
L.O. signal
from being
shunted to
ground by C169,
as it would
be in
the transmit condition.
I
Bias for Q10l is developed
by
RI04 and RI07, and CI04-RI06 form the us-
ual emitter circuit.
CIOJ and RI05 form a feedback network,
which, in con-
junction with Rl?? and Rl?4 set the gain
of QI01.
For a more complete dis-
cussion of feedback amplifiers and the1r operation, refer
to the "Servicing
Hints" section of this manual.
NOISE BLANKER GATE
CIII
N.B. PULSE
FIR5T
I.F.
AMPLIFIER
a
NOl5E BLANKING
GATE
RII4
+IO.5V
Ril'
RI12
FROM
CIO ... 6 ......
r-+-I
ZIOI
>-i
The output of the first
mixer, ZlOl, now at the I.F.
frequency, is coupled to the
first I.F. amplifier,
QIOJ,
via blocking capacitor cl06.
Rlll and
Rl12 form the bias
network, while
emitter res-
istor
RIIO
is
unbypassed,
providing some
degenerative
feedback.
Output is
devel-
oped across a parallel-tuned
resonant circuit composed of
the primary of TlOl and CI09.
Rl14 and CIO? form a decoup-
ling network, while the lat-
ter also
places
the upper
end of the pr1mary
of
nOl
at AC
ground,
so that CI09
is effectively
in
parallel
wi
th TI01.
The secondary
of TIOl
presents a
signal at low impedance,
which
is
coupled through noise blanker gate
Ql04 to the primary of TI02, where it is
stepped back
up.
Cl12 resonates
the secondary of Tl02.
When the noise bl-
anker circuit detects a noise pulse of sufficient amplitude,
the gate of Q-
104 is fed a positive pulse through CRI01,
effectively cutting it
off and
3
·4
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