Filter Buffer, Filter - Swann CUBIC ASTRO 102 BX Service Manual

OCUBIC
COMMUNICATIONS
S""AIfI
DIVISION
TO
0108
RII9
QI0 ... 4 -1-_ _
' f t
l,,~"
"' "
R 116
RII4
LIOI
RII8
Ril I
+10.5V
RI12
CI08
F
+10.5V
FIR5T
I.F.
AMPLIFIER Sr
NOl5E BLANKING GATE
CII5
J(
RII7
collector load LIOl and coupled through
IF filter, FLIOl. Rl18, CI08 and Cl15
+I0.5V
CII3
>-1 ....
--+-1.
FROM
Tl02 IlItI5
FROM C101-6-6-4-I
ZIOI
>-i
The secondary of TlOl pre-
sents a signal at low impedance
which is coupled through noise
blanker gate Ql04 to the pri-
mary of Tl02, where it is step-
ped back up. Cl12 resonates
the secondary of Tl02. In the
transmit condition, the noise
blanker gate is held in the on
condition at all times.
FILTER BUFFER AND FILTER
From Tl02, the signal is coup-
led to the filter buffer amp-
lifier, Ql05, via blocking
capacitor Cl13. Bias is de-
veloped by Rl15 and Rl17, wh-
ile emitter resistor Rl16 is
unbypassed. Output is taken across
blocking capacitor Cl14 to the first
are a decoupling network.
From filter FLIOl, the
signal is coupled through Cl16
to the base of post filter amp-
lifier Qlo6, which is biased
by
voltage divider R120 and R-
121. In the transmit condition
Qlo6 acts as an emitter follow-
er, with its output coupled via
C180 and R197 to the transmit
mixer driver, Ql19.
TRANSMIT MIXER
r-----------~J_O
TI.'
TX MIXER, DRIVERS
As mentioned above, the
signal from the post filter
amplifier, Qlo6, which is now
a single sideband, suppressed
carrier signal at the IF freq-
uency of 9
MHz,
is coupled to
transmit mixer driver Ql19.
This stage has conventional
bias, an unbypassed emitter,
and its output taken from the
collector through a winding of
Zl02. This winding is de-
coupled
by
R196 and C179. Bias
supply comes from the T/S line
from the control circuitry,
1O.1IV
+'O.lIV
4-3