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OCUBIC
COMMUNICATIONS
5111111_
DIVISION
FWD and REFL signals from the watt-
meter board are also applied to,
SWR
me-
ter drivers UI04A and Ul04B through cal-
ibration
potentiometers R147 and
R149 ,
respectively.
These are unity-gain amp-
lifiers,
used only to prevent the meter
from loading the wattmeter board output.
The operator may
select either the FWD
or
REFL
power to be read on the cali-
brated meter
by
means of the front panel
METER
switch.
Rl48
and
R150 are cur-
rent limiting resistors.
VOX
CIRCUIT
+IO.5V
"'44
VOX DELAY
+
+ev
1---+-0 JII4
CIl8
~
RI46
+
~C128
+8V
R14'
'='
PTT
r
RI47
CRIIS
RI48
RI43
CR 114
RI42
.....-
.........--.NI./'---o
+8V
+
CI30
vox
DELAY
ANTI-TR'P
RI49
-=
CRII5
SWR
METER DRIVERS
-!lV
VOX GAIN
RI40
RXA
R.38
VOX
AMP
a
COMPARATOR
F"OIil
CI24Q-~+--....-oII~
When
vox
operation is selected
by
the operator, microphone
AF
is supplied
from the preamplifier to UI04A, where it
is further amplified. The amount of this
amplification
is controlled
by the
VOX
gain control,
Rl40.
The output of
this stage
is rectified
by
CRII), and smoothed
by
C125, and applied to the
inverting input of
comparator
UIo4B.
A sample of the
received
AF,
from the speaker line,
is
applied
to the anti-trip con-
trol,
Rl49 ,
and then
through
Cl30 to CRl15
and CRlI6, which
form a voltage
doubler recti-
fier.
Cl29
smooths this
IX:
signal,
and i t is
coupled to
the non-inverting input of the
comparator • A
IX:
bias,
to set
the comparator 's threshold,
is
added to the
rectified
anti-
trip
signal by the RI46-Rl48-
network.
The comparator's
output
will depend
upon
which
of the two
input
signals
are
the larger; should the
VOX
sig-
nal
be
the largest, the output
will go
low; if the anti-trip signal is larger,
it will be prevented from doing so.
The
output of
the
comparator is
coupled through R142 to the trigger in-
put of timer UI05,
causing it to acti-
vate and
its output
to go high.
This
high state is
continued for the durat-
ion of the low on the
input (diode CR-
114 prevents C128 from charging during
the duration of the
low voltage at its
cathode) plus the time
it takes for C-
128 to charge through
Rl44 and R145 to
2/3 of the supply voltage after the low
6-6
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