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OCUBIC
COMMUNICATIONS
S_AItI
DIVIBIDN
the mixer.
In the off condition, the switch provides greater than 100 dB of
attenuation to the unwanted PTO output.
The control signal
for the PTO switching circuitry is derived from the
front panel PTO switch.
In the PTO A position,
+8 volts is applied to the
PTO B switching circuitry directly through the switch contacts, thus disab-
ling PTO B.
It is also applied to the base of Q50J, causing it to saturate;
since Q504 is direct coupled to its collector, the latter is then turned off
and no voltage appears on the
PrO A control line,
allowing its
signal to
pass and appear at the output.
In the PTO B position,
no voltage is applied to the PTO B line, allow-
ing it to function, and Q504 is turned on, allowing voltage to appear on the
PTO A control line, disabling PTO A.
For split operation,
"R" line
voltage is used (through the PTO switch
on the front panel) to drive
the PrO B control line
and the Q50J-Q504 com-
bination.
Thus, which PTO is turned on depends upon whether the "R" line is
high or low (receiver
on or off).
For reverse
split operation
Q501
and
Q502 provide
an inverled
uR"
line voltage
(+ for transmit, 0 for receive)
which is used instead.
When the RIT switch on the front panel is on, and the'transceiver is in
the receivé
condition ("R" line high), AND gate U502A is on, and its output
is high.
This high is
coupled to one input
of U502B and U502C.
The other
inputs of each
of these
AND gates is connected to the PTO A and PTO B con-
trol lines,
respectively.
Thus,
when the PTO B control line is high (and
the PTO A line is low) ,
analog switch U50JA
is turned on and the voltage
from the RIT control wiper
is applied to the
RIT input of PTO A.
R5J6 and
R5J7provide center adjustment for the RIT circuitry in the PTO.
When the PTO A control line
is high,
the remaining section of the AND
gate is on, turning on U50JB, and supplying the RIT control voltage to PTO B.
A center adjustment similar to that for the A PTO is included in the circuit
although not shown in the diagram, for simplicity.
LOC
AL
OSCILLATOR MIXER
+BV
5-5
L.O,
MIXER
RI62
RI63
I.
RI64
RI65
TO LO
BAflIOPASS
FILTER/BUFFER
-
AMPLIFIERS
CI72
RI58
RI61
RI6ü
0111
CI6B
FROM
RI59
<>-I
f-J\."""r-.-----l,..-i
vco
CI69
BUFFERS
Output from the band synthe-
sizer (VCO buffer) is
applied to
mixer driver Qlll through
block~
ing
capacitor
C169.
Q111
is a
feedback amplifier whose gain de-
pends
on
the
ratio
of R160 to
R159,
and its output
is applied
to one input
of the
L.O. mixer
ZlOl,
which is a doubly-balanced
mixer identical to others used in
this transceiver.
Also, the out-
put
of the
selected PTO
is ap-
plied to
Q112
through blocking
capacitor C175.
This stage
too,
is a feedback amplifier, with its
gain determined
by
R167 and R168.
lts output
is similarly
coupled
to ZlO1-
Output of ZlOl is at the op-
erating frequency plus 9 MHz, and
"
1tI
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