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OCUBIC
COMMUNICATIONS
SMrAIfI
DIVISION
by
the R611-R614 combination.
Output is taken via low pass filter C614-L604
-C615 to assure good spectral purity.
When operating in the USB mode, the
required frequency shift is set
by
c608, which is switched in parallel ·with the tuned circuit by CR602.
When RIT is used, the required shift is obtained
by varactor diode CR-
601, connected in parallel with the tuned circuit
by
blocking capacitor C602.
The DG
tuning voltage for this varactor
is applied
through the R601-R602
combination, and is decoupled by C601.
c606 is a calibration control.
PrO SWITCHING
+eV
"
PTO ", ....
OUT
PTO SWITCHING PIN
DIODE DRIVERS AND
RIT SWITCH
:I:.
~
R517
C5I7
L..------Hi..---o
Ta..~
-- - -
L!102
PTO A SWITCH AND
PTO BUFFER
RlS27
1t531
"R· LINE
R524
R522
FROM
C5IB
PTO A
C>-l
t-J\R"'521/'1
~HfJ'RI/'51"9 ~t-t
If-",IV'.,.............
--+.f
CR503
RIT
SWIITCHo---+-.-I._~
The switches
are used
for the
PrO
outputs; only
one will be described here,
as bath are
identical
and
the description of one will
apply equally to both.
A control voltage, the
generation of which will be
discussed later, is applied
to decoupling
RF
choke L502
from Q504.
C519,
C515 and
C516 are bypass capacitors.
This voltage
is applied to
PIN diode attenuators CR503
and CR504 through isolating
resistors
R520 and
R51?,
causing the diodes to pre-
sent a
low resistance
to
ground.
Since
the
signal
from the PTO passes through
R521 and R519 (as
weIl
as
blocking
capacitors
C518
and C51?, it is dropped
by
these
two resistors,
with
essentially
none
passing
through to the
base of the
buffer,
Q505.
Thus,
when
this control voltage is re-
moved, the PTO
output
is
allowed to pass to the buf-
fer.
Q505 is a summing am-
plifier, with its
gain de-
termined
by
the
ratio
of
R512
to R518
(and others,
when the
other
section is
in use).
Bias and
emitter
circuitry are conventional,
and
output
is
taken from
the collector
through low
pass filter
C51.2-L503-C513
to assure that no harmonies
or
spurs
are passed on to
5-4
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