Cubic SWAN SS-15 - Page 31

BALANCED
MODULATOR
-
A
four
diode ring
modulator is used
for the
balanced
nodulator.
The two
inputs to the balanced
nodulator are
the carrier
oscillator
output and either
the audio
output
frorn the
speech
arnplifier
or
DC frorn the
CW drive.
When balanced,
1o
out-
plt
of any
kind is
present at the
modulatorrs
output
transformer.
When audio is
present at its
input, the
output
of the
balanced
nodulator is
a-double sideband
signal
without
an
RF
carrier.
If
CW is being
transmitted,
the
CW
DRIVE control
unbalances
the
rnodulator
causing an RF
carrier
at the
output.
XTAI
FITTER
-
The
crystal
filter narrows
the
IF
passband to 2.7
KHz.
The
filter is
used
to
select
the
desired
sideband
which is
positioned
in
the
filter
passband
by
selecting
a
5.5000
MHz
(NORM)
carrier
frequency
on
the
lower
skirt
of
the
selectivity
or a
5.5033
MHz
(OPP)
carrier
frequency on
the upper
skirt.
Figure
6
shows typical seLectivity
curves
including
those
for both
the
standard
and SSl6B Swan
filters.
FIGURE 6
-
26-