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Sencore CB42 - SSB Transmitter

Sencore CB42
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SSB
TRANSMITTER
lIooIanc.
Control
-
-
"
Input
Fill.
19-5impli(ied
SSB buklllced moduwlor.
The
heart
of
an SSB transmitter
i.
a "Balanced Modu.
lator".
The
balanced modulator
is
a bridge
ci~uit
with
an
audio
input
and an
RF
input. A simplified
balanced
modulator
i$
sbown in Fig.
19
•
The
function
of
the
balanced modulatO!" is
to
produce
both
the
upper
and
lower sidebands when
the
audio modula.
ting
signal and
RF
signal
are
inje<;wd
at
their
~spee·
tive inputs.
The
balance control is adjusted until
the
RF carrier is
completely
canceled
in
the
bridge.
Fig.
20
shows how
the
balanced modulator
is
used in
a typical
SSB tranamitter. This example typifies
mOllt
SSB transmitters which use a frequency
lower
than
the
carrier frequency
to
operate
the
balanced
modu.
lawr.
This simplifies
the
design
of
the
balanced
mod·
ulawr
since
it
operates
at
a lower frequency.
upper
and lower sidebands
p~sent.
To
seled
the
pro-
per sideband,
the
output
of
the
balanced
modulator
is
fed
to
a filter
that
removes
the
unwanted
.ideband.
At
this point. we have
an
SSB signal
with
a
sup.
pressed carrier
of
7.8
MHt.
This signal is applied
to
the
input
of
the
transmit
mixer
which opera/.e$
the
Jame as a receiver mixer
except
we are raising
the
frequency instead
of
lowering it.
The
output
of
this
mixer
is
the
desired
RF
frequency.
The
output
of
the
transmit mixer is
fed
to
several
stages
of
linear amplification,
Bnd
finally to a low·
pass
filter to eliminate any harmonic
content
that
has
boon
created
in
the
mixing processes.
The
output
of
the filwr is fed to
the
anwnna
for transmission.
The
output
of
the
balanced
modulator
has
both
the
t
"
Mcasu,e
PEP
F,.q.
Us. Scope Converte,
Mea.",e
F,equency
J
RF
Volt.ge
..
~
RF
TVI
Amp
Filte'
I
••
USB
AM
LSB
....
Inject
Audio
24

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