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Digital
Control
Section
Operational
modes
and
internal
functions
of
the
spectrum
analyzer
are
selected
and
controlled
directly
from
the front panel.
The
modes
anO
tunctions
that
are
selected
are processed
and
activated
by
the
instrument
master
microcomputer
which
tarks
and
iisten"
to
ail
cir_
cuits
over
the
instrument
bus.
ttre progiammable
ver_
sion
can
also
be remotely
controlled
frim
an
external
controiler
through
the
IEEE_4gg
(GplB)
connector.
This
connector
interfaces
to
the
instrument
microcomputer
through
the
GptB.
Front
panel
control
and
sel€ctor
data
is
processed
by
a
front
panel
CpU
that
interrac""
*itt
the
master
microcomputer
over
the
instrument
bus.
The
master
microcomputer
receives
and
sends
all
of
its
information
over
the
instrument
bus
to
th€
intemal
circuits.
The
programmable
version
communicates
with
other
instru-
m€nts
through
the
GplB
connector.
The programmable
control
language
corresponds
to
tront_panel
controfs.
Theory
of
Operation
-
4g4A/4g4Ap
Servlce,
Vol.
.l
Power
Supply
Section
The
power
supply
s€ction
provides
regulated
dc
power
and
forced
air
cooting
for
all
circuits
within
the
instrument.
The
switching
suppty
is
capabte
of
provid-
ing
regulated
voltages
over
a
wide
range of
input
line
frequencies
and
voltages.
The
cooling
system
consists
of
an
intake
on
the
bottom
of
the
cise, air passages
within
the instrument,
a
fan,
and
a rear
panel
exhaust.
Air
is
routed
to
all
sEctions
of
the instrument
in
propor-
tion
to th€
heat
generated
by circuits
within
thoie
sec-
tions.
Internal
temperature
variations
are
minimized
to
provide
reliable
operation.
Other
Sections
Interconnections
between
assemblies
are
made
through
a
common
Mother
board.
Most
circuit
board
assemblies
plug
into
the
top side
of
the Mother
board.
Assemblies
on
the
RF
deck
are
connected
to the
bot-
tom
side
of
the
Mother
board
through
cables
and
con_
nectors.
7-3