HP 8340b User Manual

RF
Section
Theory
of
Operation
The
RF
section
contains
the
microcircuits
and board assemblies
that
produce,
amplify,
and control
the
RF
output.
Refer
to Figure
H-2
for
a simplified
RF
functional
group
block
diagram.
RF
power
generated
by
the
YIG
oscillator
is
delivered
to the
mod/splitter,
which
couples
off
a
portion
of
the
signal for
the
rear
panel
auxiliary
output.
The
mod/splitter
also
splits
the
power
to provide
RF
to
the
high
band
power
amplifier,
and
the
low
band
mixer.
LOW BAND
Low
band
is
produced
by
mixing
a
high-power swept
LO
signal
with
a
fixed
RF
signal.
The
fixed
signal
is
generated
by
the
3.7
GHz
oscillator,
and
passes
through
a
linear
modulator, pulse modulator,
low
pass
filter, and
isolator,
before
it
reaches
the
mixer.
The
mixer
output
frequency
(IF)
is
the
difference
between
the
LO
and
the
RF
frequencies.
Because
the
LO
sweeps
from 3.71
to
6.0 GHz,
and
the
RF
is
fixed at
3.7 GHz,
the
IF
sweeps
from
0.01 to
2.3 GHz.
The
low
band
power
amplifier
amplifies
the
IF,
and
sends
it
to
the
low
band
splitter/detector, where
a
small
portion
of the
signal
is
split off
and detected
for
leveling.
The leveled
IF
(RF)
enters
the
SYTM
(switched
YIG-tuned
multiplier),
which
provides
a
straight
through path
for
RF
from
the
low
band splitter/detector
when low
band
is
activated.
After
passing
through
the
SYTM,
the
signal
passes
through
the
directional
coupler,
which
performs no
function
in
low
band,
and
the
step attenuator,
before reaching
the
instrument output
connector.
HIGH
BAND
The
high
bands
are
produced
by
feeding
the mod/splitter
RF
output
through
the
high
band
power
amplifier.
The
SYTM
generates
harmonics
from
the
high
level
output
of
the
power
amplifier,
to
pro¬
duce bands
2
through
4.
The
SYTM
contains
a
bandpass
filter
tuned
to the
desired
RF
output
fre¬
quency,
which
allows
it
to
pass
the desired
RF
output
frequency,
and reject
the
unwanted
harmonics.
The directional
coupler couples
off
part
of the
SYTM
RF
output
to
the
high
band
detector for
high
band
leveling.
The
step attenuator provides
low
power
output
levels
in
all
bands.
LEVELING
The
ALC
(automatic
level control
circuit)
uses
feedback
to
hold
the
RF
output constant
throughout
the
full
frequency
range.
When
internally leveled
in
high
band,
voltage from
the
high
band
detector
is
fed
through
a log
amplifier
and
summed
with
a
correction
level that
closely
approximates
the
variations
of the
RF
attenuator
and
the
RF
cables.
The
corrected
detector
level is
then
fed
through the
sample/hold,
and
routed
to
the
linear
modulator driver assembly
where
the
corrected detector voltage
is
summed
with
the
reference
voltage
at the
integrator
input.
H-2
RF
Section Theory
of
Operation
HP
8340B/41B

HP 8340b Specifications

General

Brand	HP
Model	8340b
Category	Inverter
Language	English