HP 8340b User Manual

A23 FM
Driver
Theory
of
Operation
The
front
panel
FM
input
can
accept an
AC
signal
that
is
sent
to
the
A23
FM
driver.
This
signal
can
be
of
two
different
ranges:
±
8
Vac
in
1
MHz/V
FM
sensitivity
or
±1
Vac
In
10
MHz/V
FM
sensitivity.
The
FM
driver
scales
this
signal
and
converts
it
into
a
current
that
drives
the
YIG
oscillator's
FM
coil.
The
FM
Driver provides:
•
FM
input
range
attenuation
•
Harmonic number
(band
number)
attenuation
•
FM
overmodulation
detection
•
FM
coil
drive.
A44/A44A1 YIG
Oscillator/Bias
Assembly
Theory
of
Operation
NOTE: The
A44
microcircuit and
A44A1
bias
assembly
are
not
field
repairable
and
are
not
separately
replaceable.
The
FM
coil
In
the
instrument
is
connected to chassis
ground
at
the bias
assembly.
During
testing,
however,
the
coil
must
be floating
so
a
jumper
has
been provided
to
connect ground
after
testing.
YO
Switchable
Filtering.
The
filtering
required
at the
YO
main
coil
depends
upon
whether
the
instru¬
ment
is
in
the
CW
mode
or
in
swept
modes.
A
switch circuit
is
provided
to
accomplish
this
filter
change.
A
signal
from
the
processor
(HFIL)
goes
high
in
CW
mode.
This
signal
is
buffered
on
the
A50
YO
loop interconnect
assembly.
The
resulting signal
(LFIL)
goes
to
the
A44A1
YO
bias
assembly
where
it
provides
a
very
low
impedance
path
for
the
CW
filter
circuit.
The
CW
filter
is
connected
directly
across
the
YO
main
coil
in
CW
mode.
The filter
reduces
residual
FM
of
the
YO.
A
swept
mode
filter
matches
the
delay characteristics
of
the
YO
main
coil
to those
of
the
YO
main
coil
driver
circuitry.
Figure
D-l.
A44A1
YIG
Oscillator
Bias
Assembly
Drawing
HP
8340B/41B
Change
10
Sweep
Generator
-
YO
Loop
Theory
of
Operation D-9

HP 8340b Specifications

General

Brand	HP
Model	8340b
Category	Inverter
Language	English