HP 8340b User Manual

The
other outputs
of
the
A49
phase
detector
are:
•
FM
Coil
Drive
—
The
high
frequency
(>100
Hz)
phase/frequency error
voltage
is
output
to
the
YO
FM
coil.
•
High
Unlock
YO
—
Outputs
a
TTL
high
when
the
YO
loop
is
unlocked.
The
status
of
the
YO
loop
is
monitored
by
the
instrument
microprocessor.
•
Low
Overmod
—
Outputs
a
TTL
low
when
the
phase
difference
between
the
sampler
IF
and
the
20-30
synthesizer
is
greater
than
approximately
300°.
Frequency
Modulation
A23
FM
Driver.
This
assembly receives
the
±
1V
or
±
8V
frequency
modulation
input
from
J22
on
the
front
panel.
Frequency
modulation
voltage
information
is
converted
to
a
corresponding
current
that
goes
directly
to
the
A44
FM
coil
via
the
A62
motherboard and
A44A1 YO
bias
assembly.
The
FM
driver
outputs
a
low
signal
(LOMD)
if
the the
peak
deviation
of the
FM
input
signal
exceeds
10
MHz.
SWEEP
GENERATOR
-
YO
LOOP
FUNCTIONAL
GROUP
THEORY
OF
OPERATION
This functional
group
can
best
be
described
by
considering
the
two main instrument
modes
of
opera¬
tion:
CW/manual,
and
swept
frequency.
The
swept
mode
can
be
in
one
of
three
conditions:
single
band
sweep,
multiband
sweep,
or narrow
band
sweep.
CW/MANUAL
Sweep
Operation
When
either
mode
is
selected,
the
sweep
generator/YO
loop
circuitry
phase-locks
the
YO
at
the
appropriate
frequency.
The
instrument
microprocessor
addresses
and
sends
a
number
to
the
A54 YO
pretune/delay
compensation
assembly,
which
produces
a
proportional
voltage,
VDAC.
VDAC
is
sum¬
med
with the
constant
DC
voltage,
VREF,
producing
PRETUNE
-
a
voltage
that
tunes
the
YO
to
approximately
the
desired frequency
(i.e.
to within
the
capture
range
of
the
YO
phase-locked
loop).
VSWP
makes
no
contribution
to the
PRETUNE
voltage
in
CW
operation.
The
processor
also
sets
the
frequencies
of
the M/N
and
20-30
synthesizer
loops according to
the
CW
frequency selected.
The
outputs
of
these
two loops
are
used
by
the
YO
loop
to
exactly
tune
and
phase-lock
the
YO.
The
A45
directional
coupler
couples
a
portion of
the
YO
RF
output
back through
a
low-pass
filter
to the
A48
sampler,
where
it
is
mixed
with the
Nth
harmonic
of the
M/N
output.
This
generates
a
difference
signal.
Sampler
IF,
in
the
range
of
20-30
MHz
that
is
input to
the
A49
YO
loop
phase
detector.
There
the
phase
is
compared
to the
20-30
MHz output
signal.
The
resultant
error
signal,
YO
TUNE, phase-locks
the
YO.
The
high
frequency
portion
on
YO
TUNE
(>100
Hz)
is
applied
to the
YO FM
coil by
the
FM coil
driver
on
the
A49
YO
loop
phase
detector
assembly.
The
low
frequency
portion (<100
Hz)
is
summed
with
PRETUNE
on
the
A55 YO
driver
and applied to
the
YO
main
coil.
This
completes
the
YO
loop
and
phase-locks
the
YO.
Manual
Sweep
operation
is
identical
to
CW
in
the
operation
of the
sweep generator
and
YO
loop
circuitry.
D-4 Sweep Generator
-
YO
Loop Theory
of
Operation
HP
8340B/41B

HP 8340b Specifications

General

Brand	HP
Model	8340b
Category	Inverter
Language	English