HP 8340b User Manual

20-30
LOOPS
The 20-30
loops contain
three
phase-locked loops
used
together
to
provide
the
YO
loop
with
1
Hz
CW
resolution,
and
with
analog
sweep
widths
from
100
Hz
to
5
MHz-
For
sweep
widths of
5
MHz
or
less,
the
YO
Loop remains
phase-locked during
the
sweep,
and
the
20-30
Loop
is
swept
the
desired
amount.
For
sweep
widths
greater
than
5
MHz,
all
phase-lock
loops
lock
at the
beginning
of
sweep,
the
20-30
Loop remains
fixed,
and
the
YO
is
swept.
This
is
called lock
and
roll,
and
will
be
discussed
later.
The 20-30
loop
generates
an
output
between
20
and
30
MHz
in
CW
mode,
and
between
15
and
30
MHz
when
swept.
This
loop
has
an
output resolution
of
1
Hz.
Comparing
and
locking
the
down-
converted
YO
frequency
to
the
20-30 output
produces
a
1
Hz resolution
in
the
YO
frequency.
YO
LOOP
The
YO
Loop
contains
the
YIG
oscillator
(YO),
which
is
the
tunable
local
oscillator
source
for
all
frequency
bands.
When
the
instrument
is
set
to
a
specific
CW
frequency,
the
instrument processor
sets
the
frequency
of the
M/N
and 20-30
loops
accordingly.
The
instrument
processor
also
sets
the
YO
pretune
voltage,
which
tunes
the
YO
to
the
approximate
frequency.
The
output
of the
YO
is
fed
through the
A45
directional
coupler
to
the RF
section.
The
directional
coupler
splits
off
part
of the
YO
signal,
which
goes
to
the
sampler.
The
M/N
output frequency
and
its
harmonics
are
mixed
with
the
YO
frequency
in
the
sampler
to
produce an
IF
signal
between
20
and
30
MHz.
The
20
to
30
MHz
IF
from
the
sampler
is
compared
to
the
20-30
loop
output
in
the
phase/
frequency
detector.
The
error-induced voltage
from
the
phase/frequency
detector
is
fed
through
a
sample/hold
circuit and
is
summed
with
the
pretune
voltage
that
drives
the
YO
tuning coils.
The
YO
frequency changes
until
the
output
voltage from
the
phase/frequency
detector
goes
to
zero
and
phase-lock
is
achieved.
For
sweep
widths
greater
than
5
MHz,
the
YO is
phase-locked
at
the
start of the
sweep.
The
sample/hold circuit
is
then
set
to
hold, breaking
the
loop,
and allowing
the
YO
to
sweep.
The
sweep
generator
initiates
a
voltage
sweep
(VSWP)
ramp
that
is
summed
with the
YO
pretune
voltage.
This
voltage
causes
the
YO
to
sweep
to
the
STOP
frequency.
This
action
is
referred to
as
Lock
and
Roll.
During
multi-band
sweeps,
the
YO
phase-locks
at the
start
of
each
band
before
continuing
on
with
the
sweep,
ensuring
frequency
accuracy
at
the
beginning
of
each
band.
/
CONTROLLER SECTION
The
controller
section
performs
all
data
transfer,
and
coordinates
the
control
signals
that
operate
the
I
instrument.
It
contains
a
16-bit
microprocessor,
a
total
of
64K
X
16
ROM
and
8K
X
16
RAM.
This
section also
contains
interface circuitry for
communicating
with
the
rest
of the
instrument.
Digital
information
is
exchanged between
the
microprocessor
and
other
sections
of the
instrument
on
a
bi-directional
bus.
At
power
on
instrument
preset,
the
controller
runs
through
an
instrument
self-
test.
The
microprocessor
also
sets
the
front
panel
controls
to
preset
conditions
if
instrument
preset
was
pressed.
HP
8340B/41B
Change
7
Assembly-Level
Service
Overall
Instrument
Theory
A-5

HP 8340b Specifications

General

Brand	HP
Model	8340b
Category	Inverter
Language	English