HP 8340b User Manual

YO
Tune.
The
YO TUNE
voltage
is
generated
by
the
A49 YO
loop
phase
detector from
the
20-30 MHz
input
(from
the
20-30
loop)
and
the
Sampler
IF,
which
is
the
down-converted
product
of
the YO
RF
output
and
the
Nth
harmonic
of the
M/N
output.
The
A45
directional
coupler couples
a
portion of the
YO
output
back
through
the
AT2 15
dB
attenuator
and
A46
7
GHz
low
pass
filter
to
the
A48 YO
loop
sampler.
There
it is
mixed
with
the
Nth
harmonic
of the
M/N
output to produce
the
Sampler
IF,
that
is
in
the
frequency
range
of
20-30
MHz.
This
signal
and
the
one
from
the
20-30
loop
are compared
in
the
A49
YO
loop
phase detector.
The
resulting
error
signal
is
amplified and
integrated to
produce
YO
TUNE,
with
a
sensitivity
of
-3
MHz/V.
When
HLEY
(high
lock
enable
YIG
oscillator)
is high,
the
YO
loop
is
closed.
When
HLEY
is
low,
the
sample
and
hold
circuit
holds the
phase-locked
value
of
YO
TUNE
constant,
breaking
the
loop to
allow
a
voltage
ramp
(VSWP)
to
be
summed
into
PRETUNE
to
sweep
the
YO.
YO
FIVI
Coil
Drive.
The
A49
FM
coil
driver
has
a
100
Hz
high
pass
filter.
Only high
frequency
(>100
Hz)
portion
of
YO TUNE is
applied
to
the
YO FM
coil.
The
resulting
output
is
the
YO
FM
COIL
DRIVE
current.
The
low
frequency
portion (<100
Hz)
of
YO TUNE
is
summed
with
PRETUNE
and
applied to
the
YO
main
coil.
YO
Main
Coil
Drive.
The
YO MAIN COIL DRIVE
current
is
derived
at the
ASS
YO
driver from
the
PRETUNE
and
YO
TUNE
voltages.
The
ASS
YO
driver
sums
YO TUNE
with
the
OFFSET
voltage,
and
scales
PRETUNE
via
the
GAIN
adjustment.
The
YO
MAIN
COIL
DRIVE
current
is
constructed
as
a
linear
function of the
desired
YO
frequency.
The
OFFSET
adjustment
varies
the offset of
the
curve;
the
GAIN
adjustment
varies
the
slope.
These
two
adjustments
are
used
to
ensure
the
tuning
accuracy
of
the
YO
versus
PRETUNE
voltage
over
its
full
range
of
operating
frequency.
OFFSET
has
greater
effect
on
the
low
end
of
the
range
(2.30
GHz),
and
GAIN
has
greater
effect
on
the
high
end
(6.99
GHz).
The
ASS
YO
driver
voltage-to-current
converter
and
the
A47
sense
resistor
assembly
are
part
of
the
same
circuit.
This
circuit
converts
the
(scaled)
sum
of
the
PRETUNE
and
YO TUNE
voltages
to
the
YO
MAIN COIL DRIVE
current
that
drives
the
YO
main coil.
This
completes
the
YO
loop,
which
tunes
and
phase-locks
the
YO.
Sweep
Generator
Detailed
Theory
Of
Operation
The
following
assemblies
cause
the
frequency
of
the
instrument
to
sweep:
•
ASS
sweep generator
•
AS4
YO
pretune/delay
compensation
assembly
•
ASS
YO
driver.
When
the
YO
loop
phase-locks
at
the start
frequency
of
an
instrument
sweep or
at
the
start of
a
new
band,
the
AS4
YO
pretune/delay
compensation
assembly provides
PRETUNE
voltage
to
the
ASS
YO
driver.
PRETUNE
is
a
DC
voltage proportional
to the
frequency
at
which
the
YO
is
locking. The
sensitivity
of
this
voltage
is
—2.S
volts/GHz
(YO
frequency).
The
ASS
YO
driver
converts
this
voltage
to
a
current
that
is
also proportional
to the
lock
frequency.
This
current
is
fed
to
the YO
main
coil
where
it
tunes
the
frequency
of the
YO
to
be
within
the
capture range
of the
YO
phase
lock
loop.
For
sweep
widths
>S
MHz,
the
A49
YO
loop phase detector
opens
the
YO
phase-locked
loop
by
activating
the
sample
and
hold,
thus
holding
YO
TUNE
constant
at
its
phase-locked
value.
The
ASS
sweep
generator
provides
a
voltage
ramp
which
is
summed
with
the
PRETUNE
voltage
on
the
AS4
YO
pretune/delay
compensation assembly.
The
resulting
voltage
ramp
produces
a
current
ramp
from
the
ASS
YO
driver
assembly
that
in
turn
sweeps
the
frequency
of the
YO.
VSWP
is
also
used
on
the
AS4
YO
pretune/delay
compensation assembly
to
produce another
nega¬
tive
going
ramp
called
VCOMP,
This
is
added to
PRETUNE
on
the
ASS
YO
driver
assembly
to
compen¬
sate
for
the
eddy-current
induced
swept frequency
error
inherent
in
the
YO
magnetic
structure.
HP
8340B/41B
Sweep
Generator
-
YO
Loop
Theory
of
Operation
D-7

HP 8340b Specifications

General

Brand	HP
Model	8340b
Category	Inverter
Language	English