HP 492A Operating And Service Manual

Download Operating and service manual of HP 492A Amplifier for Free or View it Online on All-Guides.com.

Brand: HP

Category: Amplifier

Type: Operating and service manual

Model: HP 492A , HP 494A

Pages: 44

Download HP 492A Operating and service manual

HP 492A Operating and service manual - Page 1
1
HP 492A Operating and service manual - Page 2
2
HP 492A Operating and service manual - Page 3
3
HP 492A Operating and service manual - Page 4
4
HP 492A Operating and service manual - Page 5
5
HP 492A Operating and service manual - Page 6
6
HP 492A Operating and service manual - Page 7
7
HP 492A Operating and service manual - Page 8
8
HP 492A Operating and service manual - Page 9
9
HP 492A Operating and service manual - Page 10
10
HP 492A Operating and service manual - Page 11
11
HP 492A Operating and service manual - Page 12
12
HP 492A Operating and service manual - Page 13
13
HP 492A Operating and service manual - Page 14
14
HP 492A Operating and service manual - Page 15
15
HP 492A Operating and service manual - Page 16
16
HP 492A Operating and service manual - Page 17
17
HP 492A Operating and service manual - Page 18
18
HP 492A Operating and service manual - Page 19
19
HP 492A Operating and service manual - Page 20
20
HP 492A Operating and service manual - Page 21
21
HP 492A Operating and service manual - Page 22
22
HP 492A Operating and service manual - Page 23
23
HP 492A Operating and service manual - Page 24
24
HP 492A Operating and service manual - Page 25
25
HP 492A Operating and service manual - Page 26
26
HP 492A Operating and service manual - Page 27
27
HP 492A Operating and service manual - Page 28
28
HP 492A Operating and service manual - Page 29
29
HP 492A Operating and service manual - Page 30
30
HP 492A Operating and service manual - Page 31
31
HP 492A Operating and service manual - Page 32
32
HP 492A Operating and service manual - Page 33
33
HP 492A Operating and service manual - Page 34
34
HP 492A Operating and service manual - Page 35
35
HP 492A Operating and service manual - Page 36
36
HP 492A Operating and service manual - Page 37
37
HP 492A Operating and service manual - Page 38
38
HP 492A Operating and service manual - Page 39
39
HP 492A Operating and service manual - Page 40
40
HP 492A Operating and service manual - Page 41
41
HP 492A Operating and service manual - Page 42
42
HP 492A Operating and service manual - Page 43
43
HP 492A Operating and service manual - Page 44
44
Section
III
Paragraphs
3-23
to
3-30
output.
The
linear
modulation
region
extends
from
approximately
+4
volts
(where
beam
de-focusing
occurs)
to
approximately
-15
volts
(where
the
rf
out-
put
becomes
an
exponential
function of the
grid
volt-
age).
This
linear
operating
region
permits
up
to
30%
modulation
with
less
than 2.5%
envelope
distortion
and up
to
50%
modulation
with
less
than
5%
distortion.
Envelope
distortion
increases
rapidly
above
50%
modu-
lation.
In
pulse
work
the
twt
may
be
biased
near
or
below
cut-off
and
the
rf
drive
adjusted
for
saturation
output
at
the
peak
amplitude
of
the
modulating
pulse.
However,
the
grid
voltage
at
the
peak
of
the
modu-
lating
signal
must
not
cause
de-focusing
(approxi-
mately
+4
to
+ 8
volts)
nor
excessive
average
electrode
current,
see
table
3-1.
The
transient
response
of
the
492A
or
494A to a
step
function
applied
to
the
grid
is
approximately
15
nsec.
3-23.
Amplitude
modulation
is
accompanied
by
some
incidental
phase
modul'btion of
the
rf
signal,
amount-
ing
to
approximately
90
phase
shift
of
the
rf
carrier
for
a 10 db
change
in
the
modulated
rf
output
level.
In
practice
this
phase
modulation
is
unimportant
when
using
the
conventional
square-law
crystal
detectors,
but
is
important
in
detection
systems
where
the
out-
put
is
a function
of
the
rf
carrier
phase.
3-24.
PULSE
MODULATION.
3-25.
There
is
considerably
latitude
in
the
adjustment
of
modulation
characteristics
when
pulse
modulating
an
rf
signal
using
the
492A
or
the
494A;
see
figures
3-5
and
3-6.
The
cw
input
level,
the
modulation-
pulse
amplitude,
and
the
grid
bias
determine
the
characteristics
of
the
rf
output
pulse
as
follows:
a.
The
cw
input
signal
primarily
determines
the
maximum
possible
level
of
the
rf
output
pulse
and
whether
or
not
the
twt
can
be
operated
into
saturation.
b.
The
peak-to-peak
amplitude
of
the
modulating
pulse
primarily
determines
the
on-off
ratio
of
the
rf
output
pulse.
c.
The
grid
bias
level
primarily
determines
the
rf
output
levels
attained
during
the
pulse-on
and
pulse-
off
times
and
also,
in
conjunction
with
the
modulating
pulse,
determines
the
rf
input
level
necessary
to
saturate
the
twt.
The
GRID BIAS
control
always
should
be
set
so
that
the
twt
grid
will not
draw
cur-
rent
(approximately
4
volts
positive)
during
the
pulse-
on
period.
3-26.
To
pulse
modulate
the
rf
signal
being
amplified
in
the
492A
or
494A,
refer
to
figures
3-5
or
3-6
and
proceed
as
follows:
a.
Determine
if
the
twt
is
to be
driven
into
satura-
tion
and
if
the
rf
output
must
be
at
a
specific
level.
b.
Set
the
GRID BIAS
control
for
zero
bias.
c.
Connect
the
rf
input
signal
to
the
twt and
adjust
its
level
to
produce
the
desired
rf
pulse
output
level.
d.
Determine
the
on-off
voltage
ratio
required
in
the
rf
output
pulse.
3-6
Model 492A/494A
e.
Using
the
graph
in
figure
3-5
determine
the
magnitude
of
modulation
pulse
required
to
produce
the
desired
on-off
ratio.
f.
Set
the
GRID BIAS
control
to
obtain
the
voltage
determined
in
step
e.,
Le.,
the
peak
voltage
of
the
modulating
pulse.
The
bias
VOltage
may
be
measured
at
the
pin
jack
on
the
front
panel.
g.
Connect
the
modulating
pulse
to
the
GRID MOD.
connector
and
adjust
its
amplitude
to
the
voltage
de-
termined
in
step
e to
produce
the
desired
on-off
ratio
in
the
rf
output
pulse.
Since
the
grid
of
the
twt
is
con-
nected
directly
to
the
GRID MOD.
jack,
a
dc
com-
ponent
in
the
modulating
signal
will
affect
the
grid
bias.
Also,
if
capacitive
coupling
is
used
the
modu-
lating
signal
will
drive
the
grid
of
the
twt
above
and
below
the
dc
level
established
by
the
grid
bias,
an
amount
determined
by
the
duty
cycle
of
the
modulating
signal.
The
GRID BIAS
control
must
be
adjusted
to
compensate
for
both of
these
effects.
h.
To
increase
the
on-off
ratio
of
the
rf
output
pulse,
increase
the
amplitude
of
the
modulation
pulse,
at
the
same
time
adjust
the
grid
bias
so
that
the
grid
will not be
driven
beyond 4
volts
positive,
see
the
Note
paragraph
3-21.
Note
Large
input
modulating
pulses,
above
15
volts,
tend
to
shock-excite
the
helix,
produc-
ing
ringing
on
the
top of
the
rf
output
pulse
and a slow
rise
time.
If
the
traveling-wave
tube
is
operated
near
saturation
this
effect
is
minimized
and
better
pulse
characteristics
are
obtained.
3-27.
LIMITED
PHASE
MODULATION.
3-28.
The
signal
being
amplified
in
the
492A
or
494A
can
be
phase-modulated
by applying
voltage
to
the
HELIX MOD.
connector.
This
voltage
varies
the
electron-beam
velocity
by
changing
the
potential
be-
tween
the
cathode
and
the
helix--a
positive
voltage
change
accelerates
the
electron
bunches
and
advances
the
phase
of
the
rf
output
signal;
a
negative
change
slows
them
and
retards
the
phase
of
the
output
signal.
The
resultant
phase
deviation
in
the
output
signal
is
directly
proportional
to
the
applied
voltage.
The
de-
gree
of
phase
deviation
produced
is
limited
by
the
range
of
helix
voltages
that
produces
amplification,
and
by
the
amount
of
incidental
amplitude
modulation
permissible
in
the
rf
output.
Phase
deviation
of 360
0
is
possible
with
the
output
amplitude
held
to
variations
of
approximately
1-1/2
db and
is
obtained
with a
helix
voltage
variation
of
less
than 50
volts.
The
actual
voltage
required
for
a
phase
shift
of
360
0
varies
with
the
operating
frequency
and
from
tube-to-tube.
3-29.
UNLIMITED
PHASE
MODULATION
AND
FREQUENCY
SHIFTING.
3-30.
Although
the
limited
phase
deviation
described
in
paragraph
3-27
is
useful
in
some
applications,
un-
limited
phase
deviation
has
a
much
wider
range
of
usage.
It
is
particularly
useful
because
the
frequency
00144-2