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HP 8340b Operating Instructions

HP 8340b
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Pulse
Envelope
The
pulse
envelope
produced
by
the
HP
8340B/41B
is
not
a
perfect
rectangle,
rather
it
has
finite
rise
time,
overshoot,
and
video
feedthrough.
Below
2.3
GHz
the
rise
time
and
overshoot
are
essentially
independent
of
frequency,
but
above
2.3
GHz
they
are
strongly
influenced
by
the
passband
shape
and
centering
of
the
HP
8340B/41B’s
tracking
YIG
filter.
Best
envelopes
are
normally
obtained
by
using
the
PEAK
function.
The
envelopes
will
change
with
frequency
and
slightly
with
power
level.
Source
Match
In
the
absence
of
attenuation
with
a
resistive
pad,
a
leveled
microwave
source
generally
provides
a
50ft
source
match
at
its
operating
frequency
only.
The
source
match
at
other
frequencies
is
that
of
the
unleveled
RF
hardware.
In
this
case
this
is
a
YIG
filter
which
is
a
good
reflection
for
anything
more
than
about
20
MHz
off
center,
and
not
much
better
within
its
passband.
The
match
is
good
only
for
signals
at
the
output
frequency
plus
or
minus
the
leveling
loop
bandwidth.
Thus
a
CW
reflection
will
be
absorbed.
A
time
varying
reflection,
as
from
a
reflective
modulator,
may
contain
modulation
side¬
bands
outside
the
leveling
loop
bandwidth.
If
so,
these
sidebands
may
be
re-reflected.
When
pulse
modulating,
any
reflection
of
the
pulse
will
contain
sidebands
far
outside
the
loop
bandwidth,
so
the
leading
edge
of
the
reflection
will
be
re-reflected.
In
this
manner
a
poorly
matched
system
can
gener¬
ate
very
poor
envelopes
(anywhere
in
the
system,
not
only
at
the
source).
Performance
is
improved
by
padding
between
the
reflections.
At
the
source,
if
output
powers
above
-10
dBm
are
in
use,
coupled
mode
results
on
0
dB
RF
attenuation.
If
enough
power
is
available,
decoupled
mode
may
be
used
to
improve
the
HP
8340B/41B’s
source
match
by
inserting
10
dB
attenuation
and
using
a
10
dB
high
ALC
level.
Video
Feedthrough
Video
feedthrough
is
a
low
frequency
signal,
at
the
modulation
rate,
which
is
superimposed
on
the
RF
envelope.
See
Figure
3-37.
If
large
enough,
video
feedthrough
can
disturb
mixer
balance,
amplifier
bias,
crystal
detector
output,
etc.
Since
it
is
low
frequency
energy,
it
can
distrub
systems
which
are
not
intended
to
deal
with
it,
especially
demodulation
systems.
HP
8340B/41B
Operating
Information
3-115

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HP 8340b Specifications

General IconGeneral
BrandHP
Model8340b
CategoryInverter
LanguageEnglish

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