HP 8508A - Operation

Operation
5.
Now
increase
the
source
frequency
until
the
display
reads
-3dB.
Note
the
source
frequency.
This
is
the
filter
3dB
cutoff
frequency.
:
a. Transmission
One
good
use
of
a
CW
receiver
such
as
the
HP
8508A
is
in
the
measurement
of
gain
as
a
function
of
input
level.
The
HP
8508A
automatically
displays
B/A
as
a
ratio,
so
effects
caused
by
changing
input
level
can
be
seen
directly.
To
illustrate
this
we’ll
measure
the
1dB
gain
compression
point
of
a
S0MHz,
14dB
gain
amplifier.
Since
the
output
at
gain
compression
is
specified
to
be
10dBm,
we’ll
use
an
HP
8491A
10dB
attenuator
at
the
output
of
the
amplifier
to
minimize
measurement
errors
due
to
high
signal
levels.
Source
HP8S508A
50 ohm 50 ohm
- "A" Input "B* Input
Power
Splitter
Device Under Test
Figure 3-11. Transmission Test Setup
1,
Connect
the
A
and
B
inputs
to
the
power
splitter.
Set
the
source
output
level
in
the
normal
operating
range
of
the
"
amplifier.
Set the
source
output
frequency
to
5S0MHz.
Press
[PRESET]
to
return
the
HP
8508A
to
a
known
state.
2.
Press
[B/A
MAG]
to
measure
the
magnitude
ratio.
Select
[DISPLAY]
dB
to
measure
log
gain.
Press
[SHIFT]
then
[SAVE
REF}
to
store
the
current
measurement,
zero
the
display
and
remove
splitter
and
input
effects.
—
3.
Connect
the
amplifier
between
the
splitter
and
the
B
input
and
measure
and
note
the
gain.
4,
Press
[SHIFT]
then
[SAVE
REF]
to
store
and
use
this
(nominal)
gain
as
a
reference
and
reset
the
reading
to
OdB.
5.
Increase
the
source
output
level
until
the
HP
8508A
reads
1dB.
The
amplifier
is
now
operating
at
its
gain
com-
pression
point.
6.
Press
[REF]
to
remove
the
reference
offset.
Press
[A
MAG]
to
measure
the
input
voltage
(dBuV),
and
[POWER
MEAS]
to
convert
the
reading
to
dBm.
Since
the
splitter
is
symmetrical,
the
measured
power
at
the
A
input
will
be
the
same
as
at
the
amplifier
input
to
within
the
tracking
specifications
of
the
power
splitter.
3-16
Q@uunnunnnnnuununQ@aus
.
ae @easen