HP 8510 User Manual

Changing Signal Path After Calibration
If any attenuator or other external equipmentischanged after calibration, the measurement
results cannot b e specied except byyour own estimation of the error contribution of
the change. For example, when the p ort attenuation is changed with correction On, the
CAUTION: CORRECTION MAY BE INVALID is displayed. The op erator must judge
whether the error is tolerable in the particular application and how to comp ensate for the
change.
The only reason to change the internal attenuators or external equipmentbetween calibration
and measurement is to maximize the levels under b oth conditions, thus minimizing
uncertainty due to noise. Many factors will enter into the decision of whether it is more
accurate to calibrate at a low signal level without changing the setup, or change the setup
to optimize levels for both calibration and measurement. Changing the Port 1 or the
Port 2 attenuator do es not seriously change the test set mismatc h, directivity, or isolation
characteristics, but will change the frequency resp onse magnitude and phase. This dierence
in the frequency resp onse between calibration and measurement can be normalized using the
HP 8510 trace memories.
The
application
question
is:
Do
es
increasing
the
signal
lev
els
during
calibration
impro
v
e
the
calibration enough
to
risk
greater
error
con
tributions
p
ossible
b
y
c
hanging
the
setup?
Set
the
A
ttenuators
If
only
the
P
ort
1
or
P
ort
2
attenuators
are
c
hanged,
the
follo
wing
pro
cedure
can
minimize
the
errors.
1.
Connect
a
short
or a
thru
and
set
the
P
ort
1
and
P
ort
2
atten
uators
for
b
est
IF
signal
lev
els
during
calibration.
2.
P
erform
the
appropriate
measuremen
t
calibration.
3.
With
an
appropriate
standard
connected,
set
the
Port
1and
P
ort
2
atten
uators
to
the
setting
required for
operating
the test
device.
If
y
ou
view the
response
of a
short
circuit,
notice
that
c
hanging
the
P
ort
1
atten
uators
has negligible eect on the S
11
marker reading, and that changing Port 2 attenuators has
negligible eect on the S
22
marker reading. This is due to the way that the attenuators are
paired. Both the reference and the test signal are changed an approximately equal amount.
However, when viewing S
21
or S
12
,changing the Port 1 or Port 2 attenuators osets the
mark
er
reading
b
y
the
dierence
in
the
P
ort
1and
P
ort
2
v
alues.
Store Trace Memories
The main frequency resp onse eects of c
hanging the atten
uators can b e comp ensated for b
y
using the HP 8510 trace memories and trace mathematics as follo
ws.
1. Connect the thru used for calibration. Set the port atten
uators to the v
alue used for
measurement of the device. Recheck the user parameter levels then press 4
S
21
5 .
2.
Press
4
DISPLA
Y
5
NNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNN
DATA
!
MEMORY
to
store
the
S
21
trace
in
default
trace
memory
1.
This
trace
is
the
frequency
resp
onse
dierence
of
the
S
21
signal
path
b
et
w
een
calibration
and
measuremen
t.
10-6
High
P
o
w
er
Measurements

HP 8510 Specifications

General

Brand	HP
Model	8510
Category	Measuring Instruments
Language	English