Anritsu 37 C Series, Operation Manual

Page: 226 / 603

(TDR) you may feel more comfortable with step response, as the dis-
plays are similar.
The lowpass step response for a resistive impedance is a positive level
shift for R>Z
0
and a negative level shift for R<Z
0
. The height of the re-
sponse is equal to the reflection coefficient
r = -
+
R Z
R Z
0
0
The step response for a shunt capacitance is a negative peak, and for a
series inductance it is a positive peak (Figure 9-3).
An example of using the lowpass step response is cable-fault location.
In the frequency domain a cable with a fault exhibits a much worse
match than a good cable. Using lowpass step response, both the loca-
tion of the discontinuity and the information about its type are avail-
able (Figure 9-4).
In the above example, the dip in the display shows the shunt-
capacitive response caused by a crimp in the cable. The response at
the end of the cable shows the step-up that is typical of an open (Fig-
ure 9-3, left).
The 37XXXC bandpass mode gives the response of the DUT to an
RF-burst stimulus. Two types of response are available: impulse and
phasor-impulse. An advantage of the bandpass mode is that any fre-
quency range can be used. Use this mode with devices that do not have
a dc or low-frequency path.
37XXXC OM 9-5
TIME DOMAIN TIME DOMAIN MEASUREMENTS
LOWPASS IMPULSE RESPONSE
Location of Discontinuities
Information on Type of Discontinui-
ties
C I R C U I T E L E M E N T S
R > Z
O
S H U N T C
S E R I E S L
I M P E D A N C E
O
R < Z
1 1
S R E A L
L o w p a s s S t e p R e s p o n s e
Figure 9-3. Lowpass Step Re-
sponse
4 0 . 0 0 0 c m
0 . 0 0 0 m m
1
3
C A B L E
2
O P E N
Figure 9-4. Example of Lowpass Step Response
LOWPASS STEP RESPONSE
TDR Measurement
Location of Discontinuities
Information on Type of Discontinui-
ties