Specifications

160 Chapter 15
Concepts
Stimulus Response Measurement Concepts
Concepts
Reconnect the DUT to the analyzer. Note that the units of the reference
level have changed to dB, indicating that this is now a relative
measurement. Change the normalized reference position:
Press
View/Trace, More, Normalize, Norm Ref Posn.
Arrowheads at the left and right edges of the graticule mark the
normalized reference position, or the position where 0 dB insertion loss
(transmission measurements) or 0 dB return loss (reflection
measurements) will normally reside. You can change the position of the
normalized trace, within the range of the graticule by entering a
position number.
Measuring Device Bandwidth
It is often necessary to measure device bandwidth, such as when testing
a bandpass filter. There is a key in the
Peak Search menu that will
perform this function. The device signal being measured must be
displayed before activating the measurement. The span must include
the full response.
Activate the measurement by toggling the
N dB Points key to On. The
analyzer places arrow markers at the
−3 dB points on either side of the
response and reads the bandwidth. For other bandwidth responses
enter the number of dB down desired, from
−1 dB to −80 dB.
No other signal can appear on the display within N dB of the highest
signal. The measured signal cannot have more than one peak that is
greater than or equal to N dB. A signal must have a peak greater than
the currently defined peak excursion to be identified. The default value
for the peak excursion is 6 dB.
Measurements are made continuously, updating at the end of each
sweep. This allows you to make adjustments and see changes as they
happen. The single sweep mode can also be used, providing time to
study or record the data.
The N dB bandwidth measurement error is typically
±1% of the span.
Converting Return Loss to VSWR
Return loss can be expressed as a voltage standing wave ratio (VSWR)
value using the following table or formula:
Table 15-6 Power to VSWR Conversion
Return
Loss
(dB)
VSWR Return
Loss
(dB)
VSWR Return
Loss
(dB)
VSWR Return
Loss
(dB)
VSWR Return
Loss
(dB)
VSWR
4.0 4.42 14.0 1.50 18.0 1.29 28.0 1.08 38.0 1.03
6.0 3.01 14.2 1.48 18.5 1.27 28.5 1.08 38.5 1.02