Keysight Technologies N9330B, User Manual

Page: 35 / 107

Making Measurements
Measuring Return Loss/SWR/Cable Loss
29
Measuring Return Loss/SWR/Cable Loss
Return loss is the measurement of the signal reflection
characteristics of a cable and antenna system. A return
loss measurement is useful in detecting problems in the
antenna feedline system and the antenna itself. A
portion of the incident power is reflected back to the
source from transmission line faults as well as from the
antenna itself. The ratio of the reflected voltage to the
incident voltage is called the reflection coefficient. The
reflection coefficient is a complex number, meaning it
has both magnitude and phase information. In
S-parameter terms, return loss is referred to as an S11
measurement.
SWR and cable loss measurement derive from return
loss measurement.
Perform a basic return loss measurement
When measuring return loss, SWR, or cable loss with
your N9330B, follow the same operation procedure as
shown below.
To make a return loss (versus. frequency) measurement
over a frequency range of 50 to 400 MHz, perform the
following steps:
1 Press the
[MODE]
hardkey to call up a measurement
mode menu. Rotate the front-panel knob to select a
measurement mode (for this example, Return Loss).
Press the
[ENTER]
hardkey to confirm your selection.
For more detailed information, refer to "Selecting a
Measurement Mode" on page 24 .
2 Press the
{Start}
softkey to call up the start frequency
menu. Press
{50} > [ENTER]
to set the start frequency
to 50 MHz.
NOTE
Test signals can cause interference. When testing cables attached
to an antenna, the test signal is radiated from the antenna. Verify
that the signal used for the test CANNOT cause interference to
other antennas.