User Manual

August 6, 2003 Part 004071A revision 00b 111
Chapter 4: Installation Procedures
Measuring VSWR and Return Loss
Voltage standing wave ratio (VSWR) is a ratio of the maximum to minimum
voltage as measured along the length of a mismatched RF transmission line.
VSWR indicates the level of impedance matching between RF equipment (such
as amplifiers, cabling, and antennas). When the impedances of the RF equipment
are mismatched, some of the RF energy is reflected back along the transmission
line. Reflected energy causes inefficiencies in the transmission power output.
A VSWR of 1:1, as measured from antenna cable to the antenna, indicates that
100% of the power output is being radiated by the antenna. During a cable
sweep, Amosphere RF equipment should show a VSWR of 1.5:1 or less, as
measured from 1850–1990 MHz. A VSWR greater than 1.5:1 indicates potential
problems with the RF equipment.
A high VSWR may be caused by one or more of the following conditions:
 Moisture in the external cables or connectors
 Faulty equipment
 Poor connections between components
 Damaged cables or connectors
 An open- or short-circuit in RF equipment or cables
Return Loss
Return loss is closely related to VSWR. Return loss is a measure in decibels (dB)
of the ratio of forward to reflected power. For example, if a load has a return loss
of 10 dB, then 1/10 of the forward power is reflected. The higher the return loss,
the less energy is being reflected.
installation.book Page 111 Wednesday, August 6, 2003 6:06 PM