Anritsu S251B - Manual (Page 47)

Chapter 4
Measurements
Introduction
This chapter provides a description of the Site Master measurement functions and examples
of frequency domain, distance domain, and two-port (insertion gain or loss) measurements.
Measurement Functions
Site Master operation is divided into four measurement modes: frequency domain, distance
domain, two-port, and power monitor.
· Frequency domain measurements consist of Return Loss (RL), Standing Wave Ratio
(SWR), and Cable Loss (CL) made over a selectable frequency range. SWR and RL char-
acterize the magnitude of reflections present in a device or transmission line. CL mea-
surements display the insertion loss of a transmission line over frequency.
· Distance domain measurements—commonly known as distance-to-fault (DTF)—are
made over a selectable distance range. They include RL or SWR, but they also return in-
formation that can help locate discontinuities in a transmission line. CL cannot be meas-
ured in the distance domain.
· Two-port transmission gain or loss measurement is commonly known as S21 or through
measurement. The gain or loss measurement is made over a selectable frequency range
and the magnitude in dB characterizes the performance of the device under test. Gain and
loss measurement includes Tower Mount Amplifier (TMA) verification, an-
tenna-to-antenna isolation, and duplexer filter rejection and isolation.
· Power monitor measurements can be either absolute or relative to some base power level,
and can be displayed in either dBm or Watts. To allow measurement and display of
power levels above the unit's specified input, the user may attenuate the signal and enter
the corresponding offset. The offset is added to the measured input power prior to dis-
play. Finally, a zero adjust function is provided to allow subtraction of an inherent
“noise” level prior to display.
CAUTION: The measurement system MUST be calibrated at the ambient tem-
perature prior to making a measurement. You must calibrate when the setup
frequency is changed. Calibrations are stored with each of the setups.
It is recommended that the appropriate calibration, (open-short-load or
open-short-load-thru) be performed on the Site Master prior to measurements. This gives
confidence to the operator that the measurement performed is accurate and system uncer-
tainties have been minimized.
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