User Guide

PMP 450 Planning Guide
Calculating Fade Margin
Free space path loss is a major determinant in Rx (received) signal level. Rx signal level, in turn, is a major
factor in the system operating margin (fade margin), which is calculated as follows:
system operating margin (fade margin) dB =Rx signal level dB − Rx sensitivity dB
Thus, fade margin is the difference between strength of the received signal and the strength that the receiver
requires for maintaining a reliable link. A higher fade margin is characteristic of a more reliable link.
Analyzing the RF Environment
An essential element in RF network planning is the analysis of spectrum usage and the strength of the signals
that occupy the spectrum you are planning to use. Regardless of how you measure and log or chart the results
you find (through the Spectrum Analyzer in SM feature or by using a spectrum analyzer), you should do so:
• at various times of day.
• on various days of the week.
• periodically into the future.
As new RF neighbors move in or consumer devices in your spectrum proliferate, this will keep you aware of the
dynamic possibilities for interference with your network.
Mapping RF Neighbor Frequencies
These modules allow you to
• use an SM or an AP that is temporarily transformed into an SM, as a spectrum analyzer.
• view a graphical display that shows power level in RSSI and dBm at 5-MHz increments throughout the
frequency band range, regardless of limited selections in the Custom Radio Frequency Scan Selection List
parameter of the SM.
• select an AP channel that minimizes interference from other RF equipment.
The following procedure causes the SM to drop any active RF link. If a link is dropped when the spectrum analysis begins,
the link can be re-established when either a 15-minute interval has elapsed or the spectrum analyzer feature is disabled.
pmp-0047 (March 2014)
1-95