User Manual

Appendix B: Monitor and Test Links
76 Version 1.1 - 01/04/00
Monitoring Null Depth
The Null Depth is the ratio in dB between the strongest OFDM carrier and the weakest
carrier. A Null Depth of greater than 0 dB indicates that there is no multipath reception.
Some multipath is usually present in your link, however adjustments to the position or
location of the receive antenna at the remote site can minimize the Null Depth. In some
cases, you cannot adjust the antenna position and location of the receive antenna at a
remote site.
Monitoring Fade Margin
The Fade Margin is the receive power in excess of the minimum required for error free
operation. See Monitoring RSSI on page 75 for information about receive power.
Fade Margin is computed for you using the following formula:
Thus, we have verified that the correct Fade Margin of 13dB is displayed.
Note:
Check the back of the 300-24 unit for a label identifying that a Fade Margin
Correction Factor has been applied to the unit. If so, apply the following correction factor:
Actual Fade_Margin = Fade_Margin - Fade_Margin_Correction_Factor
Performing a Link Test
Linktest is a diagnostic tool for setting up and diagnosing links. Typically, you use linktest
when you:
• initially set up a remote
• diagnose a problem link
Linktest generates pseudo-random packets of information that are transmitted to the
station ID provided. The unit, or station ID, compares the pseudo-random data and
accumulates bit errors, RSSI, Fade Margin, and Forward Error Correction (FEC) statistics.
These statistics and regenerated pseudo-random data are sent in a packet back to the
originating unit. The originating unit then compares the pseudo-random data and at
approximately one second intervals, displays the accumulated statistics in the
configuration menus.
Before you start a linktest, you need the station ID of the base station. See Setting the RF
IDs and Center Frequency on page 58 for information about viewing station ID settings.
Formula Fade Margin = RSSI - Null Depth - Receiver Sensitivity
Example
Variables
RSSI = -62dBm
Null Depth = 3dB
Receiver Sensitivity = -78dBm
Fade Margin = 13dB
Calculation Fade Margin = -62dBm - 3dB - -78dBm
Fade Margin = 13dB