User Guide: Technical
Reference SECTION 5 TROUBLESHOOTING ALARM CONDITIONS FOR
ioLink 4
PRELIMINARY
Customer Support (202) 333-7031
5-2
5.4 FEC BER > x.x E-x
Pre-FEC BER has exceeded the BER Threshold for the BER Interval
1. Check that the RF Signal Level is acceptable (>83%). If it is below 83%, go to the section on
troubleshooting the Low RF Power alarm.
2. Check that the BB Signal Level is acceptable (>40%). If it is below 40%, go to the section on
troubleshooting the RX Low Symbol Power Alarm.
3. Check the Pre-FEC BER in the STATUS menu:
a. If it has dropped back below the BER Threshold, note the time of day that the alarm occurred.
This may allow you to track down the source of the fade if this alarm periodically appears.
Some possible sources of fading could be noise, interfering signals, temporary obstructions
(such as someone standing directly in front of the antenna) or the operation of a microwave
oven in the vicinity.
b. If the Pre-FEC BER continues to remain above the BER Threshold, check the link for possible
obstructions or interference. Obstructions could be anything from new buildings or walls to
growing trees or changes in the landscape. For example, if a stand of trees between the two
antennas grows enough to sufficiently block the Fresnel zone, the Pre-FEC BER will increase.
Also, if that same stand of trees is removed, there could be multi-path fading effects causing
a problem. To check for sources of interference, look for other similar systems in the area or
use a spectrum analyzer to detect the noise floor and any other signals in the vicinity of the
antennas that are in or near the ISM band. Note the frequency, power and direction of the
interfering signal. This will help in adjusting the antenna direction or polarization to reduce the
interference.
5.5 FEC Decoder Not Locked
FEC circuitry has discovered an error in the bit stream
1. Restart the near end Modem unit. Since the cause of this alarm is that the FEC detects a data
bit set that is not one of the valid possibilities it is looking for, it is most likely that the circuitry is
out of sync. This means it is looking at the end of one set and the beginning of the next set
instead of looking at each individual set completely. Usually the spreading section will fix this
problem automatically, but if it doesn’t, this alarm condition will appear. Restarting the near end
Modem unit attempts to bring the FEC back into sync with the other side.
