Trouble Shooting Guide, Advanced
4/00021-3/FEA 209 544/25 C
Ericsson Mobile Communications AB
22(78)
7.2.3
The RX level is too high
When the RX level is too high (some steps above the limit) it is often due to some component
in the signal path that has changed characteristic because of ageing.
The only thing you have to do is a new RSSI-calibration.
7.2.4
The RX level is too low
When the RX level is too low (some steps under the limit) and the RX quality is 0, it is often
due to some component in the signal path that has changed characteristic because of ageing.
It is advisable to do a new RSSI-calibration.
If there is a RX quality problem and the fault remains after RSSI-calibration or if there is a
big RX level- fault (RX quality-fault), go to section 7.2.5.
7.2.5
RX QUALITY- fault
The base-station sends out a pattern of bits that the phone loops back to the base-station.
The base-station then compares the original pattern with the one the phone sent back and
calculates a percentage on the difference.
This percentage is used to measure the RX QUALITY.
This calculation is performed during a call, for EGSM900 at –102 dBm RX-signal and power
level 5 at low, middle and high channel (978, 37 and 124). For GSM1800 at –100 dBm RX-
signal and power level 0 at low, middle and high channel (512, 699 and 885).
RX QUALITY should be 0-2 steps.
If it is higher on any of the channels then it is almost always receiving problem
7.2.6
How do you find the fault
By generating a signal with a GSM-test instrument and measure the signal path on the board
with a spectrum analyser and compare the signal strength with earlier measured values (i.e.
compare against a reference-board).
The signal path is partly different for EGSM900 and GSM1800.
7.2.7
For EGSM900
Set Radio in RX Static mode on channel 37, Fig. 7.1.
Static RX activates when you have clicked on the Apply-button.