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19 Sensitivity (RX-quality)
19.1 What is RX-quality
The base-station sends out a pattern of data-bits, which 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 GSM 900 at -102 dBm RX-signal and power level 5 at low, middle and high channel (1, 62
and 124).
For GSM 1800 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 s receiving problem.
19.2 How to 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 GSM 900 and GSM 1800:
For GSM 900 go to section 19.3.
For GSM 1800 go to section 19.4.
19.3 GSM 900
Open the phone and check for liquid damages.
No further action should be taken for a liquid damaged telephone.
Attach the board to the fixture and start the test program.
Set Radio in RX Static mode on channel 62 Fig. 19.1
Static RX activates when you have clicked on the Apply-button.
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Trouble Shooting Guide, Advanced
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