Nokia RH-6 Series Rf Description & Troubleshooting page 36

RH-6
7 - RF Description & Troubleshooting
The VCXO calibration finds out a calibration value for VCXO control, an AFC initial value
and 3 AFC-slope coefficients. The VCXO calibration ensures the function of an initial syn-
chronization (before location update is done) when the phone is in Normal mode. For an
error free initial synchronization, the 26MHz frequency of the VCXO must be accurate
enough. Therefore, a VCXO cal value is written into the RefOSCCAL register of the
Mjoelner.
During VCXO-calibration, the VCXO cal value is changed by a DSP-algorithm until a syn-
chronization is possible. This means the VCXO oscillates at 26 MHz with a sufficient min-
imum frequency error.
To further minimize the frequency error, an initial AFC value is determined by the DSP
and written into RefOSCAFC register of the Mjoelner.
Additionally the DSP algorithm determines three AFC slope coefficients Slope C1...3
during VCXO calibration. One AFC slope value is not sufficient for Mjoelner, because the
AFC slope is non-linear in this chip.
The AGC-calibration finds the gain values of the RX chain. The AGC consists of RF LNA,
which can be either on or off (gain difference between on and off state is nominally
30dB) and BB gain which can be controlled in 6dB steps. This gives 15 gain steps RSSI0
to RSSI14. LNA is off for steps RSSI0 to RSSI4.
AGC-calibration measures the gain at gain step RSSI4 and RSSI7. The other gain values
are calculated.
A value RF_TEMP, which represents the RF hardware temperature, is determined during
RX Calibration. This temperature value is used by DSP for RSSI reporting correction in
Normal mode of the phone. It is not visible in the calibration process.
The RX calibration is only valid if the results are within certain limits. For the most recent
limits see the production limits of FLALI and FINUI testers.
If the results are not within these limits, there is a fault in the RX chain.
RX calibration EGSM900
Set operating mode to local mode.
Select
Wait until the RX Calibration window pops up.
Select
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Maintenance
Tuning
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Copyright © 2003 Nokia Corporation.
Company Confidential
CCS Technical Documentation
RX Calibration
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GSM 900
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Issue 1 10/2003