User's Manual

Tune Up procedures for Q2426.
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This paper aims to explain the function of each radio parameters which are in the eeprom, the way to
calculate each of them and the way to load them in the eeprom.
- ThinDacValue : (former THIN_DAC_INIT_VALUE in the file EEPROM.H). The value
given to this parameter is loaded in the 10 bits AFC DAC when the mobile is powered on.
For more explanation about this parameter, have a look to the description of the parameter
RoughDacValue below.
The global excursion of the thin DAC is about 30 ppm, so the slope is about - 0.03 ppm for one step. It
means that when the value loaded in the thin DAC is increased by one, the frequency of the VCXO
decrease by 0.03 ppm.
The thin DAC is used by the software to controle the frequency of the VCXO when the mobile is
synchronised on the network to compensate doppler and temperature drift.
- RoughDacValue : (former CARTE_DAC_INIT_VALUE in the file EEPROM.H). The value
given to this parameter is loaded in the 8 bits DAC (GTI radio) 3 bits DAC (GISMO radio) when the
mobile is powered on.
This value should be such that the VCXO accuracy is better than 0.1 ppm at a temperature of 20 ° C
when both ThinDacValue and RoughDacValue are loaded.
The global excursion of the Rough DAC is about 80 ppm, so the slope is about + 0.3 ppm by step for
GTI radio and + 10 ppm by step for GISMO radio. It means that when the value loaded in the rough
DAC is increased by one the frequency of the VCXO increase by 0.3 ppm (GTI radio) 10 ppm
(GISMO radio).
The rough DAC is used by the software to compensate aging drift of VCXO.
A good way to calculate the value to give to the parameters ThinDacValue and RoughDacValue, is to
measure by any mean the frequency of the VCXO while the value loaded in the two DAC are half the
excursion (512 for the thin DAC, 128 for the rough DAC for GTI radio, 4 for the rough DAC for
GISMO radio).
Then, calculate first the best value to give to RoughDacValue and then the best value to give to the
ThinDacValue.
As the slope of the rough DAC and of the thin DAC may vary around the value given, the whole
process should be lead again one or two time.
e.g : the measure of the VCXO give 13.0002 MHz
∆f/f = 200/13 E6 = +15.4 ppm
For WISMO radio : The value loaded in the rough DAC should be decreased by (15.4 + 5) / 10
= 2
So RoughDacValue = 4 - 2 = 2.
Then there is (15.4 - 10 x 2) = - 4.6 ppm left to be compensated with the
thin DAC.
To do so, the value loaded in the thin DAC should be decreased by 4.6 /
0.03 = 153.
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