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RM-25
RF troubleshooting
After the DtoS and BIQUAD blocks, there is another AGC-amplifier which provides a gain control range of 42 dB
in 6 dB steps. The correlation between the gain steps and the absolute received power levels is found by a
calibration routine in the production for each assembled phone.
In addition to the AGC steps, the last AGC stage also performs the real time DC offset compensation, which is
needed in a direct conversion receiver to cancel out the effect of the local oscillator leakage. DC offset
compensation is performed during an operation called DCN1. DCN1 is carried out by charging capacitors at the
input of the last AGC stages to a voltage, which causes a zero DC offset. To improve the accuracy a DC level
alignment possibility has been added to Helgo.
After the last AGC stages the single ended and filtered I- and Q-signals are fed to the RX ADCs. The maximum
peak-to-peak voltage swing for the ADCs is 1.45 V.
Measuring Rx/IQ signals using RSSI
Context
Steps
1. Start Phoenix service software.
2. Establish a connection to the phone.
From the File menu, choose "Open Product".
From the list, select RM-25.
3. From the Testing menu, choose RF Controls.
4. In the RF Controls window:
• Select Band: GSM900/GSM1800/GSM1900.
• Set Active unit to Rx.
• Set Operation mode to Burst.
• Set Rx/Tx channel in the following way: EGSM900: 37, GSM1800: 700 and GSM1900:661.
5. From the Testing menu, choose RSSI Reading.
The setup now looks like this:
6. Apply a signal frequency of:
• EGSM900: 942.4677MHz (channel 37 + 67.7KHz offset)
• GSM1800: 1842.8677MHz (channel 700 + 67.7KHz offset)
• GSM1900: 1960.0677MHz (channel 661 + 67.7 KHz)
7. In RSSI reading, click Read now.
Results
The resulting RSSI level should be -80dBm in each band.
9235618 (Issue 2)
Company Confidential
Copyright ©2005 Nokia. All Rights Reserved.
Nokia Customer Care
Page 7–9
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