Nokia 3105 Servicehandbuch

CCS Technical Documentation

Troubleshooting - RF

RH-48

Issue 1 11/2003

© 2003 Nokia Corporation         Confidential

Page 3

First check the RX AGC PDM value when troubleshooting the receiver. The AGC value 
should be close to the typical values in the tables. The Rx AGC tries to keep a constant 
amplitude at the output of the receiver chain. If the AGC value indicates an AGC gain 
that is substantially higher than normal, the AGC is compensating for extra loss in 
another component. If the AGC PDM values are normal but there is still a problem, check 
the actual AGC voltages. RF probing at specific locations in the chain can help to pin-
point the source of the problem.

Likewise, first check the measured output power and AGC values when troubleshooting 
the transmitter, which give an indication of where to start probing.

Although the tables in this chapter include power levels for many combinations of AGC 
values, it is generally only necessary to check one combination. The additional informa-
tion is provided for use in unexpected situations. Likewise, although probing points and 
signal-level information are given for each point in the receiver and transmitter chains, it 
is not necessary to probe each point on every phone — only the suspected trouble spots.

Absolute power measurements were made with an Agilent (HP) 85024A active 
high-impedance probe. Other probes may be used (make sure the probe is high-imped-
ance so the measurement does not load the circuit), but they may have different gains. 
Therefore, adjust the absolute measurements accordingly, especially if you are using a 
probe attenuator.

Typically, the higher loss occurs at the band edges where a range is given for loss. Prob-
ing is not a very accurate method to measure absolute power; therefore, you cannot 
expect measured results to exactly match the numbers listed.

Power depends on the impedance of the circuit. For example, if a filter has a nominal loss 
of 5 dB, straightforward probing on the input and output and then subtracting might not 
result in 5 dB because the input impedance could be different from the output imped-
ance. Most components in the RF section have the same input and output impedance 
(50ohms). Where this is not the case, absolute power is noted in the tables in dBm rather 
than loss or gain in dB.

Inject a CW tone into the receiver when testing the CDMA receiver. The gains and losses 
are the same for a CW signal as for the CDMA.