Rf Troubleshooting; 2112 General Troubleshooting Notes - Nokia RH-57 Series Troubleshooting Manual

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RF Troubleshooting

2112 General Troubleshooting Notes

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
pinpoint 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
information 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-
impedance 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.
Probing 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
impedance. 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.
Note: After opening the shield lids, always replace them with new lids.
Issue 1 07/2004
©2004 Nokia Corporation
Troubleshooting - RF
Company Confidential
2112 (RH-57)
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