Gsm (Gmsk) Modulation Spectrum Ok - Nokia RM-42 Service Manual

Appendix A: RF Troubleshooting
3.3.5.1.1 C7560, C7513, C7526 and C2214 ok?
• Check that components are in place and solder joints are ok
• Disconnect the power supply from the phone and use an ohmmeter to find out if the VXO-line is
short-circuited to the ground. If short-circuit is found replace C7560, C7513, C7526 and C2214. If
replacing does not help then go to the next steps.
3.3.5.1.2 Replace Retu
3.3.5.1.3 Replace Hinku (N7500) or Vinku (N7501) or VCTCXO (G7501) or all three components
3.3.5.2 BB AFC-voltage ok?
See section
•
3.3.5.3 Replace VCTCXO G7501

3.4 GSM (GMSK) modulation spectrum ok?

• GSM transmitter has to be active before measurements. Procedure is explained in section
"Transmitter troubleshooting".
Measurement can be done with a GSM transmitter tester or other GSM communication tester.
•
Settings have to be done according to the 3GPP specifications. Modulation spectrum
measurement is possible to perform also with a spectrum analyser, but in this case measurement
settings have to be done manually.
• Attach the phone to the product specific test jig and the RF-test device to the RF-coupler. Coupler
attenuation should be also taken into account during measurements.
Set TX Data Type to "Random" in Phoenix
-
Enter correct "Centre frequency" to the spectrum analyser (see section "Frequency mappings") and
-
"Span" should be set to 2 MHz. "RBW" and "VBW" should be set to 30 kHz.
Select a correct attenuator in the spectrum analyser and set "reference level offset" according
-
attenuation between the phone and the spectrum analyser.
Enter "Sweep time" at least to 2.5 s.
-
Check that the TX power is not over the specification limits in following offsets (tables below). If
-
the measurement is performed with a spectrum analyser according above settings then there may
be 1 to 3 dB exceeding with some limit values. This is caused because above settings are meant
only for fast modulation spectrum checking and are not exactly done according 3GPP specification.
EGSM900/GSM1800:
Offset (kHz)
Limit (dBc)
"BB AFC-voltage ok?"
100 200
+0,5 -30
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