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RA-2/3
7 - RF Description and Troubleshooting
RF Troubleshooting
All measurements should be done using a spectrum analyzer with a high-frequency high-im-
pedance passive probe (LO-/reference frequencies and RF power levels) and an oscilloscope
with a 10:1 probe (DC-voltages and low frequency signals).
The RF section is build around one RF ASIC (HELGO N7500). For easier troubleshooting, this
RF troubleshooting document is divided into sections.
Before changing HELGO, please check that both supply voltages and serial communication
coming from baseband to HELGO are OK. Please note that the grounding of the PA module is
directly below the PA module, so it is difficult to check or change.
Most RF semiconductors are static discharge sensitive! Therefore ESD protection must be tak-
en care of during repair (ground straps and ESD soldering irons). HELGO and PA are moisture
sensitive so parts must be pre-baked prior to soldering.
Apart from key components described in this document there are a lot of discrete components
(resistors, inductors and capacitors) of which troubleshooting is done by checking if the solder-
ing of the component is done properly (for factory repairs checking if it is missing from the
PWB). You can check capacitors for shortening and resistors for value by means of an ohm-
meter, but be aware in-circuit measurements should be evaluated carefully.
Please be aware that all measured voltages or RF levels in this document are rough figures.
Especially RF levels vary due to different measuring equipment or different grounding of the
probe used. When using an RF probe use a pair of metallic tweezers to connect the probe
ground to the PWB ground as close to the measurement point as possible.
Receiver description and troubleshooting
Each receiver path is a direct conversion linear receiver. From the antenna, the received RF-
signal is fed to a front end module where a diplexer first divides the signal into two separate
paths according to the band of operation: either lower, GSM850/EGSM900 or upper,
GSM1800/GSM1900 path.
Most of the receiver circuitry is included in Helgo.
Rx front end
The front end features include:
•
Antenna 50 ohm input
•
RXs single outputs
•
TXs single 50 ohm inputs
•
3 control lines from Helgo
Antenna
The RA-2/3 GSM850/EGSM900/GSM1800/GSM1900 transceiver features an internal anten-
na. There are two triple-band antennas: one for RA-2 and one for RA-3.
Issue 1 09/04
COMPANY CONFIDENTIAL
Copyright © 2004 Nokia. All Rights Reserved.
Nokia Customer Care
17
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Troubleshooting
