Nokia RM-235 Service Manual page 146

1.1. Cellular antenna description
• The phone has one main Cellular antenna covering all GSM and WCDMA bands
• The antenna is located at the bottom of the product in the keypad area
• The antenna comprises a plastic antenna carrier and a flexi circuit foil. The antenna has 2 connections,
one is the feed to the antenna the other is a ground connection for a parasitic element
1.2. Cellular antenna fault finding
• The antenna can be checked using the RF test coupler provided. The measurement should be compared
to a known working phone. Make the comparison at the GSM1800 band (any freq point will do).
• Please refer to the section on testing using a coupling jig below for more detailed information on good
testing techniques
2. Recommendations for using an RF coupler
All coupler measurements should be done as a relative measurement (i.e. compared with a known working
phone). An RF coupler is a radiated measurement; as such objects near the measurement can change the
results.
Anything metallic or lossy will alter the results if placed nearby including the following;
• Hands
• Antistatic mats
• Antistatic bags
• Metal including tools and table legs etc.
You need to put the test jig on something like a bench or an antistatic mat. This does not matter as long as
the jig is kept in the same place as when the reference measurement was done.
To perform a series of measurements do a reference measurement on a known working phone and note
down the coupling loss. Then do measurements on the phones under test and compare it to the reference
phone. Repeat the reference meas every time you move the jig or if you start to see drift in the results.
The antenna under test should be within 3dB of the reference antenna using the method described above.
If it is not repeat the reference measurement to check, then check the RF output power.
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Figure 35 Cellular antenna
COMPANY CONFIDENTIAL
Copyright © 2008 Nokia. All rights reserved.
RM-235
RF troubleshooting
Issue 1