User Guide

Nokia Customer Care System Module
6015/6015i/6016i/6019i (RH-55), 6012 (RM-20)
Issue 1 - Revision 002 09/2004 ©2004 Nokia Corporation Company Confidential Page 31
The transmit chain is a direct conversion chain which contains the upconverter/driver
functionality, filters to reject unwanted harmonics and mixing products, and a power
amplifier.
The channel spacing for the PCS band is 50 kHz and for the AMPS/Cell band the spacing
is 30kHz. The baseband I/Q signals are converted directly to the desired RF frequency in
the upconverter stage. The local oscillator frequency is an integrated 4GHz oscillator. For
PCS operation, the local oscillator signal is divided by 2 while for AMPS/Cell operation
the local oscillator signal is divided by 4. The transmitter also contains three automatic
gain controls, which is used to vary the transmit power.
The following steps apply to the PCS and AMPS/Cell bands:
1. The differential RF outputs are combined into a single-ended output by an
external balun.
2. The signal is feed into a SAW filter, which provides the required Rx band
rejection.
3. The output of the filter is fed to a power amplifier, which also provides variable
gain control.
4. The output of the power amplifier is fed to the duplexer, which provides further
rejection of unwanted signals.
The power detector is placed at the antenna port of the duplexer, which means
that variation (over frequency and temperature) in the duplexer insertion loss is
automatically compensated.
5. The two frequency bands are then combined using a diplexer before going the
the external RF connector and the antennas.