Synthesizer: Lo1 - Siemens S55 Repair Documentation

4.2.2

Synthesizer: LO1

The first local oscillator is needed to generate frequencies which enables the
transceiver IC to demodulate the receiver signal and to perform the channel selection
in the TX part. To do so, a control voltage for the LO1 is used. Gained by a
comparator. (located inside the Transceiver (Bright -IC)). This control voltage is a
result of the comparison of the divided LO1 and the 26MHz reference Signal. The
division ratio of the dividers is programmed by the EGOLD+, according to the network
channel requirements.
The first local oscillator (LO1) consists of the PLL
external loop filter and the VCO (Z850) module. This LO1 circuit generates
frequencies from
3700-3980 MHz for EGSM900
3580-3760 MHz for GSM1800
3860-3980 MHz for GSM1900
Formula to calculate the TX frequencies:
EGSM900
Channel: 975...1023/76...92
Channel: 0...75/93...124
GSM1800
Channel: 512...661
Channel: 662...885
GSM1900
Channel: 512...810
Formula to calculate the RX frequencies:
EGSM900 = Channel freq. * 4
GSM1800 = Channel freq. * 2
GSM1900 = Channel freq. * 2
V1.00
S55/S57
= (Channel freq. + 82MHz) * 4
= (Channel freq. + 80MHz) * 4
= (Channel freq. - 80MHz) * 2
= (Channel freq. - 82MHz) * 2
= (Channel freq. – 80MHz) * 2
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26MHz
inside the Bright (D800), an
ICM MP CCQ GRM
12/02