Tx Vhf Vco; Uhf Synthesizer - Nokia RH-21 Series Troubleshooting Manual

CCS Technical Documentation

TX VHF VCO

The TX VHF VCO signal is used to generate transmitter Intermediate frequency. TX VHF
VCO has two fixed frequencies (361.08 MHz for lower band and 363.6 MHz for upper
band). Operating frequency is locked in Phase-locked loop and frequency is divided by
two before modulator.
Fault-finding chart for TX VHF VCO
AMPS, CH383
TDMA1900, CH1000
4
Check components:
C740, C741, C742, R741,
R742, R743 and
C749, C750, L750
3
Check resonator
components:
V744, C745, L746,
C747, C748

UHF Synthesizer

The UHF Synthesizer consists of an external 2GHz UHF VCO, loop filter and an integrated
PLL in the Safari RF IC. Safari T IC contains stages like counters, prescaler, divider by two,
phase and frequency comparator, and a charge pump circuit which allows two opera-
tional modes—analog and digital. The UHF VCO Oscillation frequency is from 2009.1MHz
to 2125.53 MHz.
In the upper band (TDMA1900), 2 GHz synthesizer frequency is fed straight to mixers. In
the lower band (AMPS and TDMA800), 2 GHZ UHF VCO frequency signal is first divided
by two inside Safari and then that divided signal is fed to mixers. The output frequency
Issue 1 05/2003 Confidential
-> TX VHF frequency 361.08 MHz
-> TX VHF frequency 363.6 MHz
5
Change
cascade amplifier
N750
OK
5.No OK
4.No
1
START HERE
Is oscillator locked
OK
to 361.08 MHz
3.No or 363.6 MHz
2.No
2
Check operating
voltage:
4.75 V
at R745
Nokia Corporation
6.No
OK
Yes
OK
No
L751, R745
OK
RH-21
Troubleshooting
6
Change
SAFARI
OK!
Check:
Page 37