Nokia 2220 Servicehandbuch

RH-42

Troubleshooting Instructions

CCS Technical Documentation

Page 28

 Nokia Corporation          Confidential

Issue 2 09/2003

There are four oscillators generating the needed frequencies for RF section: 19.44 MHz 
VCTCXO is used as a reference signal oscillator reference oscillator, 2 GHz UHF VCO with 
loop filter circuit is used for RX and TX channel selection, TX VHF and RF VHF are for TX 
modulator, and 2nd RX mixer locals generation. 

The VHF synthesizers are integrated in Taco, but have external VCO coils and loop filters.  
RX VHF frequency is fixed 271.08 MHz and TX VHF is fixed to 271.08 MHz . All locals are 
locked to stable 19.44 MHz reference oscillator.

The frequency range for 2 GHz UHF VCO is: 2009.1 MHz … 2125.53 MHz. The output fre-
quency range for the lower band is from 2009.16 MHz to 2059.02 MHz.

A practical way to check out synthesizer status is by measuring control voltage of the 
VCO from the Integrator capacitor. If voltage is stable and reasonable, local oscillators 
are running correctly.

The VCTCXO oscillator frequency (G790) is controlled by UEM. This output 19.44 MHz 
signal is connected to Taco. It is used as a reference signal in Taco and also fed out as 
buffered clock signal to UPP. All synthesizers use divided 19.44 MHz signal as a reference 
signal for Phase locked loop to provide correct LO frequency. 

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