Synthesizer Fault-Finding; 19.44 Mhz Reference Oscillator - Nokia RH-21 Series Troubleshooting Manual

RH-21
Troubleshooting
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Synthesizer fault-finding

There are four oscillators generating the needed frequencies for the RF section:
19.44 MHz reference oscillator, 2GHz UHF VCO, TX VHF cascade amplifier VCO, and
RX VHF VCO integrated in Safari. RX VHF frequency is fixed at 271.08 MHz and TX VHF
has two fixed frequencies: 361.08 MHz for lowband and 363.6 MHz for upper band. The
VCO operating frequencíes are controlled by the Safari PLL circuit. All locals are locked to
stable 19.44MHz reference oscillator.
The frequency range for 2GHz UHF VCO is 2009.1 ... 2125.53 MHz. The output frequency
range for the lower band is from 2009.1 to 2059.02 MHz. In upper band, the output fre-
quency range from the UHF VCO is from 2031.81 MHz to 2125.53 MHz.
A practical way to check out the synthesizer status is to measure control voltage of the
VCO from the Integrator capacitor. If voltage is stable and reasonable, local oscillators
are running correctly.

19.44 MHz reference oscillator

The 19.44 MHz oscillator frequency (G790) is controlled by UEM. This 19.44 MHz signal
is connected to Safari, PLL-circuits, and from Safari to UPP.
All synthesizers use divided VCTCXO signal as a reference signal for Phase-locked loop to
provide correct LO-frequency.
Baseband also needs a reference signal where it can generate the necessary clock signals
and VCTCXO output signal is also buffered and connected to UPP.
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Issue 1 05/2003