26 Mhz Reference Oscillator (Vcxo) - Nokia RH-47 Series Rf Description And Troubleshooting

RH-47
7 - RF Description and Troubleshooting
The setup should now look like this:
The frequency of 3920MHz at the output of the VCO (G701) has to be measured with an
RF probe and a spectrum analyzer.
The tuning voltage can be easily measured at the VC input of the VCO (C712) The tuning
voltage should be 3.2 .. 3.4V at f
typically 240MHz/V.
If this is not the case, then go to chapter Troubleshooting for PLL synthesizer.

26 MHz reference oscillator (VCXO)

The VCXO is integrated in the Mjoelner RF-ASIC (N601). The only external component is
the 26MHz crystal (B601).
The reference oscillator has two functions:
• Reference frequency for the PLL synthesizer.
• System clock for BB (RFClk = 26 MHz).
For an error free initial synchronization, the 26MHz frequency of the VCXO must be
accurate enough. Therefore, a VCXO-calibration value is written via the serial Bus into
the RefOSCCAL register of Mjoelner and an additional bit in the RefOSCCntl register of
the Mjoelner. That is necessary for the rough calibration of the VCXO.
The VCXO is fine tuned by programming the AFC value via the serial bus of Mjoelner. The
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= 3920.0MHz. The tuning sensitivity of the VCO is
VCO
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