Example Signal Measured At Vcxo Output (R420); Vco - Nokia 2650 Service Manual

RH-53/54
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Example Signal Measured at VCXO output (R420)

Figure 20:Measured signal at VCXO output

VCO

The VCO is generating frequencies in the range of 3420.4MHz – 3839.2 MHz for the RH-53
and in the range 3296.8 to 3979.6 MHz for RH-54 when the PLL is running. The output frequen-
cy from the VCO is led to the Local oscillator input of the Mjoelner IC (N600), where the fre-
quency is divided either by 2 or 4 in order to generate all channels in EGSM and PCN
respectively. Frequency of the VCO is controlled by a DC-voltage (Vctrl) coming from the loop-
filter. The loopfilter consists of the components R618, R619 and C639-C641. Range of the Vctrl
when the PLL is running (locked) is 0.4V – 4.3V. Even if the PLL is not in locked state (Vctrl
out of range) there is some frequency at the output of the VCO (G600), which is between 3 and
4 GHz. This is true if the VCO is working and if the VCO power supply is at present (2.7V).
30 COMPANY CONFIDENTIAL Issue 2 06/2005
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