Reference Oscillator 26 Mhz (Vctcxo); Fig 28 Typical Feature Tuning Curve For The Matshushita Vco - Nokia NPL-4 Series Troubleshooting Instructions

NPL-4/5/RM-104
Troubleshooting Instructions
The VCO frequency is twice the Rx frequency in the GSM1800 band:
= 2 * 1842.8 MHz = 3685.6 MHz. The VCO frequency shall be measured at
f = 2 * f
VCO RX
VCO output.
The tuning voltage can be easily measured at the Vc input of the VCO. The voltage shall
be measured at C503.
The tuning voltage should be 2.1V
The tuning sensitivity of the VCO is typically 250MHz/V. The typical relation of VCO fre-
quency and tuning voltage is shown in the following diagram:
Figure 28: Typical Feature Tuning Curve for the Matshushita VCO
4500
4000
3500
3000
0
If the frequency or the tuning voltage have other values than given above, then go to
chapter Fault finding chart for PLL synthesizer.

Reference oscillator 26 MHz (VCTCXO)

The reference oscillator is implemented as Voltage Controlled Temperature Compensated
Crystal Oscillator (VCTCXO) module. The component (G501) is located in the Small Signal
chamber.
The reference oscillator has two functions:
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DC
Temperature: +25°C
0.5 1 1.5 2 2.5
2.55V @ 24.4 .. 25.4°C
High limit
.. 2.6V
at f = 3685.6MHz.
DC VCO
3 3.5 4 4.5
VCTRL [V]
2.7V @ 24.4 .. 25.4°C 2.85V @ 24.4 .. 25.4°C
Low limit
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