2-6
UHF (450-520 MHz) Frequency Synthesis
4.0
UHF (450-520 MHz) Frequency Synthesis
The synthesizer subsystem shown in Figure 2-3, consists of the reference oscillator (Y5261 or
Y5262), the Low Voltage Fractional-N synthesizer (LVFRAC-N, U5201), and the Voltage Controlled
Oscillator (VCO).
4.1
Reference Oscillator
The reference oscillator (Y5262) contains a temperature compensated crystal oscillator with a
frequency of 16.8 MHz. An Analog-to-Digital (A/D) converter internal to U5201 (LVFRAC-N) and
controlled by the µP via serial interface (SRL) sets the voltage at the warp output of U5201, pin 25 to
set the frequency of the oscillator. The output of the oscillator (Y5262, pin 3) is applied to pin 23
(XTAL1) of U5201 via an RC series combination.
In applications where less frequency stability is required, the oscillator inside U5201 is used along
with external crystal Y5261, varactor diode D5261, C5261, C5262, and R5262. In this case, Y5262,
R5263, C5235 and C5251 are not used. When Y5262 is used, Y5261, D5261, C5261, C5262 and
R5262 are not used, and C5263 is increased to 0.1 uF.
4.2
Fractional-N Synthesizer
The LVFRAC-N synthesizer IC (U5201) consists of a pre-scaler, programmable loop divider, control
divider logic, phase detector, charge pump, A/D converter for low frequency digital modulation,
balanced attenuator used to balance the high frequency analog modulation and low frequency digital
modulation, 13V positive voltage multiplier, serial interface for control, and a super filter for the
regulated 5 volts.
A voltage of 5V applied to the super filter input (U5201, pin 30) supplies an output voltage of 4.5 Vdc
(VSF) at pin 28. It supplies the VCO, VCO modulation bias circuit (via R5322), and synthesizer
charge pump resistor network (R5251, R5252). The synthesizer supply voltage is provided by 5V
regulator, U5211.
To generate a high voltage to supply the phase detector (charge pump) output stage at pin VCP
(U5701-32), a voltage of 13 Vdc is generated by the positive voltage multiplier circuit (D5201,
C5202, and C5203). This voltage multiplier is basically a diode capacitor network driven by two
signals (1.05MHz) 180 degrees out of phase (U5201, pins 14 and 15).
Summary of Contents for GM338
Page 1: ...GM328 GM338 GM398 Mobile Radios Detailed Service Manual 6804112J18 E December 2003 ...
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Page 7: ...GM328 GM338 GM398 Mobile Radios Service Maintainability Issue December 2003 ...
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Page 20: ...1 4 Radio Model Information THIS PAGE INTENTIONALLY LEFT BLANK ...
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Page 35: ...GM328 GM338 GM398 Mobile Radios Controlhead Service Information Issue December 2003 ...
Page 42: ...1 4 GM398 Model GCN6115_ THIS PAGE INTENTIONALLY LEFT BLANK ...
Page 56: ...2 14 Controlhead Model for GM398 THIS PAGE INTENTIONALLY LEFT BLANK ...
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Page 88: ...4 20 Controlhead GM398 PCB 8486178B03 Schematics THIS PAGE INTENTIONALLY LEFT BLANK ...
Page 89: ...GM328 GM338 GM398 Mobile Radios Controller Service Information Issue December 2003 ...
Page 114: ...2 2 Controller Troubleshooting Chart THIS PAGE INTENTIONALLY LEFT BLANK ...
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Page 141: ...GM328 GM338 GM398 Mobile Radios VHF 136 174MHz Service Information Issue December 2003 ...
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Page 187: ...GM328 GM338 GM398 Mobile Radios UHF 403 470MHz Service Information Issue December 2003 ...
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Page 275: ...GM338 GM398 Mobile Radios Low Band Service Information Issue December 2003 ...
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Page 379: ...GM338 Mobile Radios VHF 45W Bipolar 136 174MHz Service Information Issue December 2003 ...
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Page 411: ...GM338 Mobile Radios UHF1 40W Bipolar 403 470MHz Service Information Issue December 2003 ...
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Page 447: ...GM338 Mobile Radios UHF2 40W Bipolar 450 520MHz Service Information Issue December 2003 ...
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Page 483: ...GM338 Mobile Radio UHF B1 HIGH POWER LDMOS 403 470MHz Service Information Issue December 2003 ...
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