2-8
UHF (403-470 MHz) Frequency Synthesis
4.3
Voltage Controlled Oscillator (VCO)
The Voltage Controlled Oscillator (VCO) consists of the VCO/Buffer IC (VCOBIC, U4301), the TX
and RX tank circuits, the external RX buffer stages, and the modulation circuitry.
Figure 2-4 UHF VCO Block Diagram
The VCOBIC together with Fractional-N synthesizer (U4201) generates the required frequencies in
both transmit and receive modes. The TRB line (U4301 pin 19) determines which tank circuits and
internal buffers are to be enabled. A high level on TRB enables TX tank and TX output (pin 10), and
a low enables RX tank and RX output (pin 8). A sample of the signal from the enabled output is
routed from U4301 pin 12 (PRESC_OUT), via a low pass filter, to pin 32 of U4201 (PREIN).
A steering line voltage (VCTRL) between 3.0V and 10.0V at varactor diode CR4311 will tune the full
TX frequency range (TXINJ) from 403 MHz to 470 MHz, and at varactor diodes CR4301, CR4302
and CR4303 will tune the full RX frequency range (RXINJ) from 358 MHz to 425 MHz. The tank
circuits uses the Hartley configuration for wider bandwidth. For the RX tank circuit, an external
transistor Q4301 is used in conjunction with the internal transistor for better side-band noise.
Presc
RX
TX
Matching
Network
Low Pass
Filter
Attenuator
Pin8
Pin14
Pin10
(U4201 Pin28)
VCC Buffers
TX RF Injection
U4201 Pin 32
AUX3 (U4201 Pin 2)
Prescaler Out
Pin 12
Pin 19
Pin 20
TX/RX/BS
Switching Network
U4301
VCOBIC
Rx
Active Bias
Tx
Active Bias
Pin2
Rx-I adjust
Pin1
Tx-I adjust
Pins 9,11,17
Pin18
Vsens
Circuit
Pin15
Pin16
RX VCO
Circuit
TX VCO
Circuit
RX Tank
TX Tank
Pin7
Vcc-Superfilter
Collector/RF in
Pin4
Pin5
Pin6
RX
TX
(U4201 Pin 28)
Rx-SW
Tx-SW
Vcc-Logic
(U4201 Pin 28)
Steer Line
Voltage
(VCTRL)
Pin13
Pin3
TRB IN
LO RF INJECTION
Q4301
Q4332
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 ...
Page 32: ...2 12 Notes For All Schematics and Circuit Boards THIS PAGE INTENTIONALLY LEFT BLANK ...
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 ...
Page 140: ...3 26 Controller T7 T9 Schematic Diagrams THIS PAGE INTENTIONALLY LEFT BLANK ...
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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