Motorola pro7100 Manuel de service Page 38

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2-24 Theory of Operation
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.
Figure 2-10. UHF VCO Block Diagram
The external RX buffers (Q4332) are enabled by a high at U4201 pin 3 (AUX4) via transistor switch
Q4333. In TX mode the modulation signal (VCOMOD) from the LVFRAC-N synthesizer IC (U4201
pin41) is applied to the modulation circuits CR4321, R4321, R4322 and C4324. These modulate the
TX VCO frequency via coupling capacitor C4321. Varactor CR4321 is biased for linearity from the
VSF.
Presc
RX
TX
Matching
Network
Low Pass
Filter
Attenuator
Pin8
Pin14
Pin10
(U4201 Pin28)
VCC Buffers
TX RF Injection
U4201 Pin 32
AUX3 (U4201 Pin2)
Prescaler Out
Pin 12Pin 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 Pin28)
Rx-SW
Tx-SW
Vcc-Logic
(U4201 Pin28)
Steer Line
Voltage
(VCTRL)
Pin13
Pin3
TRB IN
LO RF INJECTION
Q4301
Q4332
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