Uhf1 Voltage Control Oscillator (Vco); Figure 2-7. Uhf Vco Block Diagram - Motorola PR860 Detailed Service Manual

2-10
2.7

UHF1 Voltage Control Oscillator (VCO)

Rx-SW
Tx-SW
(U201 Pin28)
VSF
Steer Line
Voltage
(VCTRL)
RX VCO
RX Tank
Circuit
TX VCO
TX Tank
Circuit
The VCOBIC (U241) in conjunction with the Fractional-N synthesizer (U201) generates RF in both the
receive and the transmit modes of operation. The TRB line (U241 pin 19) determines which oscillator
and buffer will be enabled. A sample of the RF signal from the enabled oscillator is routed from U241
pin 12, through a low pass filter, to the prescaler input (U201 pin 32). After frequency comparison in
the synthesizer, a resultant CONTROL VOLTAGE is received at the VCO. This voltage is a DC
voltage between 3.5V and 9.5V when the PLL is locked on frequency.
Pin 20
Pin7
TX/RX/BS
Pin13
Switching Network
Vcc-Superfilter
Pin3
Collector/RF in
Pin4
RX
Active Bias
Pin5
Pin6
TX
Active Bias
Pin16
Pin15
Vsens
Circuit
Pin18
Vcc-Logic
VSF
(U201 Pin28)

Figure 2-7. UHF VCO Block Diagram

Theory of Operation: UHF1 Voltage Control Oscillator (VCO)
Level Shifter
Network
Prescaler Out
TRB_IN
Pin 19 Pin 12
Presc
U241
VCOBIC
RX
Rx
Tx
TX
Pin2 Pin1 Pins 9,11,17
Tx-I adjust
Rx-I adjust
5V
AUX3 (U201 Pin2)
AUX4 (U201 Pin3)
U201 Pin 32
LO RF INJECTION
Matching
Network
Pin8
VSF
(U201 Pin28)
Pin14
VCC Buffers
TX RF Injection
Pin10
Attenuator
Low Pass
Filter