Service manual

2-11
transmit mode, the audio signal to be frequency modulated onto the carrier is received through U201
(pin 41).
When a high impedance is applied to U241 (pin 19), the VCO operates in BATTERY SAVER mode. In
this mode, both the receive and transmit oscillators as well as the receive transmit and prescaler
buffer are turned off.
Figure 2-9: UHF VCO Block Diagram
Table 2-5 Level Shifter Logic
Desired Mode AUX 4 AUX 3 TRB
Tx Low High (@3.2V) High (@4.8V)
Rx High Low Low
Battery Saver Low Low Hi-Z/Float (@2.5V)
Presc
RX
TX
Matching
Network
Low Pass
Filter
Attenuator
Pin 8
Pin 14
Pin 10
5V
(U201 Pin 28)
VCC Buffers
TX RF Injection
U201 Pin 32
AUX4 (U201 Pin 3)
AUX3 (U201 Pin 2)
Prescaler Out
Pin 12
Pin 19
Pin 20
TX/RX/BS
Switching Network
U241
VCOBIC
Rx Active
Bias
Tx Active
Bias
Pin 2
Rx-I adjust
Pin 1
Tx-I adjust
Pins 9,11,17
Pin 18
Vsens
Circuit
Pin 15
Pin 16
TX VCO
Circuit
TX
Tank
RX VCO
Circuit
RX
Tank
Pin 7
Vcc-Superfilter
Collector/RF in
Pin 4
Pin 5
Pin 6
RX
TX
(U201 Pin 28)
Rx-SW
Tx-SW
Vcc-Logic
(U201 Pin 28)
Steer Line
Voltage
(VCTRL)
Pin 13
Pin 3
TRB_IN
LO RF INJECTION
Level Shifter
Network