Receiver Front-End; Vhf (136-174 Mhz) Band; Figure 3-12. Dc Voltage Routing Block Diagram (Vhf And 700-800 Mhz) - Motorola ASTRO Digital XTL 5000 Detailed Service Manual

Theory of Operation: Receiver Front-End
Control Head
On/Off SIOIC
Figure 3-12. DC Voltage Routing Block Diagram (VHF and 700–800 MHz)
The 9.3 V and the A+ voltage are the main DC power for the RF section. The 9.1 V (referred to as
"keyed 9.1 V") is controlled by the VOCON board through P501, pin 45. This DC voltage enables the
transmitter's RF power amplifier when the VOCON board senses a lock detect from the synthesizer.
3.4

Receiver Front-End

This section provides a detailed circuit description of receiver front-end (RXFE). When reading the
Theory of Operation, refer to your appropriate schematic and component location diagrams located
in "Chapter 7. Schematics, Component Location Diagrams, and Parts
operation will help isolate the problem to a particular component.
3.4.1 VHF (136–174 MHz) Band
The receiver circuits primary duties are to detect, filter, amplify, and demodulate RF signals in the
presence of strong interfering noise and unintended signals. The receiver is broken down into the
following blocks
• Front-end, which includes:
- 15 dB step attenuator
- PIN diode switches
- Three discrete filters
- Two low-noise amplifiers
- Mixer
• Back-end, which includes:
- Two crystal filters
6881096C74-B
J0401
A+ 19, 21
FET
Q0503
SWB+ 17
9.3V
Regulator
U0500
5V
Regulator
U0503
3.0V 2.85V
1.85V
Regulator Regulator
Regulator
U0962 U0501
U0507
Controller Section
IGN 20
(Figure 3-13 on page 3-14):
UNSW
A+
5V Circuit
VR0500, R0507
SW_A+
9.33V
Regulator
U0950
9.3V_FGU
5V
VCC5
Regulator
U0505
1.55V 3V
3V
Regulator Regulator Regulator
U0502 U6750
U6002
RX / FGU Section
UWW_5V
J0950
J0402 J2
20, 22 24
9.3V
Regulator
U0951
KEYED_9.1_EN
9.3V_TX
Switch
GPIO
TX Section
18 25
MAEPF-27825-O
Lists". This detailed theory of
May 25, 2005
3-13
SWB+