Figure 3-4. Receiver Block Diagram (Vhf); Figure 3-5. Receiver Block Diagram (700/800 Mhz); Figure 3-6. Gps Diagram - Motorola APX 3000 Basic Service Manual

Basic Theory of Operation: Analog Mode of Operation
Antenna
Switch
DIG_CTRL_ATTH
Diplexer
Antenna
15 dB Step
Switch
Attenuator
DIG_CTRL_ATTH
Diplexer
3.2.1.1 GPS
The GPS signal is tapped at the antenna port via a series resonant network (diplexer) which provides
a very low capacitive load to the transceiver. The diplexer circuitry provides rejection to radio band
signals up to ~1GHz which serves as isolation between the radio RF and GPS signal paths. The
GPS signal is filtered though a GPS SAW filter - LNA – Saw filter chain before going into the TI GPS
IC for processing.
Antenna
Diplexer
15 dB Step
Attenuator
VHF

Figure 3-4. Receiver Block Diagram (VHF)

800
SW SW
700
To GPS

Figure 3-5. Receiver Block Diagram (700/800 MHz)

To Radio transceiver path
GPS Receiver Circuit

Figure 3-6. GPS Diagram

VHF
Rx LO
To GPS
800
SW SW
700
IF Filter
ABACUS III
ΣΔ ADC
2nd
LO
LO
Abacus III
IF Filter
ABACUS III
Rx LO
2nd
LO
LO
Processor
GPS IC
3-3
Dec.
SSI
Filter
18Mhz
CLK
CLK
Dec.
ΣΔ ADC SSI
Filter
18Mhz
CLK
CLK
Abacus III
OMAP