Figure 3-6. Gps Diagram - Motorola APX 5000 Service Manual

Basic Theory of Operation: Analog Mode of Operation
3.2.1.1 GPS
The GPS architecture employs a combination GPS/Bluetooth IC chip which decodes GPS signals at
1575.42 MHz. It is capable of producing a final position solution including full tracking and data
decode capability. The GPS receiver will operate in the autonomous mode only.
The GPS signal is tapped at the antenna port via a series resonant network which provides a very
low capacitive load to the transceiver. The signal is routed though a GPS LNA and it's output is
applied to the RF-Controller interface connector where it is eventually routed to the expansion board
for processing by the GPS/Bluetooth IC.
The GPS receiver is setup in an autonomous one track always (OTA) mode, also known as
continuous navigation. This means the GPS will continuously track satellites for as long as the radio
is powered to ensure the best possible accuracy. In the event the radio loses visibility of the satellites
due to terrain or environmental factors such as driving through a tunnel or entering a building, the
GPS will temporarily lose its position fix. A power savings algorithm will then cycle the GPS in and
out of a sleep mode at approximately 90 second intervals until the radio has moved back into an
environment where GPS signals are present.
The user will be able to view the current latitude, longitude, and time/date stamp on the radio's
display. The radio can also be configured to send its' location to the system at predetermined
intervals (LRRP). Depending on system options, the user may be able to enable/disable the GPS
receiver.
Antenna
3.2.1.2 VHF Front-End
From the RX/TX select switch, the VHF signal is routed to a pre-selector filter, followed by a Low
Noise Amplifier (LNA) and a second pre-selector filter. Both filters are discrete and fixed designs and
are used to band limit incoming energy and suppress known spurious responses such as image and
½ IF spur. The Mixer IC is also excited by a Local Oscillator (LO) signal at the LO port to down-
convert the RF signal to a 109.65 MHz intermediate frequency (IF). The down converted IF signal is
passed through a crystal filter and IF amplifier which drives the input of the Abacus 3 Analog to
Digital Converter IC (AD9864).
3.2.1.3 UHF1 Front-End
From the RX/TX select switch, a UHF1 signal is routed to the first pre-selector filter followed by an
LNA and a second pre-selector filter. Both filters are discrete and tunable designs and are used to
band limit the incoming energy and suppress known spurious responses such as Image spur. The
output of the second pre-selector filter is applied to the RF port of the Mixer IC. The Mixer IC is also
excited by a Local Oscillator (LO) signal at the LO port to down-convert the RF signal to a
109.65 MHz intermediate frequency (IF). The down converted IF signal is passed through a crystal
filter and IF amplifier which drives the input of the Abacus 3 Analog to Digital Converter IC (AD9864).
GPS Receiver Circuit

Figure 3-6. GPS Diagram

OMAP
Processor
GPS IC
Sec 1: 3-5