Motorola APX 1000 Basic Service Manual page 167

Basic Theory of Operation: Analog Mode of Operation
3.2 Analog Mode of Operation
This section provides an overview of the analog mode receive and transmit theory of operation.
3.2.1 Receiving
The RF signal is received at the antenna and is routed through the Harmonic Filter, followed by the Antenna
Switch and finally the 15dB Step Attenuator IC. The latter contains a switchable attenuator that is enabled at
predetermined RF power thresholds present at the antenna port.
Antenna
15 dB Step
Switch
Attenuator
DIG_CTRL_ATTH
Diplexer
Antenna
15 dB Step
Switch
Attenuator
DIG_CTRL_ATTH
Diplexer
VHF
To GPS
Figure 3-2. Receiver Block Diagram (VHF)
UHF
To GPS
Figure 3-3. Receiver Block Diagram (UHF1/UHF2)
See Figure 3-2.
IF Filter
VHF
Rx LO
2nd
LO
IF Filter
UHF
Rx LO
2nd
LO
,
Figure 3-3 and Figure 3-4
ABACUS III
Dec.
ΣΔ ADC
Filter
LO CLK
Abacus III
ABACUS III
Dec.
ΣΔ ADC
Filter
LO CLK
Abacus III
3-3
.
SSI
18Mhz
CLK
SSI
18Mhz
CLK