Motorola APX 1000 Detailed Service Manual page 712

3-8
3.1.2 Receiver
The RF signal is received at the antenna and is routed through the Harmonic Filter, followed by the
Antenna Switch and the 15dB Step Attenuator IC. The latter contains a switchable attenuator that is
enabled at predetermined RF power thresholds present at the antenna port. The output of the
attenuator leads to the receiver front end section.
• VHF band
• UHF1/UHF2 band
• 700/800 MHz band
Antenna
Switch
Harmonic
Filter
Diplexer
Antenna
Switch
Harmonic
Filter
Diplexer
(See Figure 3-6.)
(See Figure 3-7.)
(See Figure 3-8.)
15 dB Step
Attenuator
VHF
DIG_CTRL_ATTH
Figure 3-6. Receiver Block Diagram (VHF)
15 dB Step
Attenuator
UHF
DIG_CTRL_ATTH
Figure 3-7. Receiver Block Diagram (UHF1/UHF2 )
IF Filter
VHF
Rx LO
To GPS
IF Filter
UHF
Rx LO
To GPS
Theory of Operation: Main Board
ABACUS III
Dec.
ΣΔ ADC
Filter
2nd
LO CLK
LO
Abacus III
ABACUS III
Dec.
ΣΔ ADC
Filter
2nd
LO CLK
LO
Abacus III
SSI
18Mhz
CLK
SSI
18Mhz
CLK