Motorola APX 1000 - Page 712

3-8 Theory of Operation: Main Board
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 (See Figure 3-6.)
• UHF1/UHF2 band (See Figure 3-7.)
• 700/800 MHz band (See Figure 3-8.)
Figure 3-6. Receiver Block Diagram (VHF)
Figure 3-7. Receiver Block Diagram (UHF1/UHF2 )
Antenna
Switch
15 dB Step
Attenuator
VHF VHF
IF Filter
DIG_CTRL_ATTH Rx LO
To GPS
Diplexer
SSI
18Mhz
CLK
Abacus III
ABACUS III
Dec.
Filter
ΣΔ ADC
2nd
LO
LO CLK
Harmonic
Filter
Antenna
Switch
15 dB Step
Attenuator
UHF UHF
IF Filter
DIG_CTRL_ATTH Rx LO
To GPS
Diplexer
SSI
18Mhz
CLK
Abacus III
ABACUS III
Dec.
Filter
ΣΔ ADC
2nd
LO
LO CLK
Harmonic
Filter