Analog Mode Of Operation; Figure 3-3. Receiver Block Diagram (Vhf And 700-800 Mhz); Figure 3-4. Receiver Block Diagram (Uhf1 And 700-800 Mhz) - ASTRO APX 7000 Basic Service Manual

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 Auxiliary and Multi Switch (SP3T)
ICs. The latter contains a switchable attenuator that is enabled at predetermined RF power
thresholds present at the antenna port. The output of the Multi-switch IC is applied to the first SPST
band select switch to select either VHF or 700–800 bands
(see Figure 3-4), VHF or UHF1 bands
UHF2 or 700–800 bands
RMT Port
AUX
RMT Port
AUX
(see Figure
PER SW
DPLXR
SP3T 2:1
To
RF/Vocon
Connector
Figure 3-3. Receiver Block Diagram (VHF and 700–800 MHz)
PER SW
DPLXR
SP3T 2:1
To
RF/Vocon
Connector
Figure 3-4. Receiver Block Diagram (UHF1 and 700–800 MHz)
(see Figure
(see Figure 3-5), UHF1 or UHF2 bands
3-7) and VHF or UHF2 bands
700/800
VHF
2nd
LO
700/800
UHF1
2nd
LO
3-3), UHF1 or 700–800 bands
(see Figure
(see Figure 3-8).
SW
2:1
SSI
ΣΔ ADC Dec.
Filter
18Mhz
LO CLK
CLK
Abacus III
SW
2:1
SSI
ΣΔ ADC Dec.
Filter
18Mhz
LO CLK
CLK
Abacus III
Sec 1: 3-3
3-6),