Figure 3-5. Receiver Block Diagram (Vhf) - Motorola APX 5000 Service Manual

Theory of Operation: Transceiver Board
3.1.1.3 Antenna Port J101
Antenna port J101 is a surface-mount, miniature coaxial connector for the antenna cable.
3.1.1.4 Serial EEPROM
The electrically erasable programmable memory (EEPROM), U101, holds all of the transceiver
tuning data. This allows transceivers to be tuned in the factory and installed in the field without
retuning.
3.1.1.5 Power Conditioning Components
DC power-conditioning components include zener diodes, capacitors, ferrite beads, a power
inductor, and the fuse. Diodes VR200 and VR101 provide over-voltage protection. Ferrite beads
(designated E, etc.) and capacitors suppress electromagnetic interference from the transceiver.
The power-line filter consisting of L200, C202, and C203 suppresses digital noise from the VOCON
board switching power supplies that could degrade the transmitter spectral purity.
Ground clips M103 and M104 make contact between the transceiver board ground and the radio
chassis. The chassis connection is a necessary electrical reference point to complete the antenna
circuit path. Shields SH1 through SH14 appear on the schematic to show their connection to ground.
3.1.2 Receiver
In the VHF radio, the RF signal is received at the antenna and is routed through a Receive/Transmit
Multi Switch (SP3T). In the UHF1, UHF2 and 7/800 radio, the signal goes from the antenna and is
routed through an Auxiliary Switch before the Multi Switch (SP3T) IC. After the switch, the RF signal
passes through a diplexer circuit and a controllable external 15 dB attenuator. The output of the
attenuator leads to the receiver front end section.
• VHF band
• UHF1 and UHF2 bands
• 7/800 band
GPS
(See Figure 3-5.)
(See Figure
(See Figure 3-7.)
PER
DPLXR
SP3T
To
RF/Vocon
Connector

Figure 3-5. Receiver Block Diagram (VHF)

3-6.)
VHF
2nd
LO
SSI
ΣΔ ADC Dec.
Filter
18Mhz
LO CLK
CLK
Abacus III
3-7