Motorola Astro Xts5000 Detailed 6881094c31 E Manual

November 16, 20066881094C31-E
3-2Theory of Operation: Transceiver Board
Figure 3-1.  XTS 5000 Overall Block Diagram
3.1 Transceiver Board
The transceiver (XCVR) board performs the transmitter and receiver functions necessary to translate 
between voice and data from the VOCON board and the modulated radio-frequency (RF) carrier at 
the antenna. The transceiver board contains all the radio’s RF circuits for the following major 
components:
• Receiver
• Transmitter
• Frequency Generation Unit (FGU)
Figure...

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Figure 3-3.  Transceiver (UHF Range 1, UHF Range 2 and 700–800 MHz) Block Diagram 
(Power and Control Omitted)
3.1.1 Interconnections
This section describes the various interconnections for the transceiver board.
3.1.1.1  Battery Connector J3
Battery connector J3 consists of three gold-plated contacts on the printed circuit board that mate with 
a B-plus connector assembly. Signal descriptions are in Table 3-1.
3.1.1.2  VOCON...

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3-4Theory of Operation: Transceiver Board
Table 3-2 lists the connector pins, their signals, and functions. SPI refers to serial peripheral 
interface, which is the control bus from the microprocessor. SSI is the serial synchronous interface 
bus for data to and from the DSP. There is a RX SSI bus for demodulated data from the receiver and 
a TX SSI bus for modulation data to the transmitter.
Table 3-2.  VOCON Connector P1
Pin 
No.VOCON SignalXCVR 
SignalXCVR 
I/OTy p...

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3.1.1.3  Antenna Port J2
Antenna port J2 is a surface-mount, miniature coaxial connector for the antenna cable.
3.1.1.4  Serial EEPROM
The serial, electrostatically erasable, programmable, read-only memory (EEPROM), U907 in VHF 
and 700–800 MHz or U4 in UHF Range 1, 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...

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3-6Theory of Operation: Transceiver Board
3.1.2.1  Receiver Front End
NOTE:Refer to Table 8-1, “List of Transceiver Schematics and Board Overlays,” on page 8-1 for a 
listing of receiver front end schematics.
The receiver front end tunes to the desired channel and down converts the RF signal to the first 
intermediate frequency (IF). Channel selection is by way of a tunable local oscillator, RXLO, from the 
FGU.
The receiver front end consists of a preselector filter, an RF...

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3.1.2.2  Receiver Back End
The receiver back end, which consists of the Abacus III (AD9874 IF digitizing subsystem) IC and its 
associated circuitry, processes the down-converted IF signal to produce digital data for final 
processing by the VOCON DSP.
NOTE:Refer to Table 8-1, “List of Transceiver Schematics and Board Overlays,” on page 8-1 for a 
listing of receiver back end schematics.
3.1.2.2.1  Abacus III IC U500
The AD9874...

November 16, 20066881094C31-E
3-8Theory of Operation: Transceiver Board
UHF Range 1: Input signal RXIF is 73.35 MHz. Components L547 and C547 match the input 
impedance to 50 ohms.
UHF Range 2: Input signal RXIF is 73.35 MHz. L542, C515, and C547 match the Ababcus input to 
50 Ohms.
700–800 MHz: Input signal RXIF is the 109.65 MHz IF from crystal filter FL403 in the receiver front 
end. Components L547 and C542 match the input impedance from 50 ohms at RXIF to 
approximately 420 ohms in parallel with a 1...

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Figure 3-6.  Transmitter Block Diagram
3.1.3.1  Power Distribution
To minimize voltage drop to the power amplifiers, net RAWB+ connects to power module Q107 and 
the second stage of driver amplifier U102 through components having minimal series resistance—
ferrite beads and chokes only. During receive, no RF or DC bias is applied, and leakage current 
through U102 and Q107 is less than 100 microamps. The first stage of U102 uses less...

November 16, 20066881094C31-E
3-10Theory of Operation: Transceiver Board
3.1.3.3  Power Amplifier Transistor Q107
The power amplifier transistor, Q107, is an LDMOS FET housed in a high-power, surface-mount, ring 
package. To prevent thermal damage, it is essential that the heat sink of the power module be held in 
place against the radio chassis. The input impedance-matching network uses discrete inductors and 
capacitors. The low-pass output matching network uses both transmission lines and lumped LCs....

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3.1.3.6  Harmonic Filter
The harmonic filter is a high-power, low-loss, low-pass filter. Its purpose is to suppress transmitter 
harmonics. The filter also improves receiver out-of-band rejection. Shield SH700 must be in place to 
achieve the required stop band rejection.
VHF: The harmonic filter uses discrete components. The pass band is up to 190 MHz, and the stop 
band is above 260 MHz.
UHF Range 1: The harmonic filter is...