November 16, 2006
6881094C31-E
3-8
Theory 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 pF capacitance at the Abacus input IFIN. Formatted SSI
data is output to the VOCON board on ports FS, DOUTA, and CLKOUT.
3.1.2.2.2 Second Local Oscillator
The second LO is controlled by the Abacus LO synthesizer, which mixes with IFIN to produce a
2.25 MHz final IF. The external VCO consists of Q502 and its bias network and frequency-
determining elements. Signal FREF is the 16.8 MHz reference from the FGU. Darlington transistor
Q501 with C550 and R501 form an active power-line filter.
VHF:
The second LO frequency is 42.6 MHz by default, or 47.1 MHz in special cases as needed to
avoid radio self-quieters. The loop filter is composed of R507, C558, C559, and C503.
UHF Range 1:
The second LO frequency is 71.1 MHz by default or 75.6 MHz in special cases as
needed to avoid radio self-quieters. The loop filter is composed of R551, C558, C559, R552, and
C512.
UHF Range 2:
The 2nd LO frequency is 71.1 Mhz. C558, R507, and C559 form the loop filter.
700–800 MHz:
The second LO frequency is 107.4 MHz by default or 111.9 MHz in special cases as
needed to avoid radio self-quieters. The loop filter is composed of R507, C558, C559, R505, and
C512.
3.1.2.2.3 Sampling Clock Oscillator
The Abacus sampling clock synthesizer operates at 18 MHz = 8 x 2.25 MHz. The VCO uses an
internal transistor and external resonator. The resonator is composed of L503, C535, and D501.
VHF:
The loop filter is composed of R514, C536, C570, and C571.
UHF Range 1 and 700–800 MHz:
The loop filter is composed of R514, C570, and C571.
UHF Range 2:
C503, C536, R415, C570, and C571 form the loop filter.
3.1.3
Transmitter
The transmitter takes modulated RF from the FGU and amplifies it to the radio's rated output power
to produce the modulated transmitter carrier at the antenna.
NOTE:
Refer to
Table 8-1, “List of Transceiver Schematics and Board Overlays,” on page 8-1
for a
listing of transmitter-related schematics that will aid in the following discussion.
The transmitter (
) consists of an RF driver IC that receives its input signal
from the voltage-controlled oscillator (VCO) and a high-power output transistor. Transmitter power is
controlled by a power-control IC (PCIC) that senses the output of a directional coupler and adjusts
PA control voltages to maintain a constant power level. The signal passes through an antenna switch
and harmonic filter to the antenna.
Summary of Contents for ASTRO XTS-5000
Page 7: ...vi Table of Contents November 16 2006 6881094C31 E Notes ...
Page 11: ...x List of Figures November 16 2006 6881094C31 E Notes ...
Page 17: ...November 16 2006 6881094C31 E xvi CommercialWarranty Notes ...
Page 31: ...November 16 2006 6881094C31 E xxx Portable Radio Model Numbering System Notes ...
Page 83: ...November 16 2006 6881094C31 E 3 44 Theory of Operation Encryption Module ...
Page 135: ...November 16 2006 6881094C31 E 5 44 Troubleshooting Charts Secure Hardware Failure Notes ...
Page 175: ...November 16 2006 6881094C31 E 7 32 Troubleshooting Tables List of Board and IC Signals Notes ...
Page 367: ...November 16 2006 6881094C31 E Glossary 10 Notes ...
Page 373: ...Index 6 November 16 2006 6881094C31 E Notes ...
