6881094C31-E
November 16, 2006
Theory of Operation:
Transceiver Board
3-11
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 discrete, the pass band is up to 470 MHz, and the stop band is
above 760 MHz.
UHF Range 2:
The harmonic filter uses discrete components. The pass band is up to 595 MHz, and
the stop band is above 900 MHz.
700–800 MHz:
The harmonic filter uses both discrete components and transmission lines. The pass
band is up to 870 MHz, and the stop band is above 1500 MHz.
3.1.3.7 RF Detectors D101 and D102
Two Schottky diodes, D101 and D102, are used as forward- and reverse-power detectors. Forward-
coupled RF from the power amplifier, and reverse-coupled RF from the antenna are converted to DC
voltages FWD and RVS. Detector output is a positive DC voltage, proportional to the amplitude of
the RF signal at the input.
3.1.3.8 Summing Amplifier U106
This op-amp circuit is a non-inverting buffer. Signals FWD and RVS are summed and sent to the
ALC input of the PCIC. When the antenna port is loaded with a low VSWR (voltage standing wave
ratio), as in normal operation, RVS is far less than FWD, the amplifier output is a function of FWD,
and the radio maintains a constant output power. Under high VSWR conditions, such as when the
antenna is damaged or held near a large metal surface, the amplitude of RVS becomes a large
fraction of FWD, the amplifier output increases proportionally, and the radio cuts back the transmitter
power by up to 50%. This reduces high battery current into a large VSWR transmitter to extend
battery life.
3.1.3.9 Power-Control IC (PCIC) U104
The PCIC, U104, contains all of the digital, and most of the analog, circuits needed to control the
transmitter power amplifier. Host control is through a 3-wire, smart SPI interface. Pin descriptions are
shown in
Table 3-3. Power Control IC (U104) Pin Descriptions
Pin
Name
Description
1
RFIN
Detector voltage input to ALC
2
T1
Test point
3
CI
External capacitor for integrator time constant
4
INT
Integrator output; control voltage to amplifiers
5
CJ
External capacitor for PA rise and fall times
6, 7
VL, CL
External capacitor for PA rise and fall times
8
GND1
Ground
Summary of Contents for ASTRO XTS-5000
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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 ...