HARRIS TR-307-X2 PRIVIATE RADIO BASESTATION User Manual

HARRIS CORPORATION PRIVIATE RADIO BASESTATION LBI 38643C 25 KHZ RECEIVER IF MODULE 19D902783G1

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Contents

user manual

TABLE OF CONTENTSPageDESCRIPTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Front CoverGENERAL SPECIFICATIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1CIRCUIT ANALYSIS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1INPUT MATCHING NETWORK . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1CRYSTAL FILTERS, IF AMPLIFIERS . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1OSCILLATOR/MIXER/DETECTOR . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1AUDIO AMPLIFIER . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1SQUELCH . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1Buffer Amplifier . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1High Pass Filter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2Noise Detector . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2DC Amplifier . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2Schmitt Trigger . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2FAULT DETECTOR . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2VOLTAGE REGULATOR . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2MAINTENANCE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2BLOCK DIAGRAM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2RECOMMENDED TEST EQUIPMENT . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2ALIGNMENT PROCEDURE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2TROUBLESHOOTING . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3ASSEMBLY DIAGRAM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3OUTLINE DIAGRAM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4SCHEMATIC DIAGRAM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5PARTS LIST . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7PRODUCTION CHANGES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8IC DATA . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9MAINTENANCE MANUAL FOR25kHz RECEIVER IF MODULE19D902783G1DESCRIPTIONThe MASTR III Receiver IF Module provides ampli-fication and demodulation of the 21.4 MHz IntermediateFrequency signal. The IF Module also includes the re-ceiver squelch circuitry. However, it does not include de-emphasis or squelch audio gating circuits. Figure 1 is ablock diagram showing the functional operation of theIF Module.The IF Module circuitry contains the following:•A 50 ohm input impedance matching network andIF Amplifier•A chain of two crystal filters and two integratedcircuit IF amplifiers•An integrated circuit containing a crystaloscillator, mixer, limiter, and quadrature detector•A variable gain AF amplifier•A squelch circuit•A fault detector circuit•An integrated circuit voltage regulatorLBI-38643CericssonzEricsson Inc.Private Radio SystemsMountain View RoadLynchburg, Virginia 245021-800-528-7711 (Outside USA, 804-592-7711) Printed in U.S.A.
CIRCUIT ANALYSISINPUT MATCHING NETWORKThe input impedance matching network provides a 50 ohmload for the receiver RF module. The network consists of C1thru C3, L1 thru L3, and R1.Capacitor C1 provides AC coupling and a DC block on theinput line (J1). This DC block protects the module in the eventof a failure in a preceding module. L2 and L3 are series reso-nant at 21.4 MHz and provide a signal path to the FET ampli-fier Q6. Parallel resonant circuit, L1 and C2, provide a path tothe 50 ohm load, R1, for frequencies other than 21.4 MHz.CRYSTAL FILTERS, IF AMPLIFIERSY1, Y2, U1, U2, and associated circuitry provide IF filter-ing and amplification at 21.4 MHz. Filters Y1 and Y2 are both4 pole bandpass filters with a center frequency of 21.4 MHzand a bandwidth of ±6.5 kHz. Amplifiers U1 and U2 are inte-grated circuit amplifiers. U1 provides 30 dB of gain, U2 pro-vides 18 dB of gain. The amplifiers and filters have terminalimpedances of 50 ohms. In circuit gain measurements can bemade using a high impedance probe.Inductors L3, L4 and associated resistors and capacitorsprovide power supply decoupling. R3 and R7 provide paths tothe input of the Fault Detector circuit. These inputs enable theFault Detector circuit to monitor the DC voltages of U1 andU2.The RF level detectors consist of transistors Q1 and Q2along with associated resistors and capacitors. These detectorsplay no role in the normal operation of the IF Module, but theyaid in unit testing and module troubleshooting.OSCILLATOR/MIXER/DETECTORIntegrated circuit U3 provides several functions including2nd mixer, if amplifier and limiter, and quadrature detector.The 20.945 MHz crystal oscillator provides local oscillatorinjection to the mixer in U3. This mixer converts the 21.4 MHzIF signal to 455 kHz. C20 and C21 are oscillator feedback ca-pacitors and have been chosen to provide the proper capaci-tance for crystal Y3. The proper oscillator output level isdifficult to measure directly without affecting the oscillation.A preferable measurement is at TP3 which should readabout 50 mV pk. (Measured using a 10 megohm, 11 pF oscil-loscope probe.)The mixer is internally connected to the crystal oscillator.Pins 16 and 3 of U3 are the mixer input and output respec-tively. Typical mixer conversion gain is about 20 dB. The out-put of the mixer drives the 4 pole ceramic bandpass filter FL1.The limiter input is U3 pin 5, but the limiter output is inter-nally connected to the detector and is not externally available.A received signal strength indicator (RSSI) is provided atU3 Pin 13. This indicator signal is generated within the limitercircuitry and provides an output current proportional to thelogarithm of the input signal strength. This current develops avoltage across R18. The voltage varies from about 0.7 Vdc fornoise input, to about 1 Vdc for a 12 dB SINAD signal, to amaximum of about 2.7 Vdc for a high signal level (50 dBstronger than that required for 12 dB SINAD).The quadrature detector provides a demodulated audio fre-quency output. The input to the detector is internally connectedto the limiter and is not externally available. The output of thedetector is U3 pin 9. R19 and C28 provide low-pass filtering toremove 455 kHz feedthrough. Ceramic resonator Y4 providesthe frequency selective component needed for FM demodula-tion. Y4 replaces the typical LC resonant circuit found in mostquadrature detectors. In contrast to the typical LC network, Y4requires no adjustment.The DC supply to U3 is provided through voltage droppingresistor R11 to U3 pin 4. R12 provides a path to the input ofthe Fault Detection circuit. This enables the Fault Detector tomonitor the DC voltage on U3.AUDIO AMPLIFIEROperational amplifier U6.3 provides audio frequency am-plification. Its gain is set by its associated resistors, includingvariable resistor VR1. VR1 allows for adjusting the AF outputlevel to 1 Vrms with a standard input signal to the module (1kHz AF, 3 kHz peak deviation). U6.2 is used as a voltage regu-lator to provide 4 Vdc for biasing the Operational amplifier.SQUELCHBuffer AmplifierIntegrated circuit U6.4 is configured as a unity gain bufferamplifier. It provides a high input impedance to minimize load-ing of the previous circuits.Copyright© February 1992, Ericsson Inc.TABLE 1 - GENERAL SPECIFICATIONSITEM SPECIFICATIONI.F. frequency 21.4 MHzInput Impedance 50 ohm12 dB SINAD -120.0 dBmAdj. CH SEL (25 kHz) -103 dBImage (20.49 MHz) -100 dB3rd order Intercept Pt 23 dBmVariation of Sensitivity with Signal Frequency 2 kHz2nd I.F. frequency 455 kHz2nd L.O. frequency 20.945 MHzAF output (J2 pin 31C) 1 Vrms adjustable (with standard input signal)AF output impedance 1k ohmAF distortion 5%AF response10 Hz -3 dB300 Hz ±1 dB1000 Hz 0 dB reference3 kHz ±1 dBHum & Noise -55 dBRSSI output (J2 pin 20C) 0.7 to 2.7 Vdc prop to log (sig level)RSSI time constant 5 msSQ Threshold Sensitivity -119 dBmSQ Maximum Sensitivity -102 dBmSQ Clipping 3 kHzSQ Attack 150 msSQ Close 250 msSQ output (J2 pin 26C) 5V logic (low = squelched)Fault output (J2 pin 11C) 5V logic (low = fault)DC Supply 1 Vrms (adjustable)LBI-38643C1
Highpass FilterThe audio frequency highpass filter consists of U7.1 and itsassociated circuitry. The purpose of this filter is to reject allvoice frequencies and allow only demodulated noise to pass.The functioning of the squelch circuit depends upon the pres-ence or absence of this noise. (When a signal is being received,i.e. the receiver is quiet, the squelch circuit senses the absenceof noise and unsquelches the radio.)Noise DetectorU7.2 along with associated components act as a noise de-tector. The rectified output of U7.2 charges C44 to a nearlyconstant DC voltage.DC AmplifierU7.3 is configured as a basic amplifier with a gain of 11.Schmitt TriggerU7.4 is configured as an amplifier with positive feedback.This arrangement provides hysteresis in the output verses inputcharacteristic. This eliminates the possibility of the squelch cir-cuit repeatedly cutting in and out when the input signal is neara threshold. R56 and R57 act as a voltage divider to provide a 5volt logic level output. (Logic High = unsqelched)FAULT DETECTORU4 and U5 are voltage comparators. These are configuredinto four "window detectors" which sense the presence of volt-ages within specified ranges (windows).The four window detector circuits are U4.1 & U4.2, U4.4& U4.3, U5.1 & U5.2, and U5.4 & U5.3. These monitor DCoperating voltages on U6.2, U1, U2, and U3 respectively. R29and R30 comprise a voltage divider to provide a 5 volt logiclevel output. A fault is indicated when the output drops to zero.Diode D1 and transistor Q3 monitor the output of the 8Vregulator. D1 is a 8.2 volt breakdown diode. If the regulatoroutput voltage should rise above 8.9 V (8.2 + 0.7 base-emitterdrop) Q1 will turn on and a fault will be indicated.Transistors Q4 and Q5 are drivers for the front panel LEDCR1. These are powered from the +13.8 Vdc line before the8V regulator. Therefore, if the regulator opens, a fault will stillbe indicated.VOLTAGE REGULATORU8 is a monolithic integrated circuit voltage regulator pro-viding 8 Vdc. This powers all circuitry in the module with ex-ception of the front panel LED and its drivers.MAINTENANCERECOMMENDED TEST EQUIPMENTThe following test equipment is required to test the IFModule.1. FM Signal Generator; HP 8640B, HP 8657A, orequivalent2. AF Generator or Function Generator3. Audio Analyzer; HP 8903B, HP 339A, or equivalent4. Oscilloscope5. DC Meter for troubleshooting6. Power Supply; 13.8 Vdc @ 150 mAALIGNMENT PROCEDURE1. Apply 13.8 Vdc supply to module.2. Verify DC current consumption is between 90 and 150mA.3. Verify fault output is 0 to 0.5 Vdc and front panel LEDis off.4. Apply a standard input signal to the module input. (-60dBm, 21.4 MHz signal modulated with 1kHz AF, 3 kHzpeak deviation) 5. Set VR1 for 1 Vrms ±3% at module output (pin 31C on96 pin connector J2).Figure 1 - 25 kHz Receiver IF ModuleLBI-38643C2
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Document ID5051
Application IDoGZpOmXjK/0HDgUw7lbp7w==
Document Descriptionuser manual
Short Term ConfidentialNo
Permanent ConfidentialNo
SupercedeNo
Document TypeUser Manual
Display FormatAdobe Acrobat PDF - pdf
Filesize544.41kB (6805166 bits)
Date Submitted1998-08-06 00:00:00
Date Available1998-10-05 00:00:00
Creation Date1997-08-16 15:54:55
Producing SoftwareAcrobat Distiller 3.0 for Windows
Document Lastmod1998-08-04 18:10:20
Document TitleLBI-38643C - 25 KHZ RECEIVER IF MODULE 19D902783G1
Document CreatorAdobe Printer Driver 3.0 for Windows 3.1
FCC ID Filing: AXATR-307-X2

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