EFJohnson 7780 service manual LOW-PASS Filter IC205A/B, Smartnet Data Processing

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CIRCUIT DESCRIPTION

caused by high input levels from the internal or external microphone. The bias voltage to this stage and also to IC201A is produced by voltage divider R208/R207.

4.8.3 LOW-PASS FILTER (IC205A/B)

IC205A and IC205B form a low-pass splatter filter which attenuates frequencies above approxi- mately 3 kHz. This prevents adjacent channel interfer- ence caused by the harmonic frequencies which result from amplitude limiting.

The output signal from this filter is applied to IC209 which contains four logic-controlled potentio- meters. The transmit audio signal is applied to potenti- ometer 3 on pin 20 and fed out on pin 19 which is the wiper of that potentiometer. The potentiometers in this device are adjusted by the control logic via the serial data bus (MSCK/MSO). The transmit audio/DTMF level is set when the transceiver is aligned.

The transmit audio/DTMF signal is then fed to IC201 where it is combined with the transmit data/ SMARTNET data signal if applicable. The output signal on pin 4 of IC201 is then fed to the VCO in the RF unit and also to pins 7 and 8 of IC209. The signal fed to the RF unit (MOD) modulates the VCO, and the signal fed to IC209 is level adjusted and fed out on pin 6 and applied to the RF unit where it modulates the TCXO. The potentiometer is set by the logic during alignment, and is used to balance the VCO and TCXO modulation signals.

4.9 SMARTNET DATA PROCESSING

Both the transmit and receive SMARTNET/ SmartZone data signals are applied to a filter formed by IC112A/B and IC113B. Switching of these signals

is provided by gate IC110 which is controlled by the SN_TR signal from pin 95 of the microprocessor. When this signal is high, the transmit data signal on pin 6 is selected is routed to the filter, and when it is low the receive data signal on pin 7 is routed to the filter.

IC112B, IC112A, and IC113B form a 1800 Hz low-pass filter which attenuates unwanted frequencies above the SMARTNET/SmartZone data band. The output of this filter on U113B, pin 7 is then fed to IC114A/B which provide DC restoration when data is being received. The signal is also fed to gate IC210 in the transmit data circuit to be transmitted when applicable.

The DC restoration circuit formed by IC114A/B and IC113A is similar to the receive data circuit described in Section 4.7.1. It converts the data signal from AC floating at half supply to DC levels of 0 and 5 volts that can be detected by the microprocessor. Diodes D104 and D105 charge and discharge C158 and C157 to establish a DC reference on pin 2 of comparator IC113A that is the average of the positive and negative going alternations. Q106 turns on in the transmit mode which grounds pin 2 and disables this circuit.

In the transmit mode, gate IC210 selects either the SMARTNET data signal or the Call Guard data signal. It is controlled by the same SN_TR signal that controls IC110. The output signal on pin 1 is then applied to potentiometer 1 in IC209. Refer to Section 4.7.2 for more information on this circuit.

November 1999

 

Part No. 001-7780-500

4-10

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Contents 7780 Page Page Table of Contents Table of Contents CONT’D List of Tables List of FiguresGeneral Information Scope of Manual Equipment DescriptionPart Number Breakdown AccessoriesFactory Customer Service Transceiver IdentificationToll-Free 800 AccessoriesAccessory Factory ReturnsDefinitions Replacement PartsInternet Home Intrinsically Safe Information Intrinsically Safe and Nonincendive Ratings Temperature Code T3CPossible Ignition Sources Classification of Hazardous Areas and AtmospheresTypical Hazard Group Class Accessing PC BoardsMaterial Classification Area ClassificationRemoving RF Unit Removing Logic UnitSpecifications GeneralControls and Display FeaturesTransceiver Operation TX Indicator Red Indicates when the transmitter is keyed Low-Battery Indicator AmberDisplay DisplayFront Panel Keys Full Keypad Model General Operation Turning Power on and Setting VolumeOption Switches BacklightSee Option Switch FunctionsFunction Conv Tone ENABLE/DISABLE ScanningConventional and SMARTNET/ Smartzone Operation Monitoring Before Transmitting Conventional FeaturesDisplay Mode Selection Call Guard Squelch Monitor ModeBusy Channel Lockout Power Output Select Penalty TimerConversation Timer Conventional Mode ScanningPriority Channel Sampling DTMF/ANI Signaling Standard Conventional CallsStandard Group Calls SMARTNET/SMARTZONE FeaturesViewing Unit ID Enhanced Private Conversation CallsTransceiver Operation Private Conversation II Calls Telephone Calls Call Alert Sending Status Conditions Emergency Alarm and CallMessaging Dynamic Regrouping Failsoft OperationSMARTNET/SMARTZONE Scanning Supervisory Tones Zone Change Parameter Keypad ProgrammingMenu Description Channel Parameters Channel Change ParameterSystem Parameters Transceiver Programming Programming SetupPctrunk Software Installation Computer DescriptionProgramming File Types Connecting RPI to Computer and TransceiverStarting and Exiting Help FilesFile Size Indication Screen Pop-Up Buttons and File Size IndicatorProgramming Procedure Creating and Displaying SystemsMenu Commands Menu BarSystems Menu Radio Type MenuDownload Menu Upload Menu Window MenuBand DefaultsRADIO-WIDE Parameter Screens ZonesModify List Screen Radio Wide Scan ListRadio-Wide Scan List Screen Assign Function ButtonsFull Spectrum CC Scan RADIO-WIDE Conventional ScreenRADIO-WIDE SMARTNET/SMARTZONE Screen Hot DtmfProgramming Conventional Systems and Channels Adjustable ParametersRADIO-WIDE Portable Options Screen Conventional System General ScreenKeypad Editing TimersConventional System Modify Scan List Screen Scan List ButtonPriority Channel Selection Scan TimersSetting UP Conventional Channels Conventional Channel Screen Parameters Selected ChannelChannel Type Transmit PowerSignaling Tx Time-OutISW Delay Time Restricted AccessTime-Out Timer Splinter ChannelsPhone Interconnect SMARTNET/SMARTZONE System Other ID’S ScreenSMARTNET/SMARTZONE System Phone Interconnect Screen Private CallSMARTNET/SMARTZONE System Talk Groups Screen SMARTNET/SMARTZONE System Emergency Settings ScreenEmergency Alarm Failsoft ChannelMessage Aliasing Screen SMARTNET/SMARTZONE System Lists ScreensTrunking Phone List Screen Announcement Groups Screen Control Channels ScreenTrunking Call List Screen SMARTNET/SMARTZONE Channel Screen Parameters Setting UP SMARTNET/SMART- Zone ChannelsStatus Aliasing Screen SMARTNET/SmartZone Channel Screen Other Screen ParametersCall Guard CTCSS/DCS Codes and Tones Recommended Tone Call Guard Codes FreqMHz Channels MHz Channels MHz Channels MHz Channels MHz Channels MHz Channels Circuit Description Power Switching and RegulationPower Switching Synthesizer DescriptionCharge Pump Q1, Q2, Loop Filter VCO and Tcxo ModulationSynthesizer Chip IC1 If Amplifier Q2, LIMITER/DETECTOR IC3 Receiver Circuit DescriptionRF Amplifier Q1, First Mixer Q2 Transmitter Description Antenna Switch and LOW-PASS FilterSquelch Circuit IC4A/B, IC5A Amplifier Q9, Driver Q8Control Logic and Display Receive Audio ProcessingMicroprocessor IC306 Pin Descriptions Pin Port Name Input or Description Active High OutputHvfulswlrq Receive Data FILTER/DETECTOR IC102A/B, IC107A/B Audio Amplifier IC104-IC106Receive and Transmit Data Processing Transmit Data Filter IC206B/ IC206A Transmit Audio ProcessingLOW-PASS Filter IC205A/B Smartnet Data ProcessingPower Setting Operating Time Battery Pack and Charger InformationBattery Pack Function Fahrenheit CelsiusBattery Pack and Charger Information Alignment Procedure and Performance Tests Test SetupTune Software Hqhudo Mm/3/32 Mm/1/8 Phone JackPreliminary Setup Main Pctune ScreenHigh Power Level = 3.0 watts Low Power Level = 1.0 watt Transmit Frequency and PowerTransmit Power Adjustment Screen Modulation BalanceAudio Deviation Squelch AdjustRssi Adjust Data DeviationPerformance Tests Receiver Performance TestsTransmit Frequency Power OutputTransmitter Performance Tests Transmit ModulationThis page intentionally left blank Chassis Parts Parts ListDisplay Assembly Ref No DescriptionKEY Assembly Display AssemblyIf Assembly If AssemblyKEY Assembly PLL Assembly RF UnitRF Unit NJM2904V-TE1 IC RF Unit Logic Unit Logic Unit TDA7233D IC Logic Unit 200K ERJ3GE MP35 MP18 MP25 KEY Front Panel EP2EP1 MP32 MP33 MP27 MP34 MP28 MP29 MP23 MP22 MP30 MP24 MP26 MP18 PLL Board Bottom View Schematic Diagrams and Component LayoutsPLL Board TOP View If Board TOP View If Board Bottom ViewTransceiver Block Diagram RF UnitRF Board TOP View MICRF Board Schematic If AMPLogic Board TOP View HD1Logic Board Schematic Receive Audio ProcessingDisplay Board Bottom View GND KEYR3 KEYR2 KEYR1 KEYR0 KEYS3 KEYS2 KEYS1 KEYS0 GNDDisplay Board Schematic DS3 DS4 DS5KEY Board Front View KEY Board Back ViewKEY Board Schematic S S R R R RScan HC2 HC7 HC8 HC3 Schematic Diagrams and Component Layouts
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