EFJohnson 764X, 761X VHF Transmitter Circuit, Microphone Amplifier Circuit, Modulation Circuit

EFJohnson 764X, 761X service manual Dtmf Autodial Screen Description, RF Power, Selection, Bank/Free, Opening EFJohnson 761X, 764X Continuous Tone Screen Description, Scan Function Screen Description, Parameter Description EFJohnson 764X, 761X service manual Tone Code Channel Screen Description, Stop Timer, Resume, Auto CH EFJohnson 761X, 764X Stun, Rx Code Common Screen, Notone, Group, EXO Timer, Beep Repeat, Timer Auto Tx, Tx Code Screen EFJohnson 764X, 761X service manual Common Screen Description EFJohnson 761X, 764X service manual Expert Screen Description EFJohnson 764X, 761X service manual Unique PMR European Screens, Unique PMR Screens EFJohnson 761X, 764X service manual Cloning Programming ONE Transceiver with Another EFJohnson 764X, 761X service manual Memory Channel Screen PMR Models EFJohnson 761X, 764X service manual This page intentionally left blank EFJohnson 764X, 761X service manual VHF 7610 Circuit Description, VHF Receiver Circuit EFJohnson 761X, 764X service manual Audio Amplifier Circuit, Receiver Mute Circuit EFJohnson 764X, 761X VHF Transmitter Circuit, Microphone Amplifier Circuit, Modulation Circuit, Transmit Driver Circuit EFJohnson 761X, 764X service manual APC Circuit, VHF PLL Circuit EFJohnson 764X, 761X service manual VHF IC PIN Descriptions, Line Description, Pin Port Description EFJohnson 761X, 764X VHF I/O Expander IC5 Main Unit, VHF Port Expander IC11 Main Unit, Pin Port Description Name EFJohnson 764X, 761X service manual UHF 7640 Circuit Description, UHF Receiver Circuit EFJohnson 761X, 764X service manual Second if System IC1 UHF EFJohnson 764X, 761X service manual UHF Transmitter Circuit, Microphone Amplifier Circuit EFJohnson 761X, 764X service manual PLL Circuit UHF, UHF PLL Circuit EFJohnson 764X, 761X service manual UHF Power Supply, UHF CPU IC1 Port Allocation EFJohnson 761X, 764X service manual UHF I/O Expander IC12 Main Unit, UHF Port Expander IC13 Main Unit EFJohnson 764X, 761X service manual Adjustment Procedure, Test Setup, Suggested Test Equipment, Equipment Grade and Range EFJohnson 761X, 764X service manual Test Channels, Test Cable EFJohnson 764X, 761X service manual VHF Test Frequencies, UHF Test Frequencies, COMPUTER-AIDED Tuning EFJohnson 761X, 764X VHF Adjustments, Preliminary Setup, PLL Adjustment VHF Models, Transmitter Adjustments VHF Models EFJohnson 764X, 761X service manual VHF Adjustments CONT’D, Output Power Adjust, FM Deviation Adjust EFJohnson 761X, 764X Dtcs Waveform Adjust, Receiver Adjustments VHF Models, Bandpass Filter Adjust, Squelch Adjust EFJohnson 764X, 761X service manual Beep Tone Level Adjustment EFJohnson 761X, 764X service manual UHF Adjustments, PLL Adjustment UHF Models, Transmitter Adjustments UHF Models EFJohnson 764X, 761X service manual UHF Adjustments CONT’D, UHF Adjustment Points EFJohnson 761X, 764X service manual UHF Adjustments CONT’D Receiver Adjustments UHF Models, Bandpass Filter Adjust EFJohnson 764X, 761X service manual Parts List, Æçìíýõ9+ôý0$,1ý81,7 EFJohnson 761X, 764X service manual Íäç HUDPLFý&ìçíåý-%ýì+ýìíë.ð7ð$ Íëëðêäíçðíçí Íäæ EFJohnson 764X, 761X service manual Ìää HUDPLFý&ìçíåý-%ýì&ýìíé.7ð1 Íëëðêäíçðçìé Ëíí EFJohnson 761X, 764X service manual Ëäí HUDPLFý&ìçíåý-%ýìýìíê.ð7ð$ Íëëðêäíçðíçê Ëäì
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VHF (7610) CIRCUIT DESCRIPTION

Part of the AF signal from pin 9 of FM IF circuit IC3 is applied to pin 24 of level controller IC5. This device allows the CPU to control the squelch threshold level. The level-controlled output signal on pin 23 is applied to IC3, pin 8 which is the input of an internal filter (see Figure 5-1). Noise frequencies of about 10 kHz are passed and then fed out on pin 7 and also applied to an internal noise detector.

The detected noise signal is rectified and fed out on pin 13 without smoothing. The noise signal (NOIS) is then applied to pin 19 of CPU IC1. The CPU ana- lyzes the noise condition and outputs the RMUT sig- nal via I/O expander IC11. This signal controls AF mute switches IC4a and c (see Figure 5-2).

Call Guard (CTCSS/DTCS) Operation

The tone Call Guard squelch circuit detects AF signals and opens the squelch only when receiving a signal containing a matching subaudible tone or code (CTCSS or DTCS). When tone squelch is in use and a signal with a mismatched or no subaudible tone is received, the tone squelch circuit mutes the AF signals even when noise squelch is open.

A portion of the audio signal from amplifier IC7a passes through low-pass filter Q5 in the front unit to remove voice signals. It is then applied to CPU IC1 on pin 97 via the “CTCIN” line. The CPU detects the CTCSS or DTCS signaling and controls the AF mute switch via I/O expander IC11.

5.2 VHF TRANSMITTER CIRCUIT

5.2.1 MICROPHONE AMPLIFIER CIRCUIT

The microphone amplifier circuit amplifies the microphone audio signal to the level required by the modulation circuit and also provides pre-emphasis.

The microphone audio signal is amplified by IC7d, with R172 and C295 on the output providing pre-emphasis. The microphone audio signal is then fed to switch IC4 on pin 4 and the switched output signal is on pin 3. This signal is then applied to high-pass fil- ter IC8a/b which attenuates frequencies in the Call Guard (CTCSS/DTCS) range. This is the same filter used for receive audio filtering.

The signal is then fed to IC7b and IC7c which provide buffering and amplification. Deviation limit- ing is then provided by level controller IC5. The input to this device is pin 16 and the output is pin 15. The signal is then fed to splatter filter IC6b and switch IC4. The input is on pin 11 and the output is on pin 10. The modulation signal is then applied to the PLL circuit as “MOD”.

Narrow band/wideband switch Q21 is connected to the input of the splatter filter IC6b and switched by the “NWC” signal from the I/O expander IC11. When “NWC” is high, Q21 shifts the filter cut-off frequency for narrow band deviation selection.

5.2.2 MODULATION CIRCUIT

The microphone audio signal modulates the fre- quency of VCO Q7/Q8. The “MOD” signal from switch IC4, pin 10 changes the reactance of diode D9 which frequency modulates the VCO frequency. The modulated VCO signal is amplified by buffer amplifi- ers Q6, Q5, and Q4 and applied to the transmit driver circuit.

5.2.3 TRANSMIT DRIVER CIRCUIT

The transmit driver circuit amplifies the VCO oscillating signal to the level required by the power amplifier module. The RF signal from buffer amplifier Q4 passes through the T/R switch D5 and is amplified by the buffer-amplifiers Q3 and Q2 and driver Q1. The signal is then applied to the power amplifier module IC1.

5.2.4 POWER AMPLIFIER MODULE

The power amplifier module amplifies the driver signal to the output power level. The RF signal from the driver Q1 is applied to the power module which produces 45 watts of output power at the antenna jack.

The amplified signal is fed through antenna switching circuit D3 and D4, a low-pass filter and APC detector, and is then applied to the antenna jack. The collector voltage of driver Q1 and the control voltage on pin 2 of the power module IC1 come from APC transistors Q17 and Q18. Transmit switch Q23 turns off Q17 and Q18 when the transmitter is disabled.

 

November 1998

5A-3

Part No. 001-7600-001

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Contents 761x VHF 764x UHF Conventional Mobile Conventional FM TWO-WAY Radio Table of Contents Table of Contents CONT’D Schematic Diagrams and Component Layouts General Information Toll-Free 800 75xx AccessoriesAccessory Factory ReturnsReplacement Parts Internet HomeThis page intentionally left blank VHF and 7640 UHF Mobile Specifications GeneralGeneral Information Installation and Disassembly Transceiver InstallationPower Cable Installation Installing Mounting BracketInstalling Microphone Hanger Cable InstallationUsing AN External Speaker Power Cable FusesChanging 20-Ampere Power Cable Fuses Accessory Cable InstallationRemoving PC Board Transceiver DisassemblyRemove shield E Setting 5-Tone Deviation 2-TONE/5-TONE Module InstallationInstallation Procedure 2 2-TONE ProgrammingInstallation and Disassembly Features OperationTransceiver Back Panel Controls and DisplayBasic Operation Direct Selection The F1-F4 Receiving and Placing Calls Option Key Programmable Functions TIME-OUT TimerProgrammable Functions Function Key Label Description Section NoCall Guard Tone Select Monitor Mode SelectOutput Power Select Channel SelectChannel Scan Priority Channel Sampling Programming Cables Programming SetupSection Programming Programming SoftwareMenu Flow Starting the ProgramSpecial Keys and Functions File MenuPrint Menu Screen MenuProgram Menu Model MenuMemory Channel Screen Description LMR Models Setup MenuParameter Description Bank Select Frequency TimerCh Atr Rx/TxScan Auto ResetLockout ToneKey and Display Assign Screen Description Key DescriptionKey Description Label Selection RF PowerDtmf Autodial Screen Description Bank/FreeScan Function Screen Description Continuous Tone Screen DescriptionParameter Description Resume Stop Timer2-Tone Code Channel Screen Description Auto CHAuto Tx EXO TimerTimer Auto Tx StunCommon Screen Description Expert Screen Description Unique PMR European Screens Unique PMR ScreensCloning Programming ONE Transceiver with Another Memory Channel Screen PMR Models This page intentionally left blank VHF 7610 Circuit Description VHF Receiver CircuitAudio Amplifier Circuit Receiver Mute CircuitMicrophone Amplifier Circuit Power Amplifier ModuleVHF Transmitter Circuit Modulation CircuitVHF PLL Circuit APC CircuitPLL Circuit Line Description VHF IC PIN DescriptionsPin Port Description VHF Port Expander IC11 Main Unit VHF I/O Expander IC5 Main UnitPin Pin Port Description NameUHF 7640 Circuit Description UHF Receiver CircuitSecond if System IC1 UHF UHF Transmitter Circuit PLL Circuit UHF UHF PLL CircuitUHF Power Supply UHF CPU IC1 Port AllocationUHF I/O Expander IC12 Main Unit UHF Port Expander IC13 Main UnitSuggested Test Equipment Adjustment ProcedureTest Setup Equipment Grade and RangeTest Channels Test CableVHF Test Frequencies COMPUTER-AIDED TuningUHF Test Frequencies Preliminary Setup VHF AdjustmentsVHF Adjustments PLL Adjustment VHF ModelsOutput Power Adjust VHF Adjustments CONT’DFM Deviation Adjust Bandpass Filter Adjust Dtcs Waveform AdjustReceiver Adjustments VHF Models Squelch AdjustBeep Tone Level Adjustment Beep Tone LevelPLL Adjustment UHF Models UHF AdjustmentsTransmitter Adjustments UHF Models UHF Adjustments CONT’D UHF Adjustment PointsUHF Adjustments CONT’D Receiver Adjustments UHF Models Parts List Æçìíýõ9+ôý0$,1ý81,7Íäç HUDPLFý&ìçíåý-%ýì+ýìíë.ð7ð$ Íëëðêäíçðíçí Íäæ Ìää HUDPLFý&ìçíåý-%ýì&ýìíé.7ð1 Íëëðêäíçðçìé Ëíí Ëäí HUDPLFý&ìçíåý-%ýìýìíê.ð7ð$ Íëëðêäíçðíçê Ëäì RLOý0/ìçíå$ýì5í.ð7 Íëëðêäíçðçèç 03ì Ýìäëëý9&2ýFDVH 5íéé 5HVý5-ê*-ýìííý9ýõìíýRKPô Íëëðêäíçðìêå 5íéè 5ìèé 5HVý5-ê*-ýìíéý9ýõìííýNýRKPô Æçéíýõ8+ôý0$,1ý81,7 Íêì HUDPLFý&ìçíåý-%ýì+ýìíë.ð7ð$ Íëëðêäíçðíçí Íêë Íäé HUDPLFý+0çí6-ý&+ýíêíýèíí9ý Õéäíðèìëý0+ô Ìèì 5HIý1Rï Êëç Íëëðêäíçðäèë 4éì 7UDQVLVWRUý7&êçê.ý7ìéæ 5íæé 5ìçå 5HVý5-ê*-ýìíéý9ýõìííýNýRKPô 5217ý81,7 Õ9+ý$1ý8+ý02/6ô =HQHUý0$åíèìð0ýõ7ô Æçìíýõ9+ôý&+$66,6ý3$576 VHF 7610 Exploded View Front UnitUHF 7640 Exploded View Main Unit Schematic Diagrams and Component LayoutsVHF 7610 Block Diagram Front UnitVHF 7610 Transistor Basing Diagrams Foldout → VHF 7610 Main Board TOP View VHF 7610 Main Board Schematic VHF Main UnitUHF 7640 Block Diagram UHF 7640 Main Board Bottom View UHF 7640 Main Board TOP View J4 T o O p tion al Un itUHF 7640 Main Board Schematic VHF/UHF Front Unit Board TOP View VHF/UHF Front Unit Board Bottom ViewVHF/UHF Front Unit Schematic UHF 7640 Transistor Basing Diagrams
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