EFJohnson 764X, 761X service manual UHF Transmitter Circuit, Microphone Amplifier Circuit

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 EFJohnson 764X, 761X service manual RLOý0/ìçíå$ýì5í.ð7 Íëëðêäíçðçèç 03ì Ýìäëëý9&2ýFDVH EFJohnson 761X, 764X service manual 5íéé 5HVý5-ê*-ýìííý9ýõìíýRKPô Íëëðêäíçðìêå 5íéè EFJohnson 764X, 761X service manual 5ìèé 5HVý5-ê*-ýìíéý9ýõìííýNýRKPô EFJohnson 761X, 764X service manual Æçéíýõ8+ôý0$,1ý81,7 EFJohnson 764X, 761X service manual Íêì HUDPLFý&ìçíåý-%ýì+ýìíë.ð7ð$ Íëëðêäíçðíçí Íêë EFJohnson 761X, 764X service manual Íäé HUDPLFý+0çí6-ý&+ýíêíýèíí9ý
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UHF (7640) CIRCUIT DESCRIPTION

Part of the AF signal from pin 9 of FM IF circuit IC1 is applied to pin 24 of level controller IC12. This device allows the CPU to control the squelch threshold level. The level-controlled output signal on pin 23 is applied to IC1, pin 8 which is the input of an internal filter (see Figure 5-4). Noise frequencies are passed and then fed out on pin 7 and also applied to an inter- nal noise detector.

The detected noise signals are rectified and fed out on pin 13 without smoothing. The noise signal (NOIS) is then applied to pin 19 of CPU IC1. The CPU analyzes the noise condition and outputs the RMUT signal via I/O expander IC13. This signal con- trols AF mute switch IC11a (see Figure 5-5).

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 IC7b 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 I/O expander IC13.

5.6 UHF TRANSMITTER CIRCUIT

5.6.1 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 IC8b and limited by IC8a. Pre-emphasis is provided by R152 and C180. The signal is then fed to splatter filter IC7a and then to pin 11 of switching circuit IC11.

The output signal from IC11 on pin 10 is fed to pin 16 of level controller IC12. This device provides deviation control and is also used in the receive mode to provide volume control. The level controlled output on pin 15 is fed to pin 3 of switching circuit IC11. The switched output (MOD) on pin 4 is then applied to the PLL circuit (D21) where it frequency modulates the transmit signal.

Narrow band/wideband switch Q35 is connected to the input of the splatter filter IC7a and switched by the “NWC” signal from the I/O expander IC13. When “NWC” is high, Q35 shifts the filter cut-off frequency for narrow band deviation selection.

5.6.2 MODULATION CIRCUIT

The microphone audio signal modulates the fre- quency of transmit VCO Q25. The “MOD” signal from switch IC11, pin 4 changes the reactance of diode D21 and this modulates the frequency of trans- mit VCO Q25. The modulated VCO signal is ampli- fied by buffer amplifiers Q28 and Q30 and applied to the transmit driver circuit (Q21).

5.6.3 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 Q30 passes through the T/R switch D18 and is ampli- fied by the buffer amplifiers Q21, Q20, and driver Q19. The signal is then applied to the power amplifier module IC5.

5.6.4 POWER AMPLIFIER MODULE

The power amplifier module amplifies the driver signal to the output power level. The RF signal from the driver Q19 is applied to the power module which produces 35 watts of output power at the antenna jack.

The amplified signal is fed through antenna switching circuit D3, a low-pass filter and APC detec- tor, and is then applied to the antenna jack. The collec- tor voltage of driver Q19 and the control voltage on pin 2 of the power module IC5 come from APC tran- sistors Q17 and Q18. Transmit switch Q16 turns off Q17 and Q18 when the transmitter is disabled.

 

November 1998

5B-9

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 75xx Accessories AccessoryToll-Free 800 Factory ReturnsReplacement Parts Internet HomeThis page intentionally left blank VHF and 7640 UHF Mobile Specifications GeneralGeneral Information Installation and Disassembly Transceiver InstallationInstalling Mounting Bracket Installing Microphone HangerPower Cable Installation Cable InstallationPower Cable Fuses Changing 20-Ampere Power Cable FusesUsing AN External Speaker Accessory Cable InstallationRemoving PC Board Transceiver DisassemblyRemove shield E 2-TONE/5-TONE Module Installation Installation ProcedureSetting 5-Tone Deviation 2 2-TONE ProgrammingInstallation and Disassembly Features OperationTransceiver Back Panel Controls and DisplayBasic Operation Direct Selection The F1-F4 Receiving and Placing Calls TIME-OUT Timer Programmable FunctionsOption Key Programmable Functions Function Key Label Description Section NoMonitor Mode Select Output Power SelectCall Guard Tone Select Channel SelectChannel Scan Priority Channel Sampling Programming Setup Section ProgrammingProgramming Cables Programming SoftwareStarting the Program Special Keys and FunctionsMenu Flow File MenuScreen Menu Program MenuPrint Menu Model MenuMemory Channel Screen Description LMR Models Setup MenuParameter Description Bank Select Timer Ch AtrFrequency Rx/TxAuto Reset LockoutScan ToneKey and Display Assign Screen Description Key DescriptionKey Description Label RF Power Dtmf Autodial Screen DescriptionSelection Bank/FreeScan Function Screen Description Continuous Tone Screen DescriptionParameter Description Stop Timer 2-Tone Code Channel Screen DescriptionResume Auto CHEXO Timer Timer Auto TxAuto 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 CircuitPower Amplifier Module VHF Transmitter CircuitMicrophone Amplifier Circuit Modulation CircuitVHF PLL Circuit APC CircuitPLL Circuit Line Description VHF IC PIN DescriptionsPin Port Description VHF I/O Expander IC5 Main Unit PinVHF Port Expander IC11 Main Unit 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 UnitAdjustment Procedure Test SetupSuggested Test Equipment Equipment Grade and RangeTest Channels Test CableVHF Test Frequencies COMPUTER-AIDED TuningUHF Test Frequencies VHF Adjustments VHF AdjustmentsPreliminary Setup PLL Adjustment VHF ModelsOutput Power Adjust VHF Adjustments CONT’DFM Deviation Adjust Dtcs Waveform Adjust Receiver Adjustments VHF ModelsBandpass Filter Adjust 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 Schematic Diagrams and Component Layouts VHF 7610 Block DiagramMain Unit 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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