EFJohnson 761X, 764X service manual PLL Circuit UHF, UHF PLL Circuit

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UHF (7640) CIRCUIT DESCRIPTION

Figure 5-6 PLL Circuit (UHF)

5.6.5 APC CIRCUIT

The APC (Automatic Power Control) circuit pro- tects the power amplifier from damage caused by a mismatched antenna load, and provides a stable power output.

One diode in D1 detects forward signals and the other detects reverse signals. The combined voltage is at minimum level when a matched antenna load of 50 ohms is present and then increases as it becomes mis- matched. The detected voltage is applied to pin 6 of inverse amplifier IC4b. Power setting voltage T4 is applied to the other input (pin 5) as a reference.

When antenna impedance is mismatched, the detected voltage exceeds the power setting voltage. The output voltage on pin 7 then decreases which turns Q17 off slightly. Transistor Q18 then turns off slightly and lowers the voltage applied to the collec- tor of Q19 and the power control input of IC5. This reduces the output power produced by these devices.

5.7 UHF PLL CIRCUIT

5.7.1 PLL CIRCUIT

The PLL (Phase-Locked-Loop) circuit provides a stable (± 2.5 PPM) receive first injection and transmit frequency. The PLL circuit consists of PLL circuit IC2, a loop filter, and reference oscillator. A block diagram of the PLL circuit is shown in Figure 5-6.

The signal from VCOs (Voltage-Controlled

Oscillator) Q23 and Q25 is buffered by Q28 and Q29 and then applied to pin 2 of IC10. The prescaler in IC10 divides the VCO signal down so that it is within the frequency range of the programmable counter.

A reference frequency generated by reference oscillator X2 is applied to pin 15 of IC1. This signal is divided down by a programmable divider and pro- vides the reference input to the phase detector. When the VCO is oscillating at the correct frequency, the VCO-derived input to the phase detector is the same frequency as the reference input.

November 1998

 

Part No. 001-7600-001

5B-10

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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 Accessory 75xx AccessoriesToll-Free 800 Factory ReturnsInternet Home Replacement PartsThis page intentionally left blank General VHF and 7640 UHF Mobile SpecificationsGeneral Information Transceiver Installation Installation and DisassemblyInstalling Microphone Hanger Installing Mounting BracketPower Cable Installation Cable InstallationChanging 20-Ampere Power Cable Fuses Power Cable FusesUsing AN External Speaker Accessory Cable InstallationRemove shield E Transceiver DisassemblyRemoving PC Board Installation Procedure 2-TONE/5-TONE Module InstallationSetting 5-Tone Deviation 2 2-TONE ProgrammingInstallation and Disassembly Operation FeaturesBasic Operation Controls and DisplayTransceiver Back Panel Direct Selection The F1-F4 Receiving and Placing Calls Programmable Functions TIME-OUT TimerOption Key Programmable Functions Function Key Label Description Section NoOutput Power Select Monitor Mode SelectCall Guard Tone Select Channel SelectChannel Scan Priority Channel Sampling Section Programming Programming SetupProgramming Cables Programming SoftwareSpecial Keys and Functions Starting the ProgramMenu Flow File MenuProgram Menu Screen MenuPrint Menu Model MenuParameter Description Bank Select Setup MenuMemory Channel Screen Description LMR Models Ch Atr TimerFrequency Rx/TxLockout Auto ResetScan ToneKey Description Key and Display Assign Screen DescriptionKey Description Label Dtmf Autodial Screen Description RF PowerSelection Bank/FreeParameter Description Continuous Tone Screen DescriptionScan Function Screen Description 2-Tone Code Channel Screen Description Stop TimerResume Auto CHTimer Auto Tx EXO TimerAuto Tx StunCommon Screen Description Expert Screen Description Unique PMR Screens Unique PMR European ScreensCloning Programming ONE Transceiver with Another Memory Channel Screen PMR Models This page intentionally left blank VHF Receiver Circuit VHF 7610 Circuit DescriptionReceiver Mute Circuit Audio Amplifier CircuitVHF Transmitter Circuit Power Amplifier ModuleMicrophone Amplifier Circuit Modulation CircuitPLL Circuit APC CircuitVHF PLL Circuit Pin Port Description VHF IC PIN DescriptionsLine Description Pin VHF I/O Expander IC5 Main UnitVHF Port Expander IC11 Main Unit Pin Port Description NameUHF Receiver Circuit UHF 7640 Circuit DescriptionSecond if System IC1 UHF UHF Transmitter Circuit UHF PLL Circuit PLL Circuit UHFUHF CPU IC1 Port Allocation UHF Power SupplyUHF Port Expander IC13 Main Unit UHF I/O Expander IC12 Main UnitTest Setup Adjustment ProcedureSuggested Test Equipment Equipment Grade and RangeTest Cable Test ChannelsUHF Test Frequencies COMPUTER-AIDED TuningVHF Test Frequencies VHF Adjustments VHF AdjustmentsPreliminary Setup PLL Adjustment VHF ModelsFM Deviation Adjust VHF Adjustments CONT’DOutput Power Adjust Receiver Adjustments VHF Models Dtcs Waveform AdjustBandpass Filter Adjust Squelch AdjustBeep Tone Level Beep Tone Level AdjustmentTransmitter Adjustments UHF Models UHF AdjustmentsPLL Adjustment UHF Models UHF Adjustment Points UHF Adjustments CONT’DUHF Adjustments CONT’D Receiver Adjustments UHF Models Æçìíýõ9+ôý0$,1ý81,7 Parts ListÍäç HUDPLFý&ìçíåý-%ýì+ýìíë.ð7ð$ 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 Front Unit VHF 7610 Exploded ViewUHF 7640 Exploded View VHF 7610 Block Diagram Schematic Diagrams and Component LayoutsMain Unit Front UnitVHF 7610 Transistor Basing Diagrams Foldout → VHF 7610 Main Board TOP View VHF Main Unit VHF 7610 Main Board SchematicUHF 7640 Block Diagram UHF 7640 Main Board Bottom View J4 T o O p tion al Un it UHF 7640 Main Board TOP ViewUHF 7640 Main Board Schematic VHF/UHF Front Unit Board Bottom View VHF/UHF Front Unit Board TOP ViewVHF/UHF Front Unit Schematic UHF 7640 Transistor Basing Diagrams