EFJohnson 761X, 764X service manual Priority Channel Sampling

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OPERATION

The scan lists are user programmable if the TAG key is available. Pressing this key changes the

status of the displayed channel in the current scan list only. The display indicates “SC ON” if the channel was just added to the scan list and “SC OF” if it was just deleted. In addition, the scan list status is indicated by the decimal point in the display. This indicator is on when the displayed channel is scanned. The decimal point flashes when scanning is occurring.

The scan list status of a channel can be changed while scanning only when listening to a message on the channel. The current status of all the lists is stored in memory. Therefore, the status of the various scan lists does not change when power is turned off.

3.6.3 PRIORITY CHANNEL SAMPLING

Priority channel sampling ensures that messages on priority channels are not missed while listening to

messages on other channels. If priority sampling is used, a priority A channel is designated by program- ming. If the PRI A key is available, pressing that key selects the priority A channel. This key also may be programmed so that if it is pressed and held, the prior- ity A channel changes to the current channel.

Sampling of the priority A channel occurs only when scanning is enabled. It does not occur while transmitting. When the priority channel is sampled while listening to a message on another channel, a series of “ticks” are heard. These ticks are brief inter- ruptions of the audio signal that occur while the trans- ceiver changes channels to check the priority channel.

Another priority channel also can be programmed that can be quickly selected by the PRI B key. This channel is programmed only to allow quick selection and is not sampled while listening to a non-priority channel.

November 1998

 

Part No. 001-7600-001

3-8

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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 InstallationRemoving PC Board Transceiver DisassemblyRemove shield E Installation Procedure 2-TONE/5-TONE Module InstallationSetting 5-Tone Deviation 2 2-TONE ProgrammingInstallation and Disassembly Operation FeaturesTransceiver Back Panel Controls and DisplayBasic Operation 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 MenuMemory Channel Screen Description LMR Models Setup MenuParameter Description Bank Select Ch Atr TimerFrequency Rx/TxLockout Auto ResetScan ToneKey Description Key and Display Assign Screen DescriptionKey Description Label Dtmf Autodial Screen Description RF PowerSelection Bank/FreeScan Function Screen Description Continuous Tone Screen DescriptionParameter 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 CircuitVHF PLL Circuit APC CircuitPLL Circuit Line Description VHF IC PIN DescriptionsPin Port 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 ChannelsVHF Test Frequencies COMPUTER-AIDED TuningUHF Test Frequencies VHF Adjustments VHF AdjustmentsPreliminary Setup PLL Adjustment VHF ModelsOutput Power Adjust VHF Adjustments CONT’DFM Deviation Adjust Receiver Adjustments VHF Models Dtcs Waveform AdjustBandpass Filter Adjust Squelch AdjustBeep Tone Level Beep Tone Level AdjustmentPLL Adjustment UHF Models UHF AdjustmentsTransmitter Adjustments 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