HP TM 11-6625-2779-14&P manual Detailed Circuit Description, Simplified Dial BAT Function

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HOLD: When the HOLD pushbutton is depressed a high inductance coil LI is connected across the Model 3555B balanced INPUT terminals if the INPUT

Section IV

4-13. The output of the Input Amplifier goes to the INPUT switch where noise filters are set up for selection by the NOISE WTG switch. In the NOISE position, either 3kHz FLAT weighting, C Message weighting, 15kHz FLAT weighting or PROGRAM weighting can be selected by the NOISE WTG switch. In the TMS position of the INPUT switch the filters are bypassed for transmission level measurements.

4-14. The output from the INPUT switch goes to the meter amplifier. This amplifier provides an ac signal to the DIAL/AC MON jacks so that a handset can be used to listen to the signal being measured. This is particularly useful in determining noise characters.

4-15. The detector circuit provides an equivalent rms detected voltage to drive the meter. The meter has shaped pole pieces to provide a linear meter scale both for dBm and dBrn.

4-16. DETAILED CIRCUIT DESCRIPTION.

4-17. The purpose of the function switch is to set up the input conditions to match the type of measurement being made. Impedances can be selected to match the lines to be tested and can be either bridged or terminated. Separate transformers are selected for voice frequency and carrier frequency measurements. A 40dB attenuator is bridged across the input terminals for longitudinal noise measurements when the Ng pushbutton is depressed. The HOLD function places a high inductance holding coil across the input terminals to simulate an off-hook condition. Each of these functions is described in detail in the following paragraphs.

a.

Model 3555B

switch is in the TERM position. A bridging HOLD is not possible. The TERM switch connects the two windings of L1 in series.

b.DIAL BAT: (See Figure 4-2)The DIAL BA1 pushbutton serves two purposes. First it disconnects the meter from the detector and connects it to the unregulated power supply so that the battery voltage can be monitored. Secondly, the DIAL/AC MON jacks are disconnected from the amplifier ac output and connected to the INPUT

jacks. This permits connecting the lineman's handset to the balanced line for the purpose of dialing.

c.Ng: (See Figure 4-3)The Ng pushbutton connects a 40dB attenuator across the balanced input terminals for longitudinal measurements. This attenuator consists of A1R5 thru A1R8 and A1C1. The output is taken from the junction of AIC1 and A1R8. This output is referenced to ground and applied to the voice frequency transformer A1T2.

d.900 (Vf/Nm): The 900 function switch S4 selects terminating resistors AIRI and A1R9 for 900 ohm terminations. The INPUT switch must be in _ the TERM position to complete the circuit for this termination. The 900 function switch also places a ground on the 900 ohm relay A3K1 which provides gain switching in the Input Amplifier so that the meter will indicate in dBm. The 900 ohm signal is applied to the voice frequency transformer A1T2. HOLD can be accomplished on this function.

Figure 4-2. Simplified DIAL BAT Function

4-2

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Contents HEADQUARTERS, Department of the Army Reporting Errors and Recommending Improvements TM 11-6625-2779-14&PTechnical Manual Headquarters Department of the Army NSNReplaceable Parts List of Tables List of IllustrationsIii Section Introduction Maintenance Forms, Records, and ReportsScope Destruction of Army Electronics Materiel Administrative StorageReporting Equipment Improvement Recommendations EIR Items Comprising an Operable Equipment Specifications Voice Frequency Level Measurements 20Hz to 20kHzSection Section General Information IntroductionAccessory Equipment Supplied Accessory Equipment SuppliedInstrument Identification BAL ModificationSection Installation Inspection Warranty ExceptionPower Requirements BatteryInstallation and Removal of Battery Cover RemovalControls Connectors Indicators BatterySection Operating InstructionsFront Panel Controls, Indicators, and Connectors Front, Side and Rear Pane Side Panel Controls and Connectors Level and Noise Measurements Level MeasurementsPage Noise Measurement Recorder Compatibility ApplicationsRecorder Compatibility Chart Identifying Noise Characteristics Transmission Loss MeasurementsCrosstalk Measurements Crosstalk Correction FactorMeasurements in DBC Reinstall the set in its case 0dBmInput jacks are connected in parallel. If a 600 ohm 135 BALStep Procedure Level Measurement Noise Metallic MeasurementsNoise-to-Ground Measurements Balance Measurement Recorder CalibrationExample Transmission Loss MeasurementBlock Diagram Description Section Theory of Operation IntroductionDetailed Circuit Description Simplified Dial BAT FunctionInput Amplifier A3. Schematic No Range Attenuator A2Setting Attenuation FILTERS. Schematic NoRange Attenuator Pads UsedKHz Flat and Program Weighting Curves C-MSG and 1SkHz Flat Weighting Curves Meter AMPLIFIER. Schematic No DETECTOR. Schematic NoPower Supply and Series Regulator Schematic No Section Maintenance Introouction Instrument Recommended Type Required Characteristics ModelFactory Selected Values BAL ConversionPerformance Checks Level Accuracy ChecksFunction CARRIER, 75 Unbal TMS, TermUnbal Carrier Accuracy Check RangeFrequency 30Hz to 1MHz 100Hz to 600kHz 1MHz to 3MHzReturn Loss Check 20Hz to 20kHz 40Hz to 15kHz 100Hz to 20kHz 100Hz to 15kHzReturn Loss Test Set-Up Filter Response Checks Filter Response ChecksMSG dBm 3kHz Flat dBm 15kHz Flat dBm Program dBm Input Balance Bridging LossTMS Brdg Input TMS BrdgAdjustment and Calibration Procedure Power Supply CheckUnbal Calibration Attenuator CalibrationCommon Mode Adjustment Frequency Response AdjustmentBalance Check Troubleshooting Procedures Assembly RemovalFilter Calibration Troubleshooting Tree Front Panel Trouble Analysis Dial BATFront Panel Troubleshooting Function TroubleshootingRange Troubleshooting Front Panel Trouble Analysis ContdTroubleshooting Input Amplifier Filter TroubleshootingTroubleshooting the Meter Amplifier and Detector Defective FunctionFunction Switch Resistance Values Function Input Jacks DIAL/AC MON JacksTip to Ring Tip to Ground Ring to Ground Brdg Term10. Resistance Checks 11. Factory Selected ValuesRange dBm Pin 1 to Pin 2 to Performance Check Test Card Description CheckCarrier 75 Unbal Level Accuracy Check Carrier 135 BAL Level Accuracy CheckPerformance Check Test Card Contd Carrier 600 BAL Level Accuracy CheckReturn Loss Check Filter Response Checks MSGProgram Bridging Loss CheckSection Replaceable Parts Introduction Ordering InformationReplaceable Parts 03555-66507 PC Board Assy functionReplaceable Parts Contd 03555-66508 Board Assy amplifierA3 Contd 03555-66506 PC Board Assy filter A4 Contd Chassis Mounted Components Chassis Mounted Components Contd MiscellaneousMiscellaneous Contd Replacement National Part Stock Number Fscm Part Number National Stock Number Cross Reference IndexFscm National Stock NumberPage Model 3555B Appendix a Code List of Manufacturers Circuit Diagrams Functional Block DiagramSchematic Diagrams Reference DesignationsSection Model 3555B Functional Block Diagram 7-4A1 Function Assembly Schematic and Component Location 7-67-8 A4 Filter Schematic and Component Location 7-1011/7-12 Appendix a ReferencesMaintenance Allocation Section I. Introduction General Maintenance FunctionAppendix B Column EntriesTool and Test Equipment Requiremen ts Sec Remarks SecAudio Level Meter TA-885/U TM 11-7725-2779-14&P REF Code NumberManual Backdating Changes Appendix CTransmission and Noise Measuring SET Delete CR6 across M1 Government Printing Office 1980-603-128/66General, United States Army Chief of StaffMajor General, United States Army Adjutant General Active ArmyPage PIN
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