HP TM 11-6625-2779-14&P Frequency Response Adjustment, Common Mode Adjustment, Balance Check

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Model 3555B

c.Adjust A3R15 for 0dBm indication on the 3555B meter.

d.Change the 654A frequency to 1kHz. Change the 3555B FUNCTION switch to VF/Nm, 600 BAL. Compare the 3555B meter indication with the indication in step c. If any difference exists, adjust A3R15 to split the difference between these two indications.

NOTE

If the set is being operated from the ac line ground currents may be encountered on the low ranges, particularly if other instruments are connected in any way to the 3555B. In order to eliminate this problem, operate the set from its own internal battery or use the C MSG filter. If the C MSG filter is used, perform the filter calibration described in Paragraph 5-24and then perform the following step.

e.Change the 654A to -80dBm output .level at 1.00kHz. Change the 3555B RANGE switch to -80dBm. Adjust A3R26 for 0dBm indication on the 3555B meter.

f.Change the 654A to 135 BAL (150 BAL) and change the 3555B FUNCTION to 135 BAL (I50 BAL). Adjust A3R24 for 0dBm indication on the 3555B meter.

g.Change the 3555B RANGE switch to - 5OdBm, INPUT switch to TMS TERM, and the FUNCTION switch to VF/Nm 600 BAL. Change the 654A to 1kHz at an output level of -50dBm, 600 BAL. Adjust the AMPLITUDE control for exactly 0dBm indication on the 3555B meter.

h.Change the 3555B FUNCTION switch to 900 BAL without changing anything else. Adjust A3R20 for -0.15dBm indication on the 3555B meter.

5-21. FREQUENCY RESPONSE ADJUSTMENT.

a. The following adjustment consists of selecting fixed values for frequency compensation at 20Hz, 600 BAL, -70dBm and 20kHz, 600 BAL, -70dBm.

b.Connect the 654A 600 BAL output to the 3555B input. Set the 3555B controls as follows:

FUNCTION ............... VF/Nm 900 BAL INPUT............................. TMS, TERM RANGE ..................................... 0dBm

Section V

RESPONSE ............................. DAMP

c.Set the 654A (600 BAL) output level to 0dBm at a frequency of 20Hz. The 3555B meter should Section V indicate -0.1SdBm +0.3dBm. Note this indication.

d.Change the 654A output level to -70dBm at a frequency of 20Hz. Change the 3555B RANGE switch to -70dBm and change the FUNCTION to VF/Nm 600 BAL. The 3555B meter should indicate 0dBm +0.3dBm. Note the exact indication.

e.Compensation should be made between the 900 BAL, 0dBm check (step c) and the 600 BAL, -70dBm check (step d). To raise the level, increase the value of A3R72 until the 900 BAL 0dBm check indicates high by the same amount that the 600 BAL, - 70dBm check indicates low. The total difference should not exceed +0.3dBm.

5-22. COMMON MODE ADJUSTMENT.

a.Connect the equipment as shown in Figure

5-5and set the 3555B controls as follows: FUNCTION ................VF/Nm, 600 BAL INPUT...............................TMS, TERM RANGE ....................................... 0dBm

b.Set the 654A frequency to 20kHz and adjust the output level of the 654A for 0dBm indication on the 3555B meter.

c.Disconnect the left output terminal on the 654A and short the tip and ring together on the cable. Down range the 3555B RANGE switch for an on-scale indication.

d.Adjust A1C7 for minimum indication on the 3555B meter. This indication must be down at least 60 dB.

e.Change the 3555B FUNCTION switch to CARRIER, 600 BAL and change the 654A frequency to 100kHz.

f.Use the procedure described above and adjust A1C4 for minimum indication on the 3555B meter. This indication must be down at least 40dB.

5-23. BALANCE CHECK.

a.First check the balance as described in paragraph 5-13to be sure that the balance does not meet specifications. If it does, disregard this step. If it does not perform the following procedure.

b.Since there are no adjustments for balance it will be necessary to change the value of a fixed factory selected capacitor. To adjust the balance on the

5-9

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Contents HEADQUARTERS, Department of the Army NSN Reporting Errors and Recommending ImprovementsTM 11-6625-2779-14&P Technical Manual Headquarters Department of the ArmyReplaceable 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 Voice Frequency Level Measurements 20Hz to 20kHz SpecificationsSection General Information Introduction SectionBAL Modification Accessory Equipment SuppliedAccessory Equipment Supplied Instrument IdentificationBattery Section Installation InspectionWarranty Exception Power RequirementsCover Removal Installation and Removal of BatteryOperating Instructions Controls Connectors IndicatorsBattery SectionFront Panel Controls, Indicators, and Connectors Front, Side and Rear Pane Side Panel Controls and Connectors Level Measurements Level and Noise MeasurementsPage Noise Measurement Applications Recorder CompatibilityRecorder Compatibility Chart Crosstalk Correction Factor Identifying Noise CharacteristicsTransmission Loss Measurements Crosstalk MeasurementsMeasurements in DBC 135 BAL Reinstall the set in its case0dBm Input jacks are connected in parallel. If a 600 ohmLevel Measurement Noise Metallic Measurements Step ProcedureTransmission Loss Measurement Noise-to-Ground Measurements Balance MeasurementRecorder Calibration ExampleSection Theory of Operation Introduction Block Diagram DescriptionSimplified Dial BAT Function Detailed Circuit DescriptionRange Attenuator A2 Input Amplifier A3. Schematic NoPads Used Setting AttenuationFILTERS. Schematic No Range AttenuatorKHz Flat and Program Weighting Curves C-MSG and 1SkHz Flat Weighting Curves DETECTOR. Schematic No Meter AMPLIFIER. Schematic NoPower Supply and Series Regulator Schematic No BAL Conversion Section Maintenance IntroouctionInstrument Recommended Type Required Characteristics Model Factory Selected ValuesTMS, Term Performance ChecksLevel Accuracy Checks Function CARRIER, 75 Unbal30Hz to 1MHz 100Hz to 600kHz 1MHz to 3MHz Unbal Carrier Accuracy CheckRange Frequency20Hz to 20kHz 40Hz to 15kHz 100Hz to 20kHz 100Hz to 15kHz Return Loss CheckReturn Loss Test Set-Up Filter Response Checks Filter Response Checks MSG dBm 3kHz Flat dBm 15kHz Flat dBm Program dBm Input TMS Brdg Input BalanceBridging Loss TMS BrdgAttenuator Calibration Adjustment and Calibration ProcedurePower Supply Check Unbal CalibrationCommon Mode Adjustment Frequency Response AdjustmentBalance Check Troubleshooting Procedures Assembly RemovalFilter Calibration Troubleshooting Tree Dial BAT Front Panel Trouble AnalysisFront Panel Trouble Analysis Contd Front Panel TroubleshootingFunction Troubleshooting Range TroubleshootingDefective Function Troubleshooting Input AmplifierFilter Troubleshooting Troubleshooting the Meter Amplifier and DetectorBrdg Term Function Switch Resistance ValuesFunction Input Jacks DIAL/AC MON Jacks Tip to Ring Tip to Ground Ring to Ground10. Resistance Checks 11. Factory Selected ValuesRange dBm Pin 1 to Pin 2 to Carrier 135 BAL Level Accuracy Check Performance Check Test CardDescription Check Carrier 75 Unbal Level Accuracy CheckCarrier 600 BAL Level Accuracy Check Performance Check Test Card ContdBridging Loss Check Return Loss CheckFilter Response Checks MSG ProgramOrdering Information Section Replaceable Parts Introduction03555-66507 PC Board Assy function Replaceable Parts03555-66508 Board Assy amplifier Replaceable Parts ContdA3 Contd 03555-66506 PC Board Assy filter A4 Contd Chassis Mounted Components Miscellaneous Chassis Mounted Components ContdMiscellaneous Contd National Stock Number Replacement National Part Stock Number FscmPart Number National Stock Number Cross Reference Index FscmPage Model 3555B Appendix a Code List of Manufacturers Reference Designations Circuit DiagramsFunctional Block Diagram Schematic DiagramsSection Model 3555B 7-4 Functional Block Diagram7-6 A1 Function Assembly Schematic and Component Location7-8 7-10 A4 Filter Schematic and Component Location11/7-12 References Appendix aColumn Entries Maintenance Allocation Section I. Introduction GeneralMaintenance Function Appendix BRemarks Sec Tool and Test Equipment Requiremen ts SecAudio Level Meter TA-885/U REF Code Number TM 11-7725-2779-14&PManual Backdating Changes Appendix CTransmission and Noise Measuring SET Government Printing Office 1980-603-128/66 Delete CR6 across M1Active Army General, United States ArmyChief of Staff Major General, United States Army Adjutant GeneralPage PIN
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