HP TM 11-6625-2779-14&P Noise-to-Ground Measurements Balance Measurement, Recorder Calibration

Page 26

Section III

Model 3555B

Table 3-5. Noise-to-Ground Measurements

Table 3-6. Balance Measurement

STEP

PROCEDURE

1.Turn the 3555B POWER switch to ON and depress the DIAL/BAT pushbutton. The meter should indicate in the green BAT GOOD area. If it does not replace the battery or check the power source. The battery test operates for internal battery, office battery or ac power source.

2.Set the INPUT switch to NOISE BRDG.

3.Select the appropriate weighting filter using the NOISE WTG switch.

4.Set the RANGE switch to 110dBrn.

5.Depress the NG pushbutton and connect the set to the circuit to be tested. Down range for an on-scale indication.

NOTE

Dial and talk may be accomplished on the metallic circuit and the connection held by depressing the HOLD pushbutton.

Table 3-7. Recorder Calibration

STEP

PROCEDURE

1.Determine the input impedance and full scale sensitivity of your recorder and refer to paragraph 3-41and Figure 3-4to determine if your recorder is suitable for use with this set. The dc voltage supplied by the DC MON 310 jack will drive a dc potentiometric recorder requiring 1V or a dc galvanometric recorder requiring 500uA.

2.Connect an input voltage to the set and adjust the RANGE switch until a near full-scale indication is observed on the meter.

3.Connect the recorder plug with the tip negative, to the DC MON jack and adjust the input level until the meter indicates 0dBm. Mark this point on the recorder paper which should be near full scale.

4.Decrease the input level to the set until the' meter indicates -1dBm. Mark this point on the recorder paper. Continue this procedure until every major dBm division on the meter has been calibrated on the recorder paper.

5.The actual level to the set as indicated on the recorder is equal to the algebraic sum of the RANGE setting and recorder indication.

STEP

PROCEDURE

1.Perform the Noise-to-ground measurement as described in Table 3-5.

2.Perform the Noise Metallic measurements as described in Table 3-4.

3.Compute the line balance in dB using the results of the above checks.

Balance (dB) = Nm - NG

EXAMPLE:

 

 

Noise-to-ground

=

+26dBrn

Noise Metallic

=

(-)+90dBrn

Balance in dB

=

-64dBm

NOTE

The noise-to-ground measurement above includes the 40dB correction factor.

Table 3-8. Transmission Loss Measurement

STEP

PROCEDURE

 

 

1.

For a transmission loss measurement to be

 

meaningful, it should first be determined if

 

there are any extraneous signals present that

 

will affect your measurement. To do this,

 

connect the measuring set to the circuit and

 

determine if interfering signals are present.

 

Levels below 60dB can, in most cases, be

 

ignored. A butt-in can be connected to the AC

 

MON jacks to aid in determining the

 

interfering source.

 

 

2.

Establish a connection like the ones shown in

 

Figure 3-6.

 

 

3.

Adjust the oscillator output level for 0dBm.

 

Measure the level at the receiving end and

 

record this level.

 

 

4.

Insertion loss is equal to the difference

 

between the sending level and the receiving

 

level, ignoring any extraneous signals.

 

EXAMPLE:

 

 

 

Sending level

=

0dBm

 

Receiving level =

(-)- 20dBm

 

Insertion loss

=

20dB

 

 

 

 

3-14

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Contents HEADQUARTERS, Department of the Army Technical Manual Headquarters Department of the Army Reporting Errors and Recommending ImprovementsTM 11-6625-2779-14&P NSNReplaceable Parts Iii List of IllustrationsList of Tables Scope Maintenance Forms, Records, and ReportsSection Introduction Reporting Equipment Improvement Recommendations EIR Administrative StorageDestruction of Army Electronics Materiel Items Comprising an Operable Equipment Specifications Voice Frequency Level Measurements 20Hz to 20kHzSection Section General Information IntroductionInstrument Identification Accessory Equipment SuppliedAccessory Equipment Supplied BAL ModificationPower Requirements Section Installation InspectionWarranty Exception BatteryInstallation and Removal of Battery Cover RemovalSection Controls Connectors IndicatorsBattery 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 Crosstalk Measurements Identifying Noise CharacteristicsTransmission Loss Measurements Crosstalk Correction FactorMeasurements in DBC Input jacks are connected in parallel. If a 600 ohm Reinstall the set in its case0dBm 135 BALStep Procedure Level Measurement Noise Metallic MeasurementsExample Noise-to-Ground Measurements Balance MeasurementRecorder Calibration Transmission Loss MeasurementBlock Diagram Description Section Theory of Operation IntroductionDetailed Circuit Description Simplified Dial BAT FunctionInput Amplifier A3. Schematic No Range Attenuator A2Range Attenuator Setting AttenuationFILTERS. Schematic No 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 Factory Selected Values Section Maintenance IntroouctionInstrument Recommended Type Required Characteristics Model BAL ConversionFunction CARRIER, 75 Unbal Performance ChecksLevel Accuracy Checks TMS, TermFrequency Unbal Carrier Accuracy CheckRange 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 MSG dBm 3kHz Flat dBm 15kHz Flat dBm Program dBm Filter Response ChecksFilter Response Checks TMS Brdg Input BalanceBridging Loss Input TMS BrdgUnbal Calibration Adjustment and Calibration ProcedurePower Supply Check Attenuator CalibrationBalance Check Frequency Response AdjustmentCommon Mode Adjustment Filter Calibration Assembly RemovalTroubleshooting Procedures Troubleshooting Tree Front Panel Trouble Analysis Dial BATRange Troubleshooting Front Panel TroubleshootingFunction Troubleshooting Front Panel Trouble Analysis ContdTroubleshooting the Meter Amplifier and Detector Troubleshooting Input AmplifierFilter Troubleshooting Defective FunctionTip to Ring Tip to Ground Ring to Ground Function Switch Resistance ValuesFunction Input Jacks DIAL/AC MON Jacks Brdg TermRange dBm Pin 1 to Pin 2 to 11. Factory Selected Values10. Resistance Checks Carrier 75 Unbal Level Accuracy Check Performance Check Test CardDescription Check Carrier 135 BAL Level Accuracy CheckPerformance Check Test Card Contd Carrier 600 BAL Level Accuracy CheckProgram Return Loss CheckFilter Response Checks MSG 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 Fscm Replacement National Part Stock Number FscmPart Number National Stock Number Cross Reference Index National Stock NumberPage Model 3555B Appendix a Code List of Manufacturers Schematic Diagrams Circuit DiagramsFunctional Block Diagram 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 ReferencesAppendix B Maintenance Allocation Section I. Introduction GeneralMaintenance Function Column EntriesTool and Test Equipment Requiremen ts Sec Remarks SecAudio Level Meter TA-885/U TM 11-7725-2779-14&P REF Code NumberTransmission and Noise Measuring SET Appendix CManual Backdating Changes Delete CR6 across M1 Government Printing Office 1980-603-128/66Major General, United States Army Adjutant General General, United States ArmyChief of Staff Active ArmyPage PIN
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