HP TM 11-6625-2779-14-P User Manual
TECHNICAL MANUAL
OPERATOR’S, ORGANIZATIONAL, DIRECT SUPPORT, AND
GENERAL SUPPORT MAINTENANCE MANUAL
(INCLUDING REPAIR PARTS AND SPECIAL TOOLS LISTS)
FOR
METER, AUDIO LEVEL TA-885/U
(HEWLETT-PACKARD MODEL 3555B)
(NSN 6625-00-255-1083)
TM 11-6625-2779-14&P
HEADQUARTERS, DEPARTMENT OF THE ARMY
11 MARCH 1980
TM 11-6625-2779-14&P
This manual contains copyrighted material reproduced by permission of Hewlett-Packard Company. All rights are
reserved.
TECHNICAL MANUAL HEADQUARTERS
DEPARTMENT OF THE ARMY.
No. 11-6625-2779-14&P WASHINGTON, DC, 11 March 1980
OPERATOR'S, ORGANIZATIONAL, DIRECT SUPPORT AND GENERAL
SUPPORT MAINTENANCE MANUAL (INCLUDING REPAIR PARTS AND
SPECIAL TOOLS LISTS) FOR
METER, AUDIO LEVEL TA-885/U
(HEWLETT-PACKARD MODEL 3555B)
(NSN 6625-00-255-1083)
REPORTING ERRORS AND RECOMMENDING IMPROVEMENTS
You can help improve this manual. If you find any mistakes or if you know of a way to
improve the procedures, please let us know. Mail your letter or DA Form 2028 (Recommended
Changes to Publications and Blank Forms), or DA Form 2028-2 located in back of this manual
direct to Commander, US Army Communications and Electronics Materiel Readiness Command,
ATTN: DRSEL-ME-MQ, Fort Monmouth, NJ 07703.
In either case, a reply will be furnished direct to you.
This manual is an authentication of the manufacturer's commercial literature which, through usage, has been found to
cover the data required to operate and maintain this equipment. The manual was not prepared in accordance with
military specifications; therefore, the format has not been structured to consider categories of maintenance.
SECTION 0. INTRODUCTION
Scope ...............................................................................................................................0-1 0-1
Indexes of Publications .....................................................................................................0-2 0-1
Maintenance forms, records, and reports...........................................................................0-3 0-1
Administrative storage.......................................................................................................0-4 0-2
Destruction of Army electronics materiel............................................................................0-5 0-2
Reporting of equipment improvements recommendations (EIR).........................................0-6 0-2
Items comprising an operable equipment ..........................................................................0-7 0-3
I. GENERAL INFORMATION
Introduction.......................................................................................................................1-1 1-1
Accessory equipment supplied..........................................................................................1-9 1-2
Instrument identification....................................................................................................1-11 1-2
150 BAL modification........................................................................................................1-13 1-2
II. INSTALLATION
Inspection.........................................................................................................................2-1 2-1
Warranty exception...........................................................................................................2-3 2-1
Power requirements..........................................................................................................2-5 2-1
Three-conductor power cable ............................................................................................2-7 2-1
Battery..............................................................................................................................2-10 2-1
Installation and removal of battery.....................................................................................2-12 2-2
Cover removal...................................................................................................................2-15 2-2
Repackaging for shipment.................................................................................................2-17 2-2
III. OPERATING INSTRUCTIONS
Introduction.......................................................................................................................3-1 3-1
Controls, connectors and indicators...................................................................................3-4 3-1
Operation..........................................................................................................................3-6 3-1
Battery..............................................................................................................................3-8 3-1
Level and noise measurements.........................................................................................3-12 3-5
Level measurements.........................................................................................................3-14 3-5
Noise measurements ........................................................................................................3-28 3-7
Recorder compatibility.......................................................................................................3-41 3-8
Applications......................................................................................................................3-45 3-8
Transmission loss measurements.....................................................................................3-48 3-10
Para Page
i
SECTION III. OPERATING INSTRUCTIONS (Cont.). Para Page
Crosstalk measurements...................................................................................................3-53 3-10
Identifying noise characteristics.........................................................................................3-57 3-10
Measurements in DBC ......................................................................................................3-64 3-11
Measurement procedures..................................................................................................3-67 3-12
150 BAL conversion..........................................................................................................3-69 3-12
IV. THEORY OF OPERATION
Introduction.......................................................................................................................4-1 4-1
Block diagram description.................................................................................................4-7 4-1
Detailed circuit description.................................................................................................4-16 4-2
Range attenuator A2.........................................................................................................4-18 4-3
Input amplifier A3..............................................................................................................4-20 4-3
Filters................................................................................................................................4-25 4-4
Meter amplifier..................................................................................................................4-30 4-7
Detector............................................................................................................................4-32 4-7
Power supply and series regulator.....................................................................................4-37 4-8
V. MAINTENANCE
Introduction.......................................................................................................................5-1 5-1
Factory selected values.....................................................................................................5-4 5-1
150 BAL conversion..........................................................................................................5-6 5-1
Performance Checks.........................................................................................................5-7 5-2
Adjustment and calibration procedure................................................................................5-14 5-8
Assembly removal.............................................................................................................5-25 5-10
Troubleshooting procedures..............................................................................................5-27 5-10
Factory selected values.....................................................................................................5-39 5-15
VI. REPLACEABLE PARTS
Introduction.......................................................................................................................6-1 6-1
Ordering information.........................................................................................................6-4 6-1
VII. CIRCUIT DIAGRAMS
Introduction.......................................................................................................................7-1 7-1
Functional block diagrams.................................................................................................7-3 7-1
Schematic diagrams .........................................................................................................7-5 7-1
APPENDIX A. REFERENCES.................................................................................................................. A-1
APPENDIX B. MAINTENANCE ALLOCATION
SECTION I. Introduction....................................................................................................................... B-1
Il. Maintenance allocation chart for Meter, Audio Level TA-885/U........................................... B-3
III. Tool and test equipment requirements for Meter, Audio Level TA-883/U ............................ B-4
IV. Remarks (Not applicable)
APPENDIX C. MANUAL BACKDATING CHANGES.................................................................................. C-1
ii
Model 3555B Table of Contents
LIST OF ILLUSTRATIONS
Number Page Number Page
1-1.Model 3555B Transmission and
Noise Measuring Set..................................1-1 4-7.Simplified Peak Detection................................4-7
2-1.Power Plugs.................................................2-1 5-1.Balanced BNC to 310 Plug..............................5-2
3-1.Front Panel Controls, Indicators, 5-2.Level Accuracy Check.....................................5-2
and Connectors.........................................3-2 5-3.+20dBm and +30dBm Level
3-2.Side Panel Controls and Connectors.............3-4 Accuracy Check............................................5-4
3-3.Impedance Matching 3555B to Recorder......3-8 5-4.Return Loss Test Set-Up..................................5-5
3-4.Recorder Compatibility Chart........................3-9 5-5.Filter Response Test Set-Up............................5-5
3-5.Simplified Send/Receive Test Set-Up...........3-9 5-6.Bridging Loss Test Set-Up...............................5-6
3-6.Typical Test Set-Up for Measuring 5-7.Input Balance Test Set-Up...............................5-7
Insertion Loss..........................................3-10 5-8.Troubleshooting Tree.....................................5-11
3-7.Test Set-Up for Measuring 7-1.Functional Block Diagram..........................7-3/7-4
Crosstalk Coupling Loss..........................3-11 7-2.A1 Function Assembly Schematic and
3-8.Simple Test for Inductive and Component Location...............................7-5/7-6
Capacitive Coupling.................................3-12 7-3.A2 Range Attenuator and A3 Input
4-1.Simplified Block Diagram..............................4-1 Amplifier Schematic and Component
4-2.Simplified DIAL BAT Function......................4-2 Location..................................................7-7/7-8
4-3.Simplified NG Function.................................4-3 7-4.A4 Filter Schematic and Component
4-4. Simplified Average Detection........................4-4 Location................................................7-9/7-10
4-5.3kHz FLAT and PROGRAM 7-5.A3 Meter Amplifier, Detector and Series
Weighting Curves......................................4-5 Regulator Schematic and Component
4-6.C-MSG and 15kHz FLAT Locations............................................7-11/7-12
Weighting Curves......................................4-6
LIST OF TABLES
Number Page Number Page
1-1 Specifications...............................................1-0 5-1 Required Test Equipment................................5-1
1-2 Accessory Equipment Supplied.....................1-2 5-2 75 UNBAL Carrier Accuracy Check..................5-3
2-1 Suitable Batteries Meeting 5-3 Carrier 600 BAL and 135 BAL Level
NEDA 202 Specifications...........................2-1 Accuracy Check............................................5-3
3-1 Front, Side and Rear Panel Controls, 5-4 VF/Nm Level Accuracy Checks 600 BAL
Indicators and Connectors...................3-3/3-5 and 900 BAL -80 dBm Through +30 dBm.....5-4
3-2 Crosstalk Correction Factor........................3-10 5-5 Filter Response Checks...................................5-6
3-3 Level Measurement....................................3-13 5-6 Front Panel Trouble Analysis.................5-12/5-13
3-4 Noise Metallic Measurements.....................3-13 5-7 Function Troubleshooting...............................5-14
3-5 Noise-to-Ground Measurements.................3-14 5-8 FUNCTION Switch Resistance Values...........5-15
3-6 Balance Measurement................................3-14 5-9 Range Attenuation and Amplifier Gain...........5-16
3-7 Recorder Calibration...................................3-14 5-10 Resistance Checks........................................5-16
3-8 Transmission Loss Measurement................3-14 5-11 Factory Selected Values................................5-16
4-1 Range Attenuation and Amplifier Gain..........4-4 6-1 Replaceable Parts...........................................6-2
6-2 Part Number-National Stock Number
Cross Reference Index...............................6-10
iii
SECTION 0
INTRODUCTION
0-1. Scope
This manual contains instructions for the operation, organizational maintenance and general support maintenance of
Audio Level Meter TA-885/U. Throughout this manual, the equipment is referred to by its commercial designation of
Hewlett-Packard Model 3555B Transmission and Noise Measuring Set or simply as the 3555B. Appendix A of the
manual contains a list of references and appendix B contains the maintenance allocation chart (MAC).
NOTE
No direct support maintenance functions are authorized for this equipment.
0-2. Indexes of Publications
a. DA Pam 310-4. Refer to the latest issue of DA Pam 310-4 to determine if there are any new editions,
changes, or additional publications pertaining to this equipment.
b. DA Pam 310-7. Refer to DA Pam 310-7 to determine if there are any modification work orders (MWO's)
pertaining to this equipment.
0-3. Maintenance Forms, Records, and Reports
a. Reports of Maintenance and Unsatisfactory Equipment. Department of the Army forms and procedures
used for equipment maintenance will be those described by TM 38-750, The Army Maintenance Management System.
0-1
b. Report of Packaging and Handling Deficiencies. Fill out and forward DD Form 6 (Packaging Improvement
Report) as prescribed in AR 700-58/NAVSUPINST 4030.29/AFR 71-13/MCO P4030.29A, and DLAR 4145.8.
c. Discrepancy in Shipment Report (DISREP) (SF 361). Fill out and forward Discrepancy in Shipment Report
(DISREP) (SF 361) as prescribed in AR 55-38/NAVSUPINST 4610.33B/AFR 75-18 MCO P4610.19C and DLAR 4500.15.
0-4. Administrative Storage
Before placing the TA-885/U in temporary storage (90 days), determine the serviceability of the equipment by
performing the checks in paragraphs 5-7 through 5-13.
0-5. Destruction of Army Electronics Materiel
Destruction of Army electronics materiel shall be in accordance with the instructions in TM 750-244-2.
0-6. Reporting Equipment Improvement Recommendations (EIR)
If your TA-885/U needs improvement, let us know. Send us an EIR. You, the user, are the only one who can tell
us what you don't like about your equipment. Let us know why you don't like the design. Tell us why a procedure is hard
to perform. Put it on an SF 368 (Quality Deficiency Report). Mail it to Commander, US Army Communications and
Electronics Materiel Readiness Command, ATTN: DRSEL-ME MQ, Fort Monmouth, New Jersey 07703. We'll send you
a reply.
0-2
0-7. Items Comprising an Operable Equipment
Audio Level Meter TA-885/U includes the meter, with cover and a power cord. The power cord is stored inside
the cover of the set.
0-3
Section I Model 3555B
Table 1-1. Specifications
VOICE FREQUENCY LEVEL MEASUREMENTS (20Hz balanced and 75 ohms unbalanced.
to 20kHz) Return loss: TERM ONLY
600 ohms: 26dB min 3kHz to 150kHz
Range: -91dBm to +31dBm 135 ohms: 26dB min to 600kHz
75 ohms: 30dB min to 3MHz
Level accuracy: 20Hz to 20kHz: +0.5dB Bridging loss: less than 0.05dB at 10kHz
40Hz to 15kHz: +-0.2dB Balance:
(Levels greater than -60dBm) greater than 70dB to 10kHz
Note: For levels greater than +1 dBm, level accuracy greater than 60dB to 100kHz
specification applies only for frequencies above greater than 40dB to 600kHz
100Hz.
GENERAL
Input: will terminate or bridge 600 ohms or 900 ohms Temperature range: 0°F to 120°F 0 to 95% relative
balanced. humidity
Bridging loss: less than 0.3 dB at 1kHz. The 3555B will operate at -40°F under reduced
Return loss: 30dB min. (50Hz to 20kHz) TERM specifications. At this temperature, attention
Return loss: 30dB min. (50Hz to 2kHz) TERM should be given to noting condition of battery as
only. indicated on Battery Test (DIAL/BAT).
Balance:
greater than 80dB at 60Hz Meter: linear dB scale indicates rms value of input
greater than 70dB to 6kHz signal. 12dB range.
greater than 50dB to 20kHz Meter response
Holding circuit: 700 ohms dc resistance, 60mA Normal: 200ms to indicate a reading to 0dBm on
max. loop current at 300Hz. With holding circuit meter.
in, above specs apply from 300Hz to 4kHz. Damp: 500ms to indicate a reading to 0dBm on
meter.
NOISE MEASUREMENTS
Maximum input voltage
Range: -1 dBm to +121dBm Tip to ring: 150V peak
Tip or ring to ground: 500V peak
Weighting filters: 3kHz flat, 15kHz flat, C-message, and (This is maximum instantaneous voltage. Input
program. Meets joint requirements of Edison circuit will withstand 48V dc CO battery with
Electric Institute and Bell Telephone System. superimposed 90V rms 20Hz ringing voltage or
±130V carrier supply.)
Input: same as for level measurements.
Maximum longitudinal voltage: 200V rms at 60Hz
Noise to ground:
80 kilohms across line AC Monitor: 0.27V rms for 0dBm on meter.
100 kilohms to ground R
-40dB relative to 600 ohms noise metallic at jacks. Sufficient to drive WE 1011B or 52 type
1kHz. headset.
DC Monitor: 1 volt for 0dBm on meter. R
CARRIER FREQUENCY LEVEL MEASUREMENTS kilohms. Jack accepts 310 plug (tip negative).
(30Hz to 3MHz)
Input jacks: will accept Western Electric (WE) 241,
Range: -61dBm to +11dBm 309, 310, 358 plugs. Binding posts accept banana
Level accuracy: Removable shorting bar between sleeve and
600 ohms balanced ground binding posts.
1kHz to 150kHz: ±0.5dB Dial/AC Monitor jacks: will accept WE 289, 310, 347
135 ohms balanced (or 150 ohms balanced) plugs. Accepts WE 1011B lineman's handset or
1kHz to 600kHz: ±0.5dB 52 type headset.
10kHz to 300kHz: ±0.2dB
75 ohms unbalanced Power requirements:
100Hz to 600kHz: ±0.2dB Internal battery: single NEDA 202 45V "B"
30Hz to 1MHz: ±0.5dB battery included. Expected battery life - 180
1MHz to 3MHz: ±0.5dB ±10% of meter reading hours at 4 hours per day at 70° F.
in dBm. AC: 115V or 230V, 48-440Hz, <1W
Input: will terminate or bridge 600 ohms or 135 ohms accepts 310 plug (tip negative) less than 15mA.
= 8 kilohms. Available at DIAL/AC MON
out
= 2
out
plugs, spade lugs, phone tips or bare wires.
External battery: 24V or 48V office battery; jack
1-0
Model 3555B Section I
SECTION I
GENERAL INFORMATION
1-1. INTRODUCTION.
1-2. The Hewlett-Packard Model 3555 B
Transmission and Noise Measuring Set is a versatile set
designed for uses in testing telecommunications
equipment. The extreme sensitivity of this set, linked
with its wide and flat frequency response, make it
suitable for noise and level measurements at voice,
program and carrier frequencies. Levels from -80dBm
to +30dBm (10dBm to +120dBm) full-scale can be
measured and displayed on a meter calibrated to
indicate both in dBm for level measurements and in
dBm for noise measurements.
1-3. The set combines the features of a voice and
noise frequency measuring set and the features of a
carrier frequency measuring set. For voice and program
frequencies impedances of 900 ohms and 600 ohms are
provided, balanced or unbalanced, bridged or
terminated. For noise measurements a noise-to-ground
(Ng) function is provided which provides 40dB of
attenuation for longitudinal noise. For carrier
frequencies 600 ohm, 135 ohm and 75 ohm impedances
are provided. The 600 and 135 function can be either
balanced or unbalanced, bridged or terminated; The 75
function is unbalanced only. Bridging impedance is over
100 kilohms, allowing measurements with a bridging
loss of less than 0.05dB. The meter indicates in dBm
for any selected input impedance.
1-4. The 3555B includes a 3kHz flat, a C-Message, a
Program and a 15kHz flat filter, each easily selectable
by a front panel control. These filters conform to the
standards set up .by the Bell System and Edison Electric
Institute. Other filters are available upon request.
Figure 1-1. Model 3555B Transmission and Noise Measuring Set
1-1
Section I Model 3555B
1-5. A noise-to-ground (Ng) function is included
which permits the measurement of longitudinal noise.
When making noise-to ground measurements the
impedance between INPUT terminals is greater than 80
kilohms and is 100 kilohms between each terminal and
ground. A HOLD function permits holding the line while
noise measurements are being made. The input
circuitry provides 40dB of longitudinal noise attenuation
when noise-to-ground measurements are being made.
1-6. A DIAL/BAT function permits connecting a
lineman's handset to the line for the purpose of dialing
and at the same time connects the front panel meter to
the power supply so that the battery voltage or
unregulated power supply voltage can be monitored.
1-7. Jacks accepting Western Electric type 241, 309,
310, 347, and 358 plugs are provided for INPUT
connections to the 3555B. Dual binding posts accept
banana plugs, wires, lugs or phone tips and a pair of
special connectors permit the attachment of clip leads
from a lineman's handset.
1-8. The Model 3555B can be operated from either
the internal 45V dry cell battery or from the ac line, 115
or 230Vac, 48Hz to 440Hz. A special device is included
in the cover to automatically turn the set off when the
cover is replaced. The set can also be operated from
the central office battery. A jack is provided on the side
of the set for this purpose.
1-9. ACCESSORY EQUIPMENT SUPPLIED.
1-10. The accessory equipment supplied with the
Model 3555B is listed in Table 1-2.
Table 1-2. Accessory Equipment Supplied
-hp- Part No. Description Quantity
8120-1348 Power Cord 1
1470-0026 Battery, 45 Volt dry cell 1
03555-26510 Test Board 1
5000-7135 Decal, 150 BAL 1
1-11. INSTRUMENT IDENTIFICATION.
1-12. Hewlett-Packard uses a two-section serial
number. The first section (prefix) identifies a series of
instruments. The last section (suffix) identifies a
particular instrument within the series. If a letter is
included with the serial number, it identifies the country
in which the instrument was manufactured. If the serial
prefix of your instrument differs from the one on the title
page of this manual, a change sheet will be supplied to
make this manual compatable with newer instruments or
the backdating information in Appendix C will adapt this
manual to earlier instruments. All correspondence with
Hewlett-Packard should include the complete serial
number.
1-13. 150 BAL MODIFICATION.
1-14. The Model 3555B is shipped from the factory
with a 135 BAL function. If a 150 BAL function is
desired instead of the 135 BAL function, the set can be
converted by simply clipping a shorting wire within the
set, applying a 150 BAL decal (supplied with the set)
over the 135 BAL decal and making only one
adjustment.
1-15. For detailed instructions on modification of the
set refer to Paragraph 5-6. If your set is known to be
within specification tolerances a simplified procedure
can be used to modify the set and is described in
Paragraph 3-69.
1-2
Model 3555B Section II
SECTION II
INSTALLATION
2-1. INSPECTION.
2-2. The set was carefully inspected both
mechanically and electrically before shipment. It should
be physically free of mars or scratches and in perfect
electrical condition on receipt. To confirm this, the set
should be inspected for physical damage in transit, for
supplied accessories and for electrical performance.
Paragraph 5-7 outlines the electrical performance
checks using test equipment listed in Table 5-1. If there
is damage or deficiency, see the warranty in the front of
this manual.
2-3. WARRANTY EXCEPTION.
2-4. The battery supplied with the 3555B is
warranted for a period of 60 days, beginning at the time
of receipt of the set. This warranty is based on an
expected battery life of 180 hours at 4 hours per day at
700 F as specified in Table 1-1 in this Manual.
2-5. POWER REQUIREMENTS.
2-6. This set is designed to operate from an internal
45 volt dry cell battery, an external 24 to 48 volt CO
battery or from an ac power source (115/230V, 48 to
440Hz). The power source is selected by the AC/BAT
switch on the side of the, set. The line voltage is
selected by the 115/230 volt slide switch on the rear of
the set. The set is protected by a 0.1 5A slow-blow fuse.
Table 2-1. Suitable Batteries Meeting
NEDA 202 Specifications
Manufacturer Mfr. Part No.
Hewlett-Packard 1420-0026
Western Electric KS-14370
Military BA-59
Eveready 482
Burgess M-30
RCA VS013
Bright Star 3033-158, 30-33
Mallory M-202
Ray-O-Vac 202, P7830
Sears 6461
Wards 42
Wizard 3B6241
Zenith 2783
General W30B
Marathon 4202
National Carbon 482
2-10. BATTERY.
2-11. This set is operated from a single NEDA 202
45V dry cell internal battery or an external 48V CO
battery when the power selection switch, on the side of
the case, is in the DIAL/BAT position. Inserting a
Western Electric plug into the battery jack disconnects
the internal battery. (See Table 2-1 for batteries
suitable for use in this instrument.
2-7. THREE-CONDUCTOR POWER CABLE.
2-8. To protect operating personnel, the National
Electrical Manufacturers' Association (NEMA)
recommends that the panel and cabinet be grounded.
This set is equipped with a three-conductor power cable
which, when plugged into an appropriate receptacle,
grounds the set. The offset pin on the power cable
three-prong connector is the ground wire. This power
cable is detachable from the set and is stored inside the
front cover.
2-9. Figure 2-1 illustrates the standard power plug
configurations that are used throughout the United
States and in other countries. The -hp- part number
shown directly below each plug drawing is the part
number for a 3555B power cord equipped with the
proper plug. If the appropriate power cord is not
included with the instrument, notify the nearest HewlettPackard office and a replacement cord will be provided.
Figure 2-1. Power Plugs.
2-1
Section II Model 355B
2-12. INSTALLATION AND REMOVAL OF
BATTERY.
2-13. To install or replace a battery, turn the four 1/4
turn fasteners on the battery cover on the rear of the
case counterclockwise to remove the cover. Lift off the
cover, lift the battery out of its recess and unplug the
three-prong connector.
2-14. Reverse the above procedure when installing a
new battery.
2-15. COVER REMOVAL.
2-16. To remove the cover from the instrument,
release the two spring latches on either side of the
instrument, then lift cover. When replacing the cover,
first check the latches for released position; then place
cover in position for latching. The power cord is stored
inside the cover by wrapping it around the retainer
fastened inside the cover.
CAUTION
DO NOT FORCE COVER INTO
PLACE. THERE IS A PROJECTION
ON THE COVER WHICH TURNS THE
POWER SWITCH TO THE OFF
POSITION TO PRESERVE BATTERY
LIFE. IF THIS IS NOT BINDING, THE
COVER FITS EASILY INTO PLACE.
2-17. REPACKAGING FOR SHIPMENT.
2-18. The following is a general guide for repackaging
at instrument for shipment. If you have any questions,
contact your local Sales and Service Office. (See
Appendix for locations.)
a. Place instrument in original container if
available. If not available, one can be
purchased from your nearest -hp- Sales
and Service Office.
b. Wrap instrument in heavy paper or plastic
before placing in inner container.
c. Use plenty of packing material around all
sides of instrument.
d. Use a heavy carton or wooden box to
house the instrument and inner container
and use strong tape or metal bands to seal
the shipping container.
e. Mark shipping container with "Delicate
Instrument" or "Fragile".
2-2
Section III Model 3555B
SECTION III
OPERATING INSTRUCTIONS
3-1. INTRODUCTION.
3-2. The Model 3555B Transmission and Noise
Measuring Set is an extremely versatile transmission and
noise measuring set which satisfies many of the
requirements in testing telecommunications equipment.
The 3555B features a choice of 900 or 600 ohms bridging
or terminated for voice frequencies and 600, 135 or 75
ohms bridging or terminate for carrier frequencies. Noiseto-ground and noise Metallic may be measured with 3kHz
Flat, C-Message or 1 5kHz Flat weighting. A HOLD
function permits seizing the line while measurements are
being made at voice and program frequencies. The set is
portable and operates from the internal battery, office
battery or ac power source.
3-3. This section of the manual contains all the
information necessary in the operation of the 3555B along
with a description of all controls, connectors and
indicators.
3-4. CONTROLS, CONNECTORS AND
INDICATORS.
3-5. Figure 3-1, 3-2 and Table 3-1 illustrate and
describe the function of all front and side panel controls,
indicators and connectors.
3-6. OPERATION.
3-7. To operate the Model 3555B, refer to figure 3-1
and perform the following steps:
a. Before connecting the 3555B to an ac power
source, insure that the 115/230 volt switch is
positioned to indicate the line voltage to be
used. Some earlier instruments did not have
the 115/230 volt selector switch. To change
these instruments, jumper wires must be
changed on the power transformer. Refer to
Appendix C for a wiring diagram of the two
configurations.
b. If the set is to be operated from the internal
battery or from an external office battery,
place the AC/BAT switch (located on the side
of the set) to the BAT position, using a small
pointed object; if the set is to be operated
from the ac line, place the AC/BAT switch to
the AC position. For operation from a 24 or
48V office battery, connect a patch cord with
a Western Electric 310 plug to the battery
jack on the side of the case and then connect
the cord to the office battery on the test
board or bay. Inserting the plug disconnects
the internal battery. The office battery is
arranged for -48V or -24V ±2V with the
negative terminal of the battery connected to
the tip and the ground terminal connected to
the sleeve. Current consumption by the
3555B is approximately 15mA.
WARNING
DURING BATTERY OPERATION, THE
"G" BINDING POST MUST BE
CONNECTED TO EARTH GROUND.
CAUTION
THE CORD MUST BE CONNECTED TO
THE MEASURING SET BATTERY
JACK FIRST AND THEN PLUGGED
INTO THE BATTERY SUPPLY TO
AVOID SHORTING THE OFFICE
BATTERY TO GROUND.
c. Turn the POWER switch to ON and depress
the DIAL/BAT pushbutton on the FUNCTION
switch. The meter pointer should indicate in
the BAT GOOD area indicating that the
battery condition is good if the set is being
operated from the internal battery. The
meter will also monitor the ac supply voltage
or the external office battery voltage,
providing an indication of low voltage should
it exist. The voltage should cause meter
deflection above the lower end of the green
BAT GOOD area for proper set operation.
3-8. BATTERY.
3-9. The internal dry cell battery has a voltage range
between 45 volts when new to 24 volts at cut-off which is
the end of useful life. The cut-off voltage corresponds to
the left end of the green BAT GOOD area on the meter.
The condition of the battery and the approximate time to
cut-off can be estimated by observing the position of the
meter pointer in the BAT GOOD area.
3-10. The internal battery is of the carbon-zinc type with
its attendant limitations due to temperature. The service
obtained from carbon-zinc batteries depends on factors
such as current drain, discharge temperature, discharge
time and storage prior to use. The battery supplied with
the 3555B should provide in excess of 180 hours of
operation based on a 4 hours/day duty cycle at 77° F (25°
C). At other temperatures this time will change. At
temperatures above 131° F (55° C) the batteries may fail
suddenly while at temperatures below 40° F (-20° C), the
service life will be short.
3-1
Section III Model 3555B
Figure 3-1. Front Panel Controls, Indicators, and Connectors
3-2
Model 3555B Section III
Table 3-1. Front, Side and Rear Pane
(1) S and G Jacks: Binding posts accepting banana
plugs, spade lugs, phone tips or bare wires for
connection to the case ground (G) and sleeves (S)
of all INPUT jacks (12) and DIAL/AC MON jacks
(10) and (11).
(2) Shorting Strap: A swing-away shorting strap
connecting the S and G terminals together which
may be used to isolate the jack sleeves from case
ground. Not for use with type 347 plugs.
(3) WTG Switch: Selects weighting filters for noise
measurements. These filters are selectable only
when the INPUT switch is in one of the two NOISE
positions. The 3kHz FLAT, C-MSG, 15kHz FLAT
and PROG filters all conform to the standards set
up by the Bell System and Edison Institute for
measuring message circuit noise.
(4) RANGE SWITCH: Selects dBm or dBm ranges of
input sensitivity. The RANGE switch markings
correspond to the 0 markings on the meter scale
(6). The black markings are dBm for transmission
measurements and the blue markings are dBrn for
noise measurements.
(5) RESPONSE Switch: Selects NORM meter
response for transmission level measurements or
DAMP for noise measurements where noise is
impulsive in nature.
(6) Meter: A taut band individually calibrated meter
with shaped pole pieces to provide a linear dBm
indication with equal accuracy and resolution over
the entire meter scale. The dBm scale is marked
in black and has 0.1dB resolution for transmission
measurements. The 0 marking at the right end of
the scale corresponds to the black RANGE switch
setting. The dBm scale is marked in blue for noise
measurements. The 0 marking at the left end of
the scale corresponds to the blue RANGE switch
setting. The green arc marked BAT GOOD
corresponds to the green DIAL BAT pushbutton for
checking the power source. The left edge of the
arc corresponds to the battery cut-off voltage of 24
volts and the right edge (meter full-scale)
represents 60 volts which is the maximum voltage
that can be used to power the set without internal
damage.
(7) POWER ON/OFF Switch: turns on all power to the
set. The set operates from either 115 volts or 230
volts ac, the internal 45 volt dry cell battery or from
an external office battery supply.
(8) INPUT Switch: Selects TMS, either BRDG or
TERM for transmission measurements and NOISE,
either BRDG or TERM for noise measurements.
For noise measurements the switch must be in
Controls, Indicators and Connectors either the
NOISE BRDG or the NOISE TERM before the
NOISE WTG filters can be selected.
(9) FUNCTION Switch: A series of interlocking
pushbutton switches (with the exception of the
HOLD switch which is push-push type) with the
following functions:
a. VF/Nm
1. HOLD: Applies a dc holding bridge
across the metallic line for the NG, 900
and 600 functions. The HOLD
pushbutton is the push-push type, ie,
push to make and push to break. The
HOLD function cannot be
accomplished when any one of the
CARRIER pushbuttons is depressed.
2. DIAL/BAT: Connects the multiple
INPUT jacks in parallel with the
DIAL/AC MON jacks for the dial and
talk operation. The circuit is arranged
for loop dialing and the line under test
must supply talk battery. Connects the
meter circuit and a load to the internal
power supply to check the condition of
the battery, ac power or external office
battery as indicated on the green meter
scale. POWER (7) must be ON for the
battery test.
3. NG: Selects the noise-to-ground input
circuits for measuring longitudinal
noise. Attenuation of 40dB is inserted
by this circuit. Earth ground should be
connected to the black G binding post
(1)
4. 900: Selects the input circuitry for
balanced 900 ohm circuits. This
function selects a low frequency
transformer for voice frequencies.
Response of this transformer is 20Hz
to 20kHz.
5. 600: Selects the input circuitry for
balanced 600 ohm circuits. A low
frequency transformer is selected for
this function.
b. Carrier
1. 600: Selects the input circuitry for
balanced 600 ohm circuits. A high
frequency transformer is selected for
this function. Response of this
transformer is 1kHz to 600kHz. The
HOLD function is not operative in any
of the carrier functions.
3-3
Section III Model 3555B
Figure 3-2. Side Panel Controls and Connectors
3-4
Model 3555B Section III
Table 3-1. Front, Side and Rear Panel Controls, Indicators and Connectors (Cont’d)
2. 135: Selects the input circuitry for 135
ohm balanced circuits. A high
frequency transformer is selected for
this function.
3. 75: Selects the input circuitry for 75
ohm unbalanced operation. Only the
75 ohm jack can be used for this
function. This function does not utilize
an input transformer, therefore the
maximum bandwidth is available on
this function. This jack accepts a 358
plug.
(10) DIAL/AC MON: A set of multiple jacks accepting
Western Electric type 310 or 347 plugs, 289 dual
plugs and a pair of special clip posts marked T and
R which accept a Western Electric 1011IB
lineman's handset for the dial and talk operation
when the FUNCTION pushbutton marked
DIAL/BAT is depressed. Loop dialing is used and
the circuit must supply talk battery. When any
other FUNCTION pushbutton is depressed, the tip
and ring of these jacks are connected to the AC
MON output of the internal amplifiers for
monitoring purposes.
(11) DC MON: Accepts a Western Electric 310 or 347
plug for tip negative and sleeve connections to an
external dc recorder. Output voltage is
proportional to the input voltage on any one setting
of the RANGE switch.
(12) INPUT: A set of multiple jacks accepting Western
Electric 241 (or 289), 309, 310 and 358 plugs and a
pair of binding posts marked T and R for banana
plugs, spade lugs, phone tips or bare wires
providing connection to the input circuitry of the
measuring set. When the DIAL BAT pushbutton is
depressed, the INPUT jacks are connected in
parallel with the DIAL/AC MON jacks.
(13) Battery Cover: Removeable by four 1/4 turn screw
fasteners to expose the internal battery for
replacement.
(14) 48V 310: A jack accepting a Western Electric 310
plug with tip negative and sleeve ground to supply
external office battery power to the set. Insertion
of a 310 plug into this jack disconnects the internal
battery. The BAT-AC switch (16) must be set to
BAT for office battery operation.
CAUTION
WHEN OPERATING FROM AN EXTERNAL
BATTERY, CORD SHOULD BE CONNECTED
TO MEASURING SET FIRST, THEN PLUG
INTO BATTERY SUPPLY TO AVOID
SHORTING THE OFFICE BATTERY.
(15) 0.15A-SPARE Fuse: A 0.15A slo-blo fuse and a
spare for measuring set protection when operating
from AC power. Fuses are not used when the set
is battery powered.
(16) BAT-AC Switch: A slide switch for selecting the ac
power source or the internal battery and office
battery jack, (14), power source. The switch may
be operated by a small screwdriver or pointed tool
inserted into the slot in the switch.
(17) AC Power Receptacle: A 3 prong power receptacle
for the special power cord stored inside the front
cover. The BAT-AC switch (16), must be
positioned to AC for this power source.
3-11. High storage temperature is damaging to dry
cells and tends to reduce shelf life. Low storage
temperature is beneficial to battery life although the
battery should be warmed to room temperature prior to
use. Turning off the set when not in use and
consideration of the above factors will maximize battery
life. The instant turn characteristics of this set with no
warm-up time required allows turning off between
measurements.
NOTE
If the battery voltage indication drops below
the left end of the arc on the meter face the
set will not operate properly. This will be
noted by a slow oscillation of the meter. If
this symptom is encountered, depress the
DIAL/BAT pushbutton and check the battery
condition. If the indication is to the left of
the arc on the meter face, replace the
battery.
3-12. LEVEL AND NOISE MEASUREMENTS.
3-13. Since the 3555B is both a level measuring set
and a noise measuring set, the procedure for making
these measurements will be treated separately. Level
measurements can be made at voice frequencies and
carrier frequencies. Since the procedure for making
voice and Carrier level measurements are identical
except for the FUNCTION pushbutton utilized, only one
procedure will be described in detail.
3-14. LEVEL MEASUREMENTS.
3-15. The 3555B can be used as a wide range and
wide
3-5
Section III Model 3555B
frequency Transmission Measuring Set (TMS) for voice,
program and carrier multiplex measurements. The set will
operate over a wide range of environmental conditions and
maintain a high degree of accuracy.
3-16. In general, transmission level measurements are
made by connecting the circuit under test to the INPUT
jacks with a suitable patch cord, selecting the proper
bridging or terminate condition and impedance, and then
operating the RANGE switch to provide an on-scale meter
indication. Transmission level measurements are made
with the INPUT switch in TMS position either bridging or
terminated. In this position, the set has its maximum
frequency range.
3-17. The multiple INPUT jacks and binding posts
accept the Western Electric 309, 310 and 358 single plugs
and the 241 or 289 twin plug. The two red binding posts
marked T (tip) and R (ring) will accept banana plugs,
spade lugs, phone tips or bare wires. These jacks and
binding posts are all connected in parallel and only one
should be used at a time. A patching cord such as the
Western Electric 3P12H, consisting of a cord with a 310
plug on one end and a 309 plug on the other end, should
be kept with the instrument as a universal patch cord. The
75 ohm jack accepts Western Electric type 358 plugs for
75 ohms. unbalanced carrier measurements.
3-18. The sleeves of all the INPUT and DIAL jacks are
connected together and to the black binding post marked
S. The binding post in turn, is connected through a swingaway shorting strap to a second black binding post marked
G. This binding post is the measuring set case ground.
When it is necessary to establish a battery or ground
connection on the sleeve for PBX test purposes, this
shorting strap may be disconnected by loosening the black
binding posts and swinging away the strap. A cord is then
connected to the S terminal and may be connected to the
battery or ground for the test. Type 347 plugs must not be
used when the shorting strap is removed.
3-19. The multiple jacks marked DIAL/AC MON are
connected in parallel and accept a 310 or a 347 single plug
or a 289 dual plug. A dial with the impulse springs
connected to the tip and ring of a 310 or 347 plug may be
used or a lineman's handset such as the Western Electric
1011 B may be connected to the two square clip posts for
the dialing and talk operation. When the FUNCTION
pushbutton marked DIAL/BAT is depressed, the DIAL
jacks are connected to the INPUT jacks and a number may
be dialed on the line connected to the INPUT jacks. The
circuit is arranged for loop dial operation and the circuit
under test must supply talk battery.
3-20. Once the switching equipment has been seized by
the dialing operation, the connection can be held by
depressing the HOLD pushbutton. This places a dc bridge
consisting of a high impedance retardation coil, across the
INPUT terminals. This coil has negligible effect on
measurements of voice frequencies. Once any other
pushbutton is depressed, the AC output of the internal
amplifier circuit is returned to the DIAL/AC MON jacks for
an external head Model 3555B phone which can be used
to monitor the noise or tones being measured. The
lineman's hand set which was used for the dialing
operation can be used for monitering by leaving it
connected to the clip posts. The jacks marked 310 will
accept a head phone or recorder connected to the tip and
ring of a 310 plug or tip and sleeve of a 347 plug. The
performance of the set is not affected by this output and
any impedance head-phone may be used.
3-21. The DIAL/BAT function also checks the power
source used. The green arc on the meter marked BAT
GOOD corresponding to the green BAT marking on the
pushbutton, indicates the range of voltages for proper
operation. Full scale corresponds to 60 volts and the left
end of the arc corresponds to the battery cut-off voltage of
24 volts. Thus the remaining battery life can be estimated
by noting the position of the pointer in the green arc.
Since the set POWER must be turned ON to perform this
check, the battery is properly loaded to give a true
indication of its condition. When operating from the
external office battery or AC power, the meter monitors
this voltage to indicate if it is the correct level to properly
power the set. The POWER switch turns OFF and ON all
power to the set.
3-22. The remaining FUNCTIONS are used to set up the
input conditions. The Ng function will be discussed under
the paragraph heading, "NOISE MEASUREMENTS". The
impedance of the set is selected by the pushbuttons
marked 900 and 600 for voice frequencies and 600, 135
and 75 for carrier frequencies. The 900 and 600 ohm
impedances are normally used for loop plant testing while
600, 135 and 75 ohms are usually reserved for carrier
system measurements. A bridged or terminated condition
is determined by the position of the INPUT switch. Using
this procedure, the meter will always indicate in dBm for
the impedance selected, bridging or terminated. The
terminations, when used, are provided with a dc blocking
capacitor. Accidental application of carrier or telegraph
battery, office battery or ringing voltage will not damage
the set. The pushbutton marked HOLD bypasses the
INPUT switch and terminates the circuit in addition to
placing the holding bridge across the line that is connected
to the INPUT. When the INPUT switch is in either of the
NOISE positions, weighting filters can be selected by the
NOISE WTG switch for noise measurements.
3-23. The RANGE switch selects the dBm range of the
meter. To avoid overloading the set, turn the RANGE
switch to +30dBm when connecting a circuit for testing.
Once the circuit connection is established turn the RANGE
switch counterclockwise until an on-scale indication is
obtained. The black dBm marking on the RANGE switch
identifies the input level required to deflect the meter to
the 0 mark on the black scale. The meter uses shaped
pole pieces to present linear dBm markings on the scale
with marks at 0.1 dBm increments. The accuracy and
resolution of this type of meter is the same at any point on
the scale and it is not necessary to keep the pointer in the
upper portion of the scale for maximum accuracy. The
accuracy of the set is not affected by the position of the
set. This type of meter will have the pointer off-scale to
the left
3-6
Model 3555B Section III
when no input signal is present and a mechanical zero
adjust is not required. The actual input level to the set is
the algebraic sum of the black dBm meter scale and black
RANGE setting. For example, RANGE is set to 40dBm
and the meter indicates -6.3dBm. The input level is then (-
40) + (-6.3) = -46.3dBm. If the RANGE switch is at
+20dBm and the meter indication is 4.7dBm, the level is
(+20) + (4.7) = +15.3dBm.
3-24. All panel markings corresponding to the proper
dBm markings on the RANGE switch and meter face are in
black, as is the TMS position of the INPUT switch. The
blue markings correspond to the settings for noise
measurements as discussed in paragraph 3-28. The
response of the meter rectifier circuit is RMS which allows
the set to measure the true power of any arbitrary input
waveform provided the crest factor does not exceed 4:1.
Crest factor is defined as the ratio of the peak value of the
waveform to the RMS value of that waveform. In most
telephonic measurements, consideration of this crest
factor is not necessary.
3-25. The balanced input to the set is achieved through
the use of two repeat coils, one for voice frequencies from
20Hz to 20kHz and the other for carrier frequencies from
10kHz to 600kHz. The maximum high frequency range is
achieved through the use of the 75 ohm functions and the
75 ohm jack. This input bypasses both input repeat coils,
thus allowing measurements from 30Hz to 3MHz. This
high frequency range is limited to 600kHz on the +20 and
+30dBm ranges. The maximum longitudinal input voltage
is 150 volts peak between tip and ring and 200 volts rms at
60Hz between either tip or ring and ground.
3-26. The switch marked RESPONSE determines the
speed of the meter response and is usually left in the
NORM position for transmission measurements.
3-27. The jack marked DC MON accepts a Western
Electric 310 or 347 plug with connections to the tip and
sleeve. The dc voltage supplied by this jack can be used
to operate a dc potentiometric recorder requiring 1V or a
dc galvanometric recorder requiring 500uA. The dc output
is proportional to input level on any one range and not
meter deflection since the meter is logarithmically scaled.
Knowing the current required to drive the recorder full
scale and the input impedance of the recorder, enter these
numbers into the recorder compatability chart Figure 3-4 to
determine if the recorder is suitable for use with this set. If
these numbers do not fall within the compatability area,
refer to Paragraph 3-41. Connect an input voltage to the
set and adjust the RANGE switch until a near full scale
indication is observed on the meter. 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, which should be near full scale, on the recorder
paper. Decrease the input level until the meter indicates 1dBm. Mark this point on the recorder paper. Continue
until the recorder has been calibrated for each major dBm
division on the meter. The actual input level to the set as
indicated on the recorder will be the algebraic sum of the
RANGE.
3-28. NOISE MEASUREMENT.
3-29. One of the primary functions of this set is to
measure message circuit noise, both metallic and noise-toground. The weighting filters built into this set are switch
selected and their characteristics conform to the standards
set up by the Bell System and Edison Electric Institute.
3-30. In general, noise-metallic measurements are made
by connecting the circuit under test to the INPUT jacks
with a suitable patch cord, selecting the proper bridging or
terminate condition and impedance, selecting the proper
weighting filter and operating the RANGE switch to provide
an on-scale meter indication. Noise measurements
involve many of the same operations as the level
measurements discussed in Paragraph 3-14 and only the
differences will be discussed.
3-31. Four filters are supplied for noise measurements;
C-MESSAGE and 3kHz FLAT for message circuit noise
measurement, a PROG and 15kHz FLAT for broadcast
studio-transmitter links and telephone company program
circuits. These filters are necessary to allow the
measuring set to approximate the response of the human
ear and give an indication representative of a person's
subjectiveness to noise. The frequency response of these
filters is shown in Figures 4-5 and 4-6.
3-32. Once a circuit has been connected, the RANGE
switch is adjusted until the noise fluctuations appear onscale on the meter with normal response, and a two-tothree minute observation of the pointer fluctuations is
made to establish the point at which the pointer appears
most of the time, disregarding the occasional high peaks.
For rapidly fluctuating noise such as atmospheric static or
switching noise, operate the RESPONSE switch to DAMP.
In this position of the switch, the level of the most
frequently occurring peaks should be read. Noise is
specified in dBm (decibels above reference noise) and the
type of filter used is noted, for example, dBmC meaning
C-message weighting is used.
3-33. The noise-metallic level is the algebraic sum of
the indication on the blue dBm meter scale and the blue
dBm RANGE switch setting. For example, RANGE is set
to 20dBm and the meter indicates +7dBm. The noisemetallic level is (20) + (+7) = +27dBm. The RANGE
switch marking indicates the level at the 0dBm mark on
the left end of the meter scale.
3-34. Occasionally other message circuit weightings
such as the older Bell System F1A weighting or the
International Telecommunication Union's CCITT or
psophometric weighting may be required. To convert from
C-message to F1A, subtract 6dBm from the C-message
indication. The units for F1A weighting are dBa, meaning
decibels adjusted. To convert from C-message to CCITT
or psophometric weighting, subtract 1dBm from the Cmessage level as read on the black dBm meter scale and
RANGE switch setting. This will give the noise level in
dBm which is acceptable for psophometric measurements.
3-7
Section III Model 3555B
3-35. As an aid in identifying the source of noise, the
DIAL/AC MON jacks can be used with a monitoring
receiver to listen to the noise which will have
approximately the same quality as that heard by a
subscriber. Particular types of noise like power line
induction, switching noise, atmospheric static, crosstalk or
random noise may be identified by this listening test. To
aid in bringing up the level of the lower frequency power
line noise, the 3kHz flat weighting is used. A substantial
increase in meter indication with the 3kHz flat weighting
indicates the presence of low frequency noise and it will
also sound louder in the monitoring headphone.
3-36. In some cases recording of the noise during a
busy period is necessary. The recorder connections and
operation is discussed in Paragraph 3-27. The calibration
should be done using the dBm scale rather than the dBm
scale and it should be noted that the RESPONSE switch
also damps the recorder.
3-37. Noise-to-ground measurements are made by a
special input circuit arrangement which is used when
either the Ng or Ng HOLD pushbutton is depressed. Dial
and talk may be accomplished on the metallic circuit and
the metallic connection held by using the Ng HOLD
pushbutton. It is necessary to establish a good earth or
system ground and connect it to the black binding post
marked G. The noise-to-ground measurement is 40dB
less sensitive than the noise metallic measurement
because of the voltage divider in the input circuit. This
requires adding 40dB to the meter indication to arrive at
the correct noise-to-ground level. The level is the
algebraic sum of the blue RANGE switch setting and the
blue meter scale indication plus 40dB. For example,
RANGE is set to 20dBm and the meter indicates +3dBm.
3-40. Crosstalk measurements involve low level
measurements and part of the meter indication may be 38 Model 3555B caused by noise in addition to crosstalk.
The general technique is to measure with crosstalk and
noise present and then measure noise alone. A
correction factor must then be applied and can be found
in Table 3-2.
3-41. RECORDER COMPATIBILITY.
3-42. If an external recorder is to be used to monitor the
dc output of the 3555B, the Recorder Compatibility graph,
Figure 3-4 should be consulted to determine if your
particular recorder can be used. Recorders with input
characteristics that fall below the compatibility area can
be used provided a suitable resistor is used between the
3555B dc output and the recorder input.
3-43. To choose the value of this resistance, simply
follow the line designating the full scale current of your
recorder, horizontally until it intersects the top line in the
Recorder Compatibility graph. From this intersection
follow the vertical line to find the total impedance RT
required for full scale deflection (see Figure 3-3). The
input impedance of the recorder should be subtracted
from this value RT to determine the value of R1. For
example, assume that your particular recorder has an
input impedance of 2000 ohms with a full scale sensitivity
of 20uA. Follow the 20uA line to the right until it
intersects the top line at 48 kilohms. The value of R1 will
then be 48 kilohms -2 kilohms input impedance = 46
kilohms.
3-44. Recorders with input characteristics that fall
above the compatibility area in Figure 3-4 cannot be used
to monitor the 3555B dc output since full scale deflection
of the recorder cannot be accomplished by the 3555B.
The noise-to-ground level is 20 + (+3) +40= 63dBm.
Some telephone company operating procedures disregard
the 40dB correction factor in which case the noise-toground level would be 20 + 3 = 23dBm.
3-38. The Nm and Ng indications can be used to
compute the balance of a facility since balance is defined
as the degree of rejection of longitudinal signals. The
degree of balance in dB where the major part of noisemetallic is due to noise-to-ground, is given by the
Figure 3-3. Impedance Matching 3555B to Recorder
equation, Balance in dB = Nm - Ng. For example, if the
noise-metallic level of a circuit is +26dBm and the noiseto-ground of the same circuit is +9OdBmC, the balance in
dB is (+26) - (+90) = 64dB. In the case mentioned above
where the 40dB correction factor is neglected, the balance
in dB = (Nm) (Ng + 40).
3-39. Other general purpose uses of the 3555B are
volume and crosstalk measurements. The ballistic
characteristics of the set make it approximately correct for
VU measurements. The RANGE switch should be
adjusted until the meter pointer fluctuations are on-scale
and should be observed for the maximum of the
frequently occurring peaks, disregarding the occasional
high peaks. The meter indication in dBm is equal to VU
(volume units.)
3-45. APPLICATIONS.
3-46. Sometimes it is necessary to transmit or send a
tone on a line and then measure the received signal
coming back on the same line. Rather than change
connections back and forth between the 3555B and 236A
Oscillator when changing from SEND to RECEIVE and
thus take a chance on dropping the line, it is much more
convenient to make one set of connections and then
select SEND or RECEIVE by means or a switch. Refer to
Figure 3-5.
3-47. By utilizing the test set-up shown in Figure 3-5,
send and receive can be accomplished with a minimum
number of operations. To dial, set both function switches
to DIAL and dial the desired line on the butt-in. To send,
change the
3-8
Model 3555B Section III
Figure 3-4. Recorder Compatibility Chart
Figure 3-5. Simplified Send/Receive Test Set-up
3-9
Section III Model 3555B
236A FUNCTION switch to 600 HOLD or 900 HOLD,
depending on the impedance required. To receive a
tone, set the 3555B FUNCTION switch to either 600
HOLD or 900 HOLD (whichever is appropriate) and
change the 236A FUNCTION switch to DIAL. To send
again, simply change the 236A to 600 HOLD or 900
HOLD. If holding is not required or dialing is not
required, simply select the impedance and switch back
and forth on the 236A FUNCTION switch.
3-48. TRANSMISSION LOSS MEASUREMENTS.
3-49. Transmission loss is defined as the ratio of
power from a transmission line by a receiving terminal
to the power available from the sending equipment and
is dependent on three factors; power dissipated by the
dc resistance of the line, power losses because of
impedance mismatch, power transferred to other circuits
by inductive or capacitive coupling. (See Figure 3-6).
3-50. These factors are difficult to measure
separately. Their sum, however, is relatively easy to
measure with the -hp- 236A/3555B combination.
3-51. Figure 3-6 shows a typical transmission loss
measurement setup. The oscillator is adjusted for a
reference level and the signal is measured at the other
end of the line with a level meter. Loss measurements
are usually made at various frequencies to determine
the response of the line.
3-52. Ideally the man at each end of the line will have
both an oscillator and a Transmission Measuring Set
(TMS) so that the loss can be measured in both
directions, If the line that is being tested passes through
central office switching equipment, the oscillator or TMS
at the remote end is placed in the DIAL mode and the
lineman's handset connected to the DIAL posts,
permitting the repairman to bypass the instrument
circuitry and dial his test board at the central office.
Tests are then made in the 600 or 900 ohm HOLD
positions, which provide a dc path to hold the switching
relays.
3-53. CROSSTALK MEASUREMENTS.
3-54. Crosstalk is interference on a transmission line
caused by inductive and capacitive coupling between
pairs of transmission lines in close proximity. Crosstalk
can be classified as near-end and far-end. Far-end
crosstalk is interference at the end of the transmission
line opposite the , signal source while near-end crosstalk
is interference detected at the same end of the line as
the signal source.
Table 3-2. Crosstalk Correction Factor
dB Correction Factor
(Crosstalk + Noise) in dB Crosstalk in dB =
Minus Noise Alone in dB (Crosstalk + Noise)
Minus Correction Factor
1 7
2 4
3 3
4 to5 2
6 to 8 1
9 and above 0
3-55. Since different frequency bands are used for
each direction of transmission on two wire carrier
systems, near-end crosstalk cannot be detected. The
situation is quite different, however, for far-end crosstalk
since it is in the same frequency band as the desired
signal and can be detected.
3-56. Referring to Figure 3-7, one line is designated
A-B and the other designated C-D with A and C
representing the near-end of one of the pairs, and band
D representing the far-end of the other pair. First
measure the transmission loss between A and B. Then
measure the transmission loss from A to D. The
crosstalk coupling loss in dBx is the difference in the
reading from A to B and the reading from Ato D.
3-57. IDENTIFYING NOISE CHARACTERISTICS.
Figure 3-6. Typical Test Setup for Measuring Insertion Loss
3-10
Model 3555B Section III
Figure 3-7. Test Setup for Measuring Crosstalk Coupling Loss
3-58. Normally, a frequency selective voltmeter is
used to identify the characteristics of transmission line
interference in order to trace it down to its origin and
apply the appropriate corrective action. As an expedient
for troubleshooting, there are several subjective
measurements that the 236A/3555B can make to help
identify the interference characteristics.
3-59. Since power line noise is the most common
nuisance, a quick check with the 3555B should be made
first. By noting the difference in noise readings between
the 3kHz FLAT and C-message weighted modes, an
indication of line frequency disturbance can be
ascertained if the 3kHz flat mode shows a substantially
higher reading.
3-60. As a further aid in identifying noise, the
lineman's handset can be connected to the AC
MONITOR terminals and an aural analysis made.
Although the handset will not respond to 60Hz, line
interference is usually very rich in odd harmonics and
180Hz can easily be identified. This test also helps to
identify "babble" and other audio frequency interference.
3-61. Vagrant noise, such as atmospheric noise, can
be analyzed by connecting a strip chart recorder to the
DC MONITOR terminals. Long-term seasonal and
temperature effects can also be measured very
conveniently with a recorder.
3-62. Frequency of strong interfering periodic signals,
such as radio transmitters, can be roughly determined
with the 236A and 3555B. The 236A is connected to
one end of the line and the 3555B to the remote end, as
with transmission loss measurements. The oscillator
output is increased until the test meter barely indicates a
signal above the noise. The oscillator frequency is then
changed very slowly while the repairman observes the
3555B for a beat. By tuning for a beat, the frequency of
oscillator frequency dial to an accuracy of approximately
±3%. In practice, this measurement would probably be
made using a "loop around" technique. The oscillator
would be connected to a quiet line at the remote location
and this line would be tied to the noisy line back at the
central office. This permits one man to operate both the
oscillator and the test meter.
3-63. When a current flows through a conductor, it
sets up two distinct fields around the conductor - - the
electrostatic (capacitive) field and the magnetic
(inductive) field. Both are capable of inducing
longitudinal voltages in adjacent conductors, and both
increase in proportion to the power and frequency of the
current from which they result. They differ greatly,
however, in how they affect nearby circuits. The voltage
resulting from magnetic induction varies inversely-with
the impedance of the line. That is, the higher the line
impedance, the less voltage that can be induced by a
magnetic field. Capacitively coupled voltage, on the
other hand, increases in direct proportion to line
impedance-- the higher the impedance, the greater the
capacitive coupling. By means of a simple test, it is
possible to identify the coupling between two lines, as
shown in Figure 3-8. Since induced voltages are
inversely proportional to line impedance, the voltage
coupled from pair A into pair B (Figure 3-8a) will
increase as the impedance is lowered (i.e., shorted).
Conversely, since capacitively coupled voltages are
directly proportional to impedance, the coupled voltage
in Figure 3-8b would increase as the impedance is
increased (i.e., open circuited). Both tests in Figure 3-8
should be performed to correlate the result.
3-64. MEASUREMENTS IN DBC.
3-65. The term dBC means dB Collins and is defined
as
the interfering signal can be read directly off the
3-11
Section III Model 3555B
Figure 3-8. Simple Test for Inductive and Capacitive Coupling
0dBC = 0.775V across any impedance as read on an
-hp- Model 400D AC Vacuum Tube Voltmeter. Thus,
the dBC is strictly a relative term.
3-66. Measurements can easily be made in dBC. by
utilizing the Model 3555B Telephone Test Meter. To
make these measurements, set FUNCTION to 600 and
the INPUT switch to TMS BRDG. Any termination
required other than 600 ohms must be provided
externally and connected across the two binding posts T
and R. Termination can also be made using a patch
cord and any one of the other INPUT jacks since all
INPUT jacks are connected in parallel. If a 600 ohm
termination is to be used, the internal termination can be
utilized by placing the INPUT switch to the TMS TERM
position.
3-67. MEASUREMENT PROCEDURES.
3-68. Tables 3-3 through 3-8 list the step by step
procedures for measuring levels and noise balance,
recorder calibration and transmission loss using the
3555B. For a more detailed discussion on level and
noise measurements refer to paragraphs 3-12 through
3-47.
3-69. 150 BAL CONVERSION.
3-70. The 3555B comes equipped with all the
necessary parts for converting the 135 BAL function to a
150 BAL function. The following is a simplified
procedure for making the modification.
a. Remove the set from the case and remove
the FUNCTION board. Clip the shorting
wire from across A1R17 (see Figure 7-2)
and reinstall the FUNCTION board. Leave
the set out of the case.
b. Set the 3555B controls as follows:
RANGE..........................................0dBm
FUNCTION................................135 BAL
INPUT ..................................TMS TERM
c. Remove the 150 BAL decal from the
envelope supplied with the set. Remove
the backing from the decal and place it
over the 135 BAL function pushbutton.
d. Connect a 150 ohm balanced source to the
input of the 3555B at a level of 0dBm
(387mV rms) at a frequency of 1kHz. Turn
the 3555B ON and adjust A3R24 (Figure 7-
3) for 0dBm indication on the 3555B meter.
e. Reinstall the set in its case.
3-12
Model 3555B Section III
Table 3-3. Level Measurement
STEP PROCEDURE
1. Turn the 3555B/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 before attempting to make any
measurements. The battery test operates for
internal battery, office battery or ac power
source.
2. Select either TMS BRDG or TMS TERM,
depending on the measurement being made.
The weighting filters are not in the circuit at
this time.
3. Select the impedance (FUNCTION
pushbutton) to match the circuit to be tested.
Select either 900 BAL or 600 BAL (VF/Nm) for
frequencies between 20Hz and 20kHz. Select
600 BAL or 135 BAL (CARRIER) for balanced
measurements between 1 kHz and 600kHz.
Select 75 UNBAL for 75 ohm unbalanced
measurements between 30Hz and 3MHz.
4. Set the RANGE switch to +30dBm. Set the
RESPONSE switch to DAMP.
5. Connect the set to the line using a suitable
patch cord. For balanced measurements use
a cord having a 309 or 310 single plug, a 241
dual plug or banana plugs, bare wires or clip
leads. For unbalanced carrier measurements
(75 ohm only) use a cord having a 358 plug.
NOTE
Carrier measurements are
limited to the -50dBm RANGE
thru the +10dBm RANGE.
6. Down range the RANGE switch for an onscale indication. Level is equal to the
algebraic sum of the black RANGE setting
plus the black meter scale indication.
Table 3-4. Noise Metallic Measurements
STEP PROCEDURE
1. Turn the 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 on
internal battery, office battery or ac power
source.
2. Select either NOISE TERM or NOISE BRDG,
depending on the measurement being made.
3. Select the impedance to match the circuit to
be tested using the FUNCTION pushbuttons.
The 900 BAL VF/Nm pushbuttons only should
be used for noise metallic measurements in
the frequency range of 20Hz to 20kHz. The
HOLD function can be used in NOISE TERM
if desired.
4. Select the appropriate weighting filters using
the NOISE WTG switch.
5. Set the RANGE switch to 110dBrn.
6. Connect the set to the circuit to be tested
using a suitable patch cord and down range
for an on-scale indication.
7. Observe the meter fluctuations for two or
three minutes and take a reading where the
meter pointer appears to be most of the time,
disregarding any occasional peaks.
NOTE
For rapidly fluctuating noises
such as atmospheric noise or
switching noise, operate the
RESPONSE switch to DAMP
and read the level of the most
frequently occurring peaks.
8. Noise level is equal to the sum of the blue
RANGE switch setting in dBrn and the
indication on the blue meter scale in dBrn.
EXAMPLES:
RANGE = -50dBm
METER = +1dBm
LEVEL = -49dBm
RANGE = +20dBm
METER = -4dBm
LEVEL = +16dBm
EXAMPLE:
RANGE = 40dBrn
METER = +5dBrn
NOISE LEVEL = +45dBrn
3-13
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