Middleton W.M. (ed.) Reference Data for Engineers: Radio, Electronics, Computer and Communications

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1-160

TABLE

17.

INTERNET

TIME

PROTOCOLS

Protocol Name Document Format Port Assignments

Time Protocol RFC-868

Daytime Protocol RFC-867

Unformatted 32-bit binary number contains time

UTC sec-

Exact format not specified

standard. Only requirement is that

Port 37 tcp/ip, udplip

Port 13 tcphp, udp/ip

onds since January 1,1900.

the time code

sent as ASCII characters.

Network Time RFC-1305 The server provides a data packet with a 64-bit timestamp con- Port

Protocol (NTP)

taining the time

UTC seconds since

January

1900

with

a resolution

200

ps.

NTP provides accuracy of 1

ms.

The

client software runs continuously and gets periodic

updates from the server.

The data packet sent by the server is the same as NTP, but the

client software does less processing and provides less

Simple Network

Time Protocol

(SNTP) accuracy.

RFC-1769

Port

23 udplip

ibrate the path using the

loop-back

method. Each time

the OTM is returned, the server measures the round-

trip path delay and divides this quantity by

to esti-

mate the one-way path delay. This path calibration

reduces the uncertainty to

ms.

Global Positioning

System

(GPShGPS,

well

known as a versatile, global tool for positioning, has

also become a primary system for distributing time

and frequency.

GPS

receivers are fixtures in telecom-

munication networks and in calibration and testing

laboratories. They make

possible to synchronize

clocks and calibrate and control oscillators in any

facility that can place an antenna outdoors for line-of-

sight reception of the

GPS

satellites.

The

GPS

satellites are controlled and operated by

the United States Department of Defense (USDOD).

The constellation includes at least

24 satellites that

orbit the earth at a height of

20 200

in six fixed

planes inclined

55"

from the equator. The orbital

period is

m, which means that a satellite will

orbit the earth twice per day.

processing signals

received from the satellites, a

GPS

receiver can deter-

mine its position with an uncertainty of

The

GPS

satellites broadcast on two carrier frequen-

cies:

575.42

MHz and

227.6

MHz.

Each satellite broadcasts a spread-spectrum waveform,

called

pseudo-random

noise

(PFW)

code

and

L2,

and each satellite

identified by the

PRN

code it

transmits. There are two types of

PRN

codes. The first

type is a coarse acquisition (CIA) code with a chip rate

023

chips per millisecond. The second type is a

precision

(P)

code with a chip rate of

10 230

chips per

millisecond. The CIA code is broadcast on

L1,

and the

code is broadcast on both

and

L2.

GPS

reception

is line-of-sight, which means that the antenna must

have a clear view of the sky.

a clear sky view

available, the signals can be received nearly anywhere

on earth.

Each satellite carries either rubidium or cesium

oscillators, or a combination of both. The on-board

oscillators provide the reference for both the carrier

and code broadcasts. They

are

steered

from

USDOD

ground stations and are referenced to Coordinated

Universal Time (UTC) maintained by the United

States Naval Observatory

(USNO).

By mutual agree-

ment UTC(USN0) and UTC(N1ST)

are

maintained

within

100

each other, and the frequenc differ-

ence between the two time scales is

lo-'

GPS Measurement Techniques:

GPS

measurements

can be divided into two categories: one-way and com-

mon-view. Most

GPS

measurements are one-way mea-

surements, based on direct reception of the

GPS

signals. Common-view measurements require more

effort, including a data exchange between two receiv-

ers and postprocessing of the measurement data. For

this reason, they are usually reserved for international

comparisons between metrology laboratories when the

measurement uncertainties must be as small as possi-

ble. Table 18 compares the

GPS

measurement tech-

niques.

One-way GPS:

The one-way

GPS

technique uses

the signals obtained from a

GPS

receiver as a time and

frequency reference. The

GPS

signals are used in real

time, and no postprocessing of the measurement

results is required. The signal is normally used either

TABLE

18.

TYPICAL UNCERTM

GPS

MEASUREMENT

TECHNIQUES

Timing Frequency

Uncertainty, Uncertainty,

Technique 24

One-way

20 ns

10-l~

Single-Channel

ZlO

10-l~

Multichannel

10-l~

Common-View

SPECTRUM MANAGEMENT

1-161

to synchronize an on-time pulse or to calibrate a fre-

quency source.

Since the GPS satellites transmit signals that

are

steered to agree with UTC, the long-term accuracy

GPS receiver has always been excellent. The perfor-

mance of C/A code receivers became even better

May

2000

(MJD 51666) when the USDOD set

selective availability (SA) to zero. SA is a USDOD

directive that can be used to intentionally introduce

noise

the GPS signal to reduce its positioning and

timing accuracy. Fig. 14 is a phase plot showing data

from a typical GPS receiver, recorded in the days

immediately before and after SA was set to zero.

The data points shown

Fig. 14

are

10-minute

averages of the received signal obtained by comparing

the

pps output from a typical GPS timing receiver to

UTC(N1ST) using a time interval counter. The phase

plot shows that the GPS broadcasts are tightly con-

trolled. The peak-to-peak variation in the received sig-

nal is

at one day after

was set to

This

leads to excellent long-term accuracy and stability. The

Allan deviation,

CX,,(T),

plot in Fig. 15 shows that the

stability of the receiver is near

Common-View

GPS

Measurements:

The common-

view method is a simple but elegant way to compare

two clocks or oscillators located in different places.

Unlike one-way measurements that compare a clock or

oscillator to GPS,

common-view measurement com-

pares two clocks or oscillators to each other.

Fig. 16 shows how the common-view technique

works. A GPS satellite

(S)

serves as a single reference

transmitter. The two clocks or oscillators being com-

pared (A and

are measured against two GPS receiv-

ers. The satellite is

common view of both receivers,

and

its signals are simultaneously received by both.

day.

-10

-30

-50

Frequency Stability

GPS

Receiver

lff

lo'

Averaging

Time.

Seconds

Fig.

15.

Frequency stability

(Allan

deviation) of GPS receiver

after

was set to

Each receiver compares the received signal to its local

clock and records the data. Receiver A receives the sig-

nal

over the path

rsA

and compares the reference to the

local clock (S-Clock A). Receiver

receives the sig-

nal over the path

T~~

and records (S-Clock

B).

The

two receivers then exchange and difference the data.

Common-view directly compares two time and

frequency standards. Errors from the two paths

(rSA

and

T~~)

that are common to the reference cancel

out, including the performance of the satellite clock.

The final measurement result is (Clock A-Clock

The common-view technique has long been used for

international comparisons of time and frequency

stan-

dards. The international time scales-International

Atomic Time (TAI) and Coordinated Universal Time

(UTC)-are created by averaging data collected from

B)-

(TSA-TSB).

GPS

before and after SA Deactivation

minute averages

all satellites in

view

-70

51663

664 51665 51666 51 667 51668

MJD

Fig.

14.

Phase

plot

showing GPS

performance

before and after SA was set

1-1

REFERENCE

DATA

FOR ENGINEERS

Fig.

16.

The common-view measurement technique.

more than 200 atomic clocks located in more than 40

laboratories. Most of these data are collected using

common-view GPS measurements. Once the data

are

sent to the BIPM, the TAI and UTC time scales

are

computed using a weighted average of all the oscilla-

tors. The stability of TAI and UTC is currently about 1

part in

10'~

over a period of a few weeks.

Common-view measurements can

single channel

multichannel. The BIPM has conventions for

recording the data used in both types of measurements.

However, it is not necessary

use the BIPM format to

make common-view measurements. Any data format

can

used

all participants in a common-view com-

parison record and process their data in the same way.

BIBLIOGRAPHY

References

Allan, D. W., Ashby, N., and Hodge, C. C. (1997).

The

Science of Timekeeping.

Hewlett-Packard Applica-

tion Note 1289, United States.

Hackman, C., and Sullivan, D. B.,

Eds.

(1996).

Time and

Frequency Measurement.

American Association of

Physics Teachers, College Pxk, Maryland.

IEEE Standards Coordinating Committee 27. (1999).

IEEE Standard Definitions of Physical Quantities

for Fundamental Frequency and Time Metrol-

og)LRandom Instabilities.

Institute of Electrical

and Electronics Engineers, New York.

ITU

Radiocommunication Study Group 7. (1997).

Selec-

tion and Use

Precise Frequency and Time

Sys-

tems.

International Telecommunication Union,

Geneva, Switzerland.

Jesperson,

J.,

and Fitz-Randolph, J. (1999).

From Sun-

dials to Atomic Clocks: Understanding Time and

Frequency.

NIST Monograph

155,

US Govem-

ment Printing Office, Washington,

DC.

Levine, J. (1999). Introduction to time and frequency

metrology.

Review of Scientifrc Instruments

70,

Seidelmann, P.

K.,

Ed.

(1992).

Explanatory Supplement

to the Astronomical Almanac.

University Science

Books, Mill Valley, California.

Sullivan, D.

B.,

Allan, D. W., Howe, D. A., and Walls,

L.,

Eds.

(1990).

Characterization of Clock and

Oscillators.

NIST Technical Note 1337, US Gov-

ernment Printing Office, Washington,

DC.

Vig, J. R. (1992).

Introduction to Quartz Frequency

Standards.

United States Army Research and

Development Technical Report SLCET-TR-92-1.

2567-2596.

Spectrum Management

For international technical standards, see the

Rec-

ommendations

the International Telecommunication

Union,

ITU-R Publications, latest edition, available

from the International Telecommunication Union,

Geneva, Switzerland.

All ITU-R Recommendations in force at the end

the Radiocommunication Assembly (RA-97) (24

October 1997) are published in the 1997 Volumes

(except

for

the few "old" Recommendations published

in the 1992

Series Fascicule and in Volumes I11 and

of the CCIR

XVIIth

Plenary Assembly (Dussel-

dorf, 1990)). ITU-R Recommendations

are

divided

into Series according to the subject areas covered, as

follows:

SM SERIES

(SG 1)Spectrum Management

SERIES

(SG 1)Interservice Sharing and Com-

P SERIES-Part

(SG 3)Radiowave Propagation

P SERIES-Part

(SG

3)Radiowave Propagation

SERIES

(SG 4)Fixed-Satellite Service

SNG

SERIES

(SG 4)Satellite News Gathering

SERIES

(SG

7)Time Signals and Frequency

SERIES

(SG

7)Space Applications and Meteor-

RA SERIES

(SG

7)Radioastronomy

SERIES-Part

(SG 8)Land Mobile Service

M SERIES-Part

(SG

@International Mobile

patibility

Standards Emissions

ology

Excluding WIT-2000

Telecommunications-2000 (IMT-2000)

1-1

SERIES-Part

(SG 8)Maritime Mobile Ser-

vice and Aeronautical Mobile Service

SERIES-Part

(SG 8)Radiodetermination

Service

SERIES-Part

(SG 8)Mobile-Satellite Ser-

vices and Radiodetermination-Satellite Service

SERIES-Part

(SG 8)Amateur Service and

Amateur-Satellite Service

SERIES-Part

(SG 9)Fixed Service-

Radio-Relay Systems

SERIES-Part

(SG 9)Fixed Service-

Frequency Sharing Aspects

SERIES-Part

(SG 9)Fixed Service-

HF Systems

SERIES

(SG 4-9)Frequency Sharing between

the Fixed-Satellite Service and the Fixed Service

BS SERIES

(SG 10)Broadcasting Service (Sound)

Rec.

ITU-R

BS.705-1

and

Rec. ITU-R

BS.1195HF

Transmitting and Receiving Antennas Character-

istics and Diagrams-Transmitting Antenna

Characteristics at VHF and UHF

sion)

Service (Sound and Television)

Recording

BT SERIES

(SG 11)Broadcasting Service (Televi-

BO SERIES

(SG 10-1

1S)Broadcasting-Satellite

BR SERIES

(SG 10-1 1R)Sound and Television

SERIES

(CCV)Vocabulary and Related Subjects

Communications Act

1934, as amended.

Con-

gress.

“Manual

Regulations and Procedures for Federal

Radio Frequency Management.” Washington, DC:

National Telecommunications and Information

Administration, updated annually.

Title 47, Code of Federal Regulations, “Federal Com-

munications Commission,” four volumes. Wash-

ington, DC: Office of the Federal Register, updated

“Spectrum Management.” Appendix A,

NTIA

TELE-

COM

2000:

Charting the Course

for

New

Cen-

tury,

NTIA Special Publication 88-21. Washington,

DC: National Telecommunications and Informa-

tion Administration, October 1988.

Matos, F.

Spectrum Management and Engineering.

New York: IEEE Press, 1985. (Reprints of 51

papers on various international and domestic spec-

trum

management topics plus additional material

on legal and regulatory matters, and spectrum

management tools and methods.)

“U.S.

Spectrum Management Policy: Agenda for the

Future,” NTIA Special Publication 91-23. Wash-

ington, DC: National Telecommunications and

Information Administration, February 199

Nunno, Richard M. “Radiofrequency Spectrum Man-

agement: Background, Status,

and

Current Issues,”

CRS Report for Congress RL30829. Washington,

annually.

DC: Congressional Research Service, January 30,

200

Information from the Internet

Radio frequency spectrum management information

available

the Internet. The telecommunications

regulatory administrations of many countries have

active websites that should be consulted when dealing

with spectrum issues involving those nations. Three

extensively used sites are:

National Telecommunications and Information

Administration at www.ntia.doc.gov

2. Federal Communications Commission at

3. International Telecommunication Union at

www. fcc.gov

www.itu.int

Spectrum Management

Tra

Radio frequency spectrum management training is

1. George Washington University, Center for Profes-

available from two sources:

sional Development, Washington, DC.

www.cpd.gwu.edu

2. For students from developing nations: United

States Telecommunications Training Institute,

Washington, DC. www.ustti.org

Time and Frequency

Blair, B.

E.,

Ed. “Time and Frequency: Theory and

Fundamentals,” NBS Monograph 140. Boulder,

CO: National Bureau of Standards, Dept. of Com-

merce, 1974.

Technical standards published as reports and recom-

mendations of the International Radio Consultative

Committee (CCIR), International Telecommunica-

tion Union (ITU), Geneva, Switzerland. Reports

and recommendations are revised periodically, and

it is best to refer to the latest version. In particular:

“Performance of Standard-Frequency Genera-

tors,” Report 346-6 or later version, Reports of

the CCIR, 1990 or later, Annex to Volume VII,

Standard Frequencies and Time Signals.

“Standard-Frequency and Time-Signal Emis-

sions,” Recommendation 4604 or later version,

Recommendations of the CCIR, 1990 or later,

Volume VII, Standard Frequencies and Time

Signals.

Beehler, R.

E.,

and Lombardi,

A. “NIST Time and

Frequency Services,” NIST Special Publication

432. Boulder, CO: Dept.

Commerce, National

Institute of Standards and Technology, June 1991.

International

Telephony

Recommendations

Revised by

Douglass

Crombie

and

Dorothy

Cerni

International Standards

2-3

Recommendations

the CCITT

Recommendations of the CCIR

Zero-Relative-Level Points and Relative Levels

2-3

Psophometric Noise and Power

2-4

Psophometric Weighting for Commercial Telephone Circuits

Psophometric Weighting Factor

Psophometric Power

Conventional Telephone Signal

2-5

Telephone Circuit Loading

2-5

Nominal Mean Power During Busy Hour

Conventional Load

Power Levels

2-6

Maximum

Power Level

for

Signaling Pulses

Private Telegraph Transmission on a Rented International

Circuit, With Alternative Private Telephone Service

Simultaneous Communication by Telephony and Telegraphy

on a Telephone Circuit

Phototelegraphy Transmissions Over Telephone Circuits That

Are Entirely 4-Wire Between Phototelegraph Stations

Power Levels for Data Transmission Over Telephone Circuits

2-2

REFERENCE

DATA

FOR ENGINEERS

Hypothetical Reference Circuits

2-7

General Definitions (G.212)

Important Hypothetical Reference Circuits Defined by

CCITT and CCIR

Telephone Circuit Characteristics

2-9

Impedance of International and National Trunks

One-way Propagation Time

Group Delay Distortion

Attenuation Distortion in Worldwide Chain

Variation

Transmission Loss With Time

Linear Cross Talk

Frequency Accuracy of Virtual Carrier Frequencies on an

International Circuit

Circuit Noise Objectives

2-11

Reference Circuits

Kilometers in Length

Noise Characteristics for 252-Kilometer Hypothetical

Noise Characteristics for Long Circuits Not More Than 252

Noise Characteristics for International Circuits More Than 252

Noise in Actual Circuits

Designed Objectives for Noise Produced by Modulating

Equipments

CCITT and Telegraphy

2-13

Numbering

CCITT and Telephony

2-13

International Country Codes

Telephone Signaling

2-13

Supervisory or Line Signals

Ringdown Signals

Tones

Alternative Routing

2-3

INTERNATIONAL STANDARDS

Administrations and operating companies throughout

the world carry on studies of technical and other

problems related to the interworking of their respective

national telecommunication systems to provide a world-

wide telecommunications network. Two international

committees exist for this purpose: The International

Telegraph and Telephone Consultative Committee

(CCITT), and the International Radio Consultative

Committee (CCIR). They operate under the auspices of

the International Telecommunication Union (ITU).

They promulgate their decisions in the form of Recom-

mendations, which are published by the ITU. General-

ly, these Recommendations cover features of interna-

tional circuits, but where essential, they deal with

relevant characteristics of the national systems which

may form part of international connections. This com-

pendium collects, in condensed form, major Recom-

mendations dealing with telephone, telegraph, and

data-transmission circuits and equipment.

Recommendations

the

CCITT

The CCITT develops new Recommendations, and

updates existing ones, through the activities of Study

Groups, whose reports are acted on at Plenary Assem-

blies, which meet at intervals of three or four years. The

resulting Recommendations of the Second Plenary

Assembly, New Delhi, 1960, were published by the

ITU in a number of volumes, called collectively the Red

Book. The subsequent study periods culminated in the

Third Plenary Assembly, Geneva, 1964 (Blue Book);

the Fourth Plenary Assembly, Mar del Plata, 1968

(White Book); the fifth Plenary Assembly, Geneva,

1972 (Green Book); the Sixth Plenary Assembly,

Geneva, 1976 (Orange Book); and the Seventh Plenary

Assembly, Geneva, 1980 (Yellow Book). This compen-

dium refers to Yellow Book Recommendations, desig-

nated thus: (G. lo]), (H.31),

(V.2),

etc.

Recommendations

the

CCIR

The CCIR also functions with Study Groups and

Plenary Assemblies. The Eleventh Plenary Assembly

was held at

Oslo

in 1966, the Twelfth Plenary Assembly

at New Delhi in

1970,

the Thirteenth Plenary Assembly

at Geneva in 1974, the Fourteenth Plenary Assembly at

Kyoto in 1978, and the Fifteenth Plenary Assembly at

Geneva

1982. After each Plenary Assembly, the ITU

publishes volumes which contain the currently accepted

Recommendations, including such Recommendations

of the Plenary Assemblies at London (1953), Warsaw

(1956), Los Angeles (1959), and Geneva (1963) which

are still in effect. No color coding is used. This

compendium deals with those Recommendations which

treat point-to-point radio relay systems. A purpose of

those Recommendations is to make the performance

such systems compatible with metallic line systems

which follow the CCITT Recommendations. Referenc-

es to the CCIR Recommendations are made thus:

(CCIR, 39

1).

NOTE: This chapter is primarily concerned with

telephony, but additional material is included in

chapter

38,

Common Carrier Transmission. For

more information

data communications, the

reader is referred to chapter

26,

Computer

Communications Networks.

ZERO-RELATIVE-LEVEL

POINTS AND RELATIVE

LEVELS

Many CCITT and CCIR Recommendations specify

signal or noise levels at “a point of zero relative level,”

or in dBmO or pWp0, etc., where

“0”

(zero) stands for

“measured at or referred to a point of zero relative

level.

’ ’

(A)

In two-wire switching systems, the sending-end

terminals of a long-distance circuit have long been

considered to be at a point of zero relative level. The

relative levels of all other points are calculated from this

reference point, as the algebraic sum of all transmission

losses and gains from it to the point in question. Any

point in a circuit with the same relative level as the

sending terminals is a point of zero relative level, which

may be written

dBr

(dB

relative level). The American

term for

relative level

transmission level.

Thus:

‘

‘Zero-transmission-level point” (OTLP).

For convenience in comparing circuit noise perform-

ance, it is customary to convert absolute noise measure-

ments made at the receiving ends

circuits having

various relative levels, to absolute power levels at a

zero-relative-level point. For example,

-50

dBmp of

noise at a -7-dBr point would be reported as -43

dBmOp. Signaling-tone levels are similarly expressed.

For example, a tone introduced at a -3.5-dBr point

with an absolute power level of -18.5 dBm may be

referred to as a

15-dBmO signal. The latter designa-

tion would apply to such a tone no matter where it

appeared; the

“0”

denotes that its level is referred to a

point of zero relative level. (Refer to Table

Statistics of speech power, requirements for linearity

and limiting, system loading factors,

cross

talk, and

noise have become well known in terms of their values

at points of zero relative level. The proper performance

of voice repeaters, carrier terminal and line equipment,

radio relay systems, etc., depends on adherence to the

relative levels for which they were designed. Many

relative levels associated with such equipment have been

standardized.

(B)

In four-wire switching systems, it is often con-

sidered desirable to handle speech and signaling at

lower values of absolute power through the switching

2-4

REFERENCE DATA FOR ENGINEERS

TABLE

RELATIVE LEVELS, PLUS LEVELS

ABSOLUTE

AND

REFERRED POWER,

FOR

2-WIRE CIRCUIT

Sending

Circuit

Loss:

dB Receiving

Point

Direction+ Point

2-Wire Circuit

Relative levels,

transmission levels

dBr

-5

dBr

“Milliwatt” test tone

At any point

Signaling tone

At any point

dBm

dBmO

-5

dBm absolute power

dBmO referred power

dBm absolute power

dBmO referred power

dBm

dBmO

Circuit noise, picked up along circuit

Circuit noise, referred to 0-dBr point

-65 dBmp absolute power

-60 dBmOp referred power

equipment than is customary in two-wire systems. In

1964,

the CCITT adopted a relative level of

-3.5

dBr

for the sending end of a four-wire circuit, at the

“virtual” switching points. These are theoretical

points; their exact location depends on national prac-

tice, and the CCITT considers it unnecessary to define

them. (In the American commercial system, -2 dBr is

widely used.)

(G.

101,

Section B)

Therefore, to ensure that carrier and other transmis-

sion equipment will be subjected to the same absolute

speech and signaling power levels as in two-wire sys-

tems, determination of relative levels in four-wire

circuits must take into account the relative level of the

virtual switching points. In a four-wire circuit, there

may be no actual point of zero relative level. Neverthe-

less, standards will continue to refer many requirements

a zero relative point. (Refer to Table 2.)

Currently, many transmission measurements are

made with a standard

800-

or 1000-hertz test tone, with

an absolute power of

milliwatt at a zero-relative-level

point: a power of

dBrnO. The actual level applied is

adjusted to the relative level of the sending point. The

test-tone level in dBm will be numerically equal to the

relative level in dBr at any point in the circuit, but it is

not proper to express

relative

levels in dBm, since dBm

represents absolute power levels. If the standard-test-

tone power is ever changed to another value, such as

-10

dBmO, as has been tentatively proposed, the

distinction between relative levels and test-tone levels

will be more apparent.

PSOPHOMETRIC NOISE AND

POWER

The CCITT calls a noise measuring set a “psophom-

eter.”

psophometer includes

device for measuring

power through a weighting network. For measurements

on commercial telephone circuits, a weighting charac-

teristic is used which results in the objective instrument

TABLE 2. RELATIVE LEVELS, PLUS LEVELS

ABSOLUTE

AND

REFERRED POWER,

FOR

ONE DIRECTION

4-WIRE CIRCUIT

Sending

Circuit

Loss:

5 dB Receiving

Point Direction- Point

-u

One

side of 4-Wire Circuit

Relative levels, or transmission levels

“Milliwatt” test tone

At any point

Signaling tone

At any point

Circuit noise, picked up along circuit

3.5 dBr

3.5 dBm

dBmO

-13.5 dBm

-10 dBmO

8.5 dBr

8.5 dBm absolute power

-18.5 dBm absolute power

10 dBmO referred power

-68.5 dBmp absolute power

dBmO referred power

Circuit noise, referred to 0-dBr point

-60 dBmOp referred power

INTERNATIONAL TELEPHONY RECOMMENDATrONS

2-5

measurements approximately paralleling the results

subjective tests with human observers using modern

telephone sets. The CCITT weighting characteristic for

commercial circuits is nominally identical with the

American

A line weighting. Psophometric noise

power may be expressed in dBmO “psophometrically

weighted,” or dBmOp. -The conventional conversion

equation used between dBmOp and dBaO

(FIA)

dBmOp

dBaO

Psophometric Weighting for

Commercial Telephone Circuits

Frequency Level Frequency Level

(hertz)

(dB)

(hertz)

(dB)

100

-41

1350 -0.65

150 -29.0 1500

1.30

200 -21.0

1750 -2.22

250 -15.0 2000 -3.00

300

10.6

2250 -3.60

400 -6.3 2500 -4.20

500

-3.6

2750 -4.87

600 -2.0 3000

-5.60

700

-0.9

3500 -8.5

800

0.0

4000

15.0

900 +0.6

4200 -18.7

1000

f1.0

4500 -25.0

1100

+0.6

4700 -29.4

1200

0.0

5000 -36.0

(Extracted from

G.223,

which gives weighting for

frequencies.)

Psophometric Weighting Factor

If uniform-spectrum random noise is measured in

3.1

-kilohertz band with

flat attenuation/frequency

characteristic, the noise level must be reduced by

2.5

decibels to obtain the psophometric power level. For

another bandwidth

the weighting factor will be equal

2.5

loglo(B/3.1) decibels

When

4 kilohertz, for example, this gives

weighting factor of

3.6

decibels.

(G.223)

Psophometric Power

Where power addition of noise can be assumed, it has

been found convenient for calculations and design of

international circuits to use the concept of “psopho-

metric power.

’ ’

psophometric power

(psophometric ~oltage)~/600

(psophometric e1nf)~/(4

600)

A convenient unit is the picowatt (pW)

that

watt,

psophornetric power in pW

(psophometric emf in 1nV)~/0.0024

(G.212)

CONVENTIONAL TELEPHONE

SIGNAL

For the calculation or measurement of cross-talk

noise between adjacent channels, of the balance return

loss for echo, and generally speaking, when it is desired

to simulate the speech currents transmitted by

tele-

phone channel, the CCITT recommends the use

conventional telephone signal. This signal may be

produced by passing the output

generator of a

uniform-spectrum random noise signal (“white noise”)

through

weighting network with

characteristic

shown in Fig.

The amount of this signal that appears

in another circuit because of cross talk, etc., is mea-

sured with

psophometer or weighted-noise measuring

set, with standard psophornetric weighting for commer-

cial telephone circuits.

(G.227)

TELEPHONE CIRCUIT

Nominal Mean Power During

Busy

Hour

simplify calculations when designing carrier sys-

tems

cables or radio links, the CCITT has adopted

conventional

value to represent the

mean absolute

power level,

point of zero relative level, of the

speech-plus-signaling currents, etc., transmitted over

telephone channel in one direction of transmission

during the busy hour, which is

-15

dBm

(-1.73

nepers) (mean power

1.6

microwatts); this is the

mean with time and the mean for a large batch of

circuits. This total mean power of about

microwatts

is conventionally distributed

follows (nominal mean

power):

microwatts,

all

signaling and tones;

microwatts, to include speech currents (including ech-

oes), carrier leak, and telegraph signals, based

speech activity factor of

0.25

for one direction of

telephone channel. No account is taken of pilot signals,

which are assumed to be an integral part of the carrier

system, not affecting telephone channel power. ((3.223,

Section 1)

Conventional Load

It will be assumed for the calculation of intermodula-

tion noise below the overload point that the multiplex

signal during the busy hour can be represented by a