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PUBLICATIONS

Electrical Performance Tests for

Audio Distortion Analyzers

O.B. Laug, G.N. Stenbakken, and T.F. Leedy

U.S. DEPARTMENT OF COMMERCE

National Bureau of Standards

Gaithersburg, MD 20899

July 1985

Final Report

Issued November 1985

-QC

100

• U56

85-3269

1985

“'red for: “"Army Communications Electronics Command

Monmouth, New Jersey 07703

NBS RESEAK31 information CENTEB

NBSIR 85-3269

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ELECTRICAL PERFORMANCE TESTS FOR

AUDIO DISTORTION ANALYZERS

O.B. Laug, G.N. Stenbakken, and T.F. Leedy

U S. DEPARTMENT OF COMMERCE

National Bureau of Standards

Gaithersburg, MD 20899

July 1 985

Final Report

Issued November 1985

Prepared for: U.S. Army Communications Electronics Command

Fort Monmouth, New Jersey 07703

U.S. DEPARTMENT OF COMMERCE, Malcolm Baldrige, Secretary

NATIONAL BUREAU OF STANDARDS. Ernest Ambler, Director
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TABLE OF CONTENTS

Page

List of Figures iv

List of Tables . v

Abstract 1

1. Introduction 1

2. Background 2

3. Audio Distortion Analyzer Applications & Principles 3

4. Distortion Analyzer Performance Measurements 9

4.1 Input/Output Characteristics . 10

4.1.1 Input Impedance 10

4.1.2 Input Common-Mode Rejection Ratio (CMRR) ........ 14

4.1.3 Input Protection 19

4.1.4 Monitor Output Impedance . ; 19

4.1.5 Monitor Output Frequency Response 22

4.1.6 Monitor Output Linearity (Absence of Clipping) 23

4.2 Voltmeter Mode 23

4.2.1 Voltmeter Accuracy and Range 23

4.2.2 Bandwidth 24

4.3 Distortion Measurements 25

4.3.1 Two Sine Wave Test 26

4.3.2 3:1 Crest Factor Signal Test 30

4.3.3 SINAD Test 40

4.3.4 Residual Distortion and Noise 42

% 4.4 Filter Character! sties 45

4.4.1 High Pass/Low Pass Filter Measurements 45

5. References 49

Appendix A A-1

Appendix B B-1

Appendix C C-1

Appendix D D-1

Appendix E E-1

Appendix F F-l

i i i
List of Figures

Page

Figure 1 Block diagram of a harmonic distortion measurement. The

basic distortion analyzer has a tunable notch filter to remove the fundamental frequency component of the signal

and a detector to measure the remaining signal 5

Figure 2 Block diagram of the essential elements contained in a modern audio distortion analyzer. 8

Figure 3 Equivalent circuit for determing input impedance 11

Figure 4 Test setup for measuring the common-mode rejection ratio

of an audio distortion analyzer (preferred method) 15

Figure 5 An alternate method of measuring the common-mode

rejection ratio of an audio distortion analyzer 18

Figure 6 Equivalent circuits for determining output resistance 20

Figure 7 Test setup for measuring distortion accuracy with the

sine wave signals 27

Figure 8 Test setup for measuring distortion accuracy with

signals that have a 3:1 crest factor 29

• Figure 9 Waveform of 3:1 crest factor signal using 9th harmonic

pulses with amplitudes of 1.86 times the fundamental

amplitude 34

Figure 10 Waveform of 3:1 crest factor signal using 19th harmonic

pulses with amplitudes of 0.826 times the fundamental

amplitude 35

Figure 11 Magnitude spectrum of 3:1 crest factor signal using

9th harmonic pulses 36

Figure 12 Magnitude spectrum of 3:1 crest factor signal using

19th harmonic pulses 37

Figure 13 Test setup for measuuring 5INAD accuracy 39

Figure 14 Test setup for measuring residual distortion and noise. ... 41

Figure 15 Test setup for measuring residual distortion and noise

at input levels above 10 volts rms 43

Figure 16 Test setup for measuring the quality of the 1 ow-di stortion

oscillator 44

Figure 17 Typical Bode plots of high and low-pass filters

i V

46
List of Tables

Page

Table 1 Typical AC Calibration Accuracy Specification 24

Table 2 Magnitude for the 9th Harmonic Pulse 31

Table 3 Magnitude for the 19th Harmonic Pulse 32

Table 4 Crest Factors Resulting from Various Combinations

of Amplitude and Harmonic Number 32

Table 5 Error Resulting From Using a Limited Number of

Harmonics to Calculate THO 33

V

ELECTRICAL PERFORMANCE TESTS FOR AUDIO DISTORTION ANALYZERS

0. B. Laug, G. N. Stenbakken, and T. F. Leedy

Abstract

Electrical performance test procedures for audio distortion analyzers

were developed by the National Bureau of Standards for the U. S. Army

Communications-Electronics Command. The report provides detailed,

step-by-step test procedures that are based on specifications supplied by the

Army for purposes of evaluating audio distortion analyzer bid samples.

Examples of data sheets and tables are also provided for recording interim and

final results.

This report discusses the philosophy of each measurement procedure with a view toward providing an understanding of the basic metrology required to

perform the measurements. In addition, the sources of measurement error are discussed. The primary applications and basic principles of modern audio

distortion analyzers are also presented.

Key Words: audio distortion analyzer; distortion analyzer; distortion;

distortion ^specification; and test procedures.

1. INTRODUCTION

This report describes test procedures that were developed by the National

Bureau of Standards (NBS) for the U. S. Army Communications-Electronics

Command (CECOM) for testing the electrical performance of audio distortion

analyzers. The test procedures are based on specifications supplied by CECOM,

and will be used by the Army in their Test Measurement and Diagnostic

Equipment (TMDE) Modernization Program to evaluate audio distortion analyzer

bid samples. The report focuses only on the electrical performance test

procedures that can be performed without access to the interior of the

instrument under test.

The test procedures are based primarily on the Army performance

specifications which, for the most part, represent performance levels

attainable by modern state-of-the-art commercial audio distortion analyzers.

The main objective in developing the test procedures has been to provide

measurement techniques which are accurate, repeatable, and simple to perform.

Above all, the procedures must be technically sound so as to provide an unbiased and objective evaluation of competitive instruments.

From a cursory inspection, of some of the procedures presented in this

report may appear to the reader to be overdesigned in terms of the suggested

test equipment. This may seem particularly apparent when only one procedure

1
is examined out of context with the entire set of procedures for the

distortion analyzers and the entire TMDE bid sample testing program. The reason for specifying instruments which in some cases appear as "overkill" are twofold: first, where possible, most of the tests are designed to provide

accurate results without having to resort to special fixtures and techniques,

rigorous accounting of errors, or highly skilled test engineers. Second,

since the TMDE Modernization Program is relatively new, part of the program

objective is to build a laboratory at CECOM with an inventory of modern

general purpose test equipment that will serve a wide range of bid sample

testing needs. Thus, most of the specific test equipment specified by make

and model represent equipment that is a part of, or will become, a part of the

CECOM laboratory.

This report is divided into three sections: background, audio distortion

analyzer applications and principles, and distortion analyzer performance

measurements. The first section gives a brief overview of the Army's TMDE

Modernization Program. The second section contains general information on the

applications and principles of modern audio distortion analyzers. The third

section discusses, in depth, the primary performance measurements with

emphasis on a preferred method, some alternate methods, and a discussion of error sources. The information in this last section is intended to provide

the theory and analysis to support the actual detailed procedures given in

Appendix B. The detailed procedures in this appendix are step-by-step

procedures intended to be used by the Army for evaluating bid samples to assure conformance to the set of Army specifications given in Appendix A. Also, included in,Appendix C are samples of appropriate data sheets and tables

for recording interim and final results. A program for generating an arbitrary waveform is provided in Appendix D. Appendix E shows the design and

characteristics of a low-pass filter that is used in some of the procedures,

and Appendix F lists all the test equipment and accessories required for the

test procedures.

Although the test procedures described in this report were specifically

designed for use by the TMDE Modernization Program, many of the tests can be

considered generic in nature and perhaps could serve as the basis of some type

of industry test standard for audio distortion analyzers.

2. BACKGROUND

The Department of the Army has undertaken a Test Measurement and

Diagnostic Equipment (TMDE) Modernization Program. The general goal of this

program is to provide TMDE for the Army, eliminate the prol iteration of

numerous types and models of such equipment, and thus reduce the logistical

burden. Specifically, the intent of the TMDE Modernization Program is to:

1. Introduce a minimum ensemble of different types and models of up-todate TMDE into the Army inventory,

2. Replace multiple generic types of TMDE with a single new item where

feasible and.

Continually assess the Army TMDE inventory to identify individual or families of TMDE that require replacement.

2

3 .
The acquisition of new TMDE items progresses through a two step

invitation for bid procedure. The first step begins with letter requests that

are released to potential offerors for bid samples. The offeror has a period

of 60 days to analyze the solicitation requirement and send bid sample

equipment to the Communications-Electronic Command (CECOM), Ft. Ntonmouth, NO

for testing. Equipment is evaluated for performance, useability,

maintainability, workmanship, ease of calibration, military suitability,

safety, and environmental capability. After the bid sample testing, only the

offerors with test equipment that meets the solicitation requirements are invited to submit bids. The second step occurs when the bids are received,

evaluated, and the lowest responsive bidder is awarded the contract. This

procedure is believed by the Army to provide reliable and maintainable test

equipment with superior performance characteristics for support of weapons

systems.

Bid sample equipment evaluation requires an established set of test

procedures which can objectively determine conformance to specifications.

Unlike some evaluations such as safety and workmanship which are more general

and widely applicable, electrical performance test procedures are by necessity

specification specific. That is, each particular electrical performance

specification must have a procedure. Although some equipment manufacturers

provide performance check procedures for purposes of incoming inspection, or readjustment to specifications, there is a lack of generic test methods

applicable to various classes of equipment that can be directly and

objectively used by the Army.

Therefore, before bid sample testing can proceed, appropriate test

procedures must be developed and validated. This report describes the test

procedures specifically developed by NBS for the Army to perform bid sample

testing of audio distortion analyzers.

3. AUDIO DISTORTION ANALYZER APPLICATIONS ^ PRINCIPLES

Modern audio distortion analyzers are fully automatic, programmable, and can measure Total Harmonic Distortion (THD) levels down to the order of 0.003%

(-90 dB). Also, these analyzers are designed to make Signal, Noise, and

Distortion (SINAD) measurements in addition to being versatile enough to be

used as a high sensitivity autoranging voltmeter, frequency counter, or even

as a low-noise amplifier. Distortion and SINAD measurements have, in the

past, required a great deal of operator control and interaction but

microprocessor control for the automatic tuning and amplitude leveling has

removed this burden from the classic audio distortion analyzer.

The term "audio" generally means frequencies within the range of human

hearing, (about 20 Hz to 20 kHz) although frequencies on either side of this

range are often loosely termed as "audio." Most audio distortion analyzers

have a range of operation that typically covers a frequency range from 20 Hz

to 100 kHz. Because of their wide bandwidth, most analyzers include filters

which allow bandwidth limiting, hum rejection, and weighted measurements of

noi se.
The primary application areas for distortion analyzers are general audio

testing and transceiver testing. In audio testing, a distortion analyzer can

be used to measure the frequency response and distortion characteristics of

filters, amplifiers, and high-fidelity audio systems. The most common measurements for transceiver testing are SINAD for FM receivers and

Signal-to-Noise (S/N) ratio for AM receivers. The above mentioned types of

testing all require a low-distortion, low noise signal source. Consequently,

some distortion analyzers also contain a built-in low-distortion source,

making the unit a complete, self-contained audio measurement system.

Distortion of electrical signals takes many forms. The basic causes of

distortion are nonlinearity in amplitude response and nonuniformity of phase

response. Distortion may be grouped into the following commonly encountered

types: [1]

1. Harmonic distortion is due to nonlinearities in the amplitude

transfer characteri sties. It causes a dispersion of energy that is

distributed in integer multiples of the fundamental frequency.

2. Intermodulation distortion is also due to nonlinearities in

amplitude transfer characteristics and causes a spurious output

resulting from the mixing of two or more signals at different

frequencies. The spurious output occurs at the sum or difference in

integer multiples of the original frequencies.

3. Phase distortion is a deviation from a constant slope of the output

phase versus. frequency response of a device. This deviation

produces echo responses in the output that precede and/or follow the

main response.

There are other specific types of distortion which are classified

according to their causes such as cross-over distortion or transient

distortion. These distortions, as well as other types, manifest themselves

in one or all of the above listed distortion types. Most audio distortion

analyzers are designed mainly to measure THD and SINAD. Intermodulation

distortion measurements can also be made with some audio analyzers provided

they contain the appropriate filters to give a weighted response that

conforms to a particular industry standard. However, most audio distortion

analyzers do not provide an intermodulation measurement capability.

THD is defined as the ratio of the total rms voltage in all significant

harmonics to the rms voltage of the fundamental. The ratio is usually

expressed as a percentage or in decibel units. A spectrum analyzer can be

used to make a THD measurement of a signal by measuring the magnitude of all

the harmonics and the fundamental. Then the ratio of the rms sum of all the

harmonics to the rms level of the fundamental is computed to obtain the THD.

The spectrum analyzer method, however, requires a costly instrument and is

tedious to perform. On the other hand, a distortion analyzer can quickly

make an accurate distortion measurement by removing the fundamental of the

signal being investigated and measuring the remainder relative to the signal.

Figure 1 shows the basic block diagram of a harmonic distortion analyzer

measurement. A distortion measurement made this way also includes effects

from noise and hum. Thus, the term (THD + N) has been recommended by the

Institute of High Fidelity [2] to distinguish distortion measurements made

4
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with a distortion analyzer from those made with a spectrum analyzer. An audio

distortion analyzer, therefore, measures distortion D according to the

following relationship:

1^ _ noise + distortion

~ fundamental + noise + distortion *

The distortion is usually converted and displayed as

Percent units = D x 100,

or dB units = 20 log D.

( 1 )

( 2 )

( 3 )

When using a distortion analyzer which makes a distortion measurement

according to the above expression, it is important to know that the

measurement is not exactly "total harmonic distortion" as defined when using

the spectrum analyzer method. The difference comes about for two reasons.

First, since the distortion analyzer measures, exclusive of the fundamental,

all harmonic signals, noise, and extraneous non-harmonic signals, the

indicated level of distortion may be considerably higher than that contributed

only by the harmonics. In order to separate certain extraneous signals such

as power line hum or out-of-band noise, selectable filters are usually

available to reject such extraneous signals. The second difference, although

small for low distortion, results because the distortion analyzer references

the total distortion (numerator) to the input signal (fundamental + distortion) - the denominator - as opposed to referencing the total distortion

to only the magnitude of the fundamental. In other words, a distorted signal

level is not quite the same as the level of the signal fundamental. An

example will perhaps best illustrate this point. Suppose that a given signal

has a one volt ac (rms)fundamental level and a 0.2 volt ac (rms) sum of all

harmonics. The THD of this signal would simply be 20 percent or one fifth the

fundamental. The same signal measured with a distortion analyzer will

indicate a slightly lower value because the distortion analyzer references the

harmonic level [0.2 volts ac (rms)] to the rms level of the "signal" (i.e.,

fundamental + harmonics) which in this example would be

(1)^ + (0.2)^ 1.02 V ac (rms). (4)

Thus, the indicated distortion becomes

0.2 V (rms)

1V02 V (rms)"

0.196 or 19.6%. (5)

The difference here amounts to only 2 percent below the actual THD, but it is

clear that the difference becomes significant at very high levels of

distortion.

6
Most distortion analyzers are equiped to measured SINAD. The SINAD

measurement is essentially the reciprocal of the distortion measurement.

Thus, a SINAD measurement is made according to the following relationship:

CTMAH fundamental + noise + distortion

noise + distortion ( 6 )

The SINAD is usually converted and displayed as

dB units = 20 log (SINAD). (7)

SINAD is a widely accepted method of specifying receiver sensitivity.

Receiver sensitivity is defined as the RF level that, when modulated with a pure audio tone, produces a certain SINAD at the receiver's audio output. The

"usable sensitivity" is generally defined as 12-dB SINAD which serves as a reference level where a tone can just be discerned in the noise [3]. Usually

the SINAD measurement is more heavily filtered than the distortion measurement

in order to smooth the noisy signals encountered in receiver testing.

Sometimes a psophometric filter is required in the receiver sensitivity

measurement. The psophmetric filter weights the frequency response of the

distortion analyzer with a bandpass characteristic that approximates the

response of human hearing. If a distortion analyzer employs such a filter

it is characteristics are specified by the C.C.I.T.T [4].

Figure 2 shows a block diagram of the essential elements contained in a modern automatic distortion analyzer. The particular architecture shown may

not necessarily conform to an actual instrument but rather is intended to

illustrate the basic principles involved. Specific details of control,

whether done directly in hardware or through the central processing unit,

(CPU) are not within the scope of this discussion.

The input stage is designed to accept the test signal in differential

form and convert it to a single-ended signal (referred to ground). The

differential input configuration helps to reject common-mode signals. The

input stage also contains appropriate attenuation networks for high level

signals and overload protection circuitry to protect the input circuits. The

signal is further amplified by a programmable gain amplifier which is set to

keep the signal level at the input detector within a narrow range to optimize

the detection accuracy. The input detector converts the rms level of the

signal to a. dc voltage. The dc output level of the input detector is used to

set the gain of the first programmable amplifier and becomes the denominator

of the distortion measurement or the numerator of the SINAD measurement. A

high-pass or psophometric filter can be inserted in the signal path between

the programmable amplifier and the notch filter. A 400 Hz high-pass filter is

often used to suppress power line hum or squelch tones used in some mobile

receivers. As mentioned previously, a psophometric filter can be switched in

at this point for certain receiver measurements.

In the distortion or SINAD measurement, the fundamental of the signal is

removed by a notch filter which is automatically tunec to the fundamental of

the signal. Auto-tuning of the notch filter is accomplished by several

methods which involve the CPU to control the internal analog tuning circuitry.

7
Input

Prog.

Gain

HP

Prog.

Notch

Prog.

Gain

LP

Buffer

Stage

Amp.

Filter

Filter

Amp.

Filter

Amp. 1I c

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Block

diagram

of

the

essential

elements

contained

ina

modern

audio

distortion

analyzer.
Large amounts of noise may prevent the automatic tuning circuits from

locking onto the fundamental during SINAD measurements. Thus, most distortion

analyzers require some manual tuning to bring the locking frequency within

approximately 5 percent of the source frequency in order for the system to

lock onto the fundamental.

A programmable gain amplifier following the notch filter is used to

amplify the low-level noise and distortion signals. The signal levels are adjusted to within a narrow range by the programmable gain amplifier to

optimize the output detector accuracy. If desired, a series of low-pass

filters can be switched in to remove high-frequency noise components in low

frequency distortion measurements. The two filters most commonly used are 30

kHz and 80 kHz low-pass filters with at least a 60 dB per decade rolloff.

The output detector converts the rms level of the signal to a dc voltage

which becomes the numerator in the distortion measurement and the demoninator

in the SINAD measurement. Rms detection is the most often used detection

method because it is proportional to the power of a signal. However, some distortion analyzers employ the option of "average" detection which was more popular in early designs.

The output from the second programmable amplifier drives a buffer

amplifier which provides an output signal that can be used to monitor the

processed signals with another instrument such as an oscilloscope.

If the distortion analyzer is to be used as a voltmeter, the notch filter

is switched out and the output level from the output detector is displayed.

Appropriate scaling is managed by the CPU's control of the programmable

amplifiers. Also, some distortion analyzers provide a display'*of the

frequency of the fundamental signal. Thus, the versatility of the instrument

is extended since it may be used as a general purpose frequency counter.

The audio distortion analyzer outlined in figure 2 is a very versatile

instrument. Its measurement flexibility comes from the CPU's ability to

process and display various measurements, and the measurement can be

completely controlled through the General Purpose Interface Bus (GPIB).

4. DISTORTION ANALYZER PERFORMANCE MEASUREMENTS

This section discusses the philosophy of the measurements employed in the

test procedures provided in Appendix B. The information in this section is

intended to provide an understanding of the measurements and some of the

details which must be considered. It is important that there be an understanding of the basic metrology required to perform the measurements

because no matter how detailed a particular procedure is prescribed and

followed, there are invariably situations that may require slight deviations

or modifications to a procedure. The format of this section is divided into

9
four groups of measurements: Input/Output Characteristics, Voltmeter ftode.

Distortion Mode, and Filter Characteristics. Under each of these groups,

particular measurements are discussed, with emphasis on a preferred method,

some alternate methods if applicable, and a discussion of error sources.

4.1 Input/Output Characteristics

The characteristics of the audio distortion analyzer signal input port

which are generally specified are: the input impedance, the common-mode

rejection ratio (for differential inputs), maximum input voltage, and input

over-voltage protection. A monitor output port is usually provided to permit

external instrumentation to monitor the processed signal. The output

impedance of the monitor output is usually specified. Other input-output

specifications such as physical configuration and location of connections do

not require a measurement.

4.1.1 Input Impedance

The input impedance specification relates to the loading that an instrument presents to a circuit or device under test. Input impedance is

often stated in terms of a dc resistance and a shunt capacitance. The user is

interested in this parameter to determine the effect that the instrument may

have upon the circuit under test. Since capacitive reactance varies with

frequency, in order for the input impedance specification to have the most

practical meaning, it is usually expressed in terms of a resistance and

a parallel capacitance rather than an impedance at a given frequency. In some applications, a low input impedance could upset the operation of the circuit

which is being measured. Most often, though, it is the finite input impedance

which interacts with an equivalent source resistance to cause a measurement

loading error.

For example, the input impedance of typical audio distortion analyzers

may be specified to be 100 kohms, accurate to ±2 percent, shunted by less than

300 picofarads. The effect of this input resistance and capacitance on the

accuracy of voltage measurements may be calculated by considering the circuit

shown in figure 3.

10
11

Equivalent

circuit

for

determining

input

impedance.
In this circuit, Rs is the equivalent circuit or device source resistance in series with the source voltage V5 being measured, Ri is the

instrument input resistance, and Ci is the instrument input shunt capacitance.

The fractional loading error, E may be expressed as

E . 1 . (V /V ) = 1 ! ^ , ’ ^ [(Ri + + (2>tfR5R^C.)2]i/2

(8)

where f is the frequency^

From this equation, and the values given above for Ri and Ci , it is

possible to determine the amount of error introduced by the loading effects of

the input impedance of the distortion analyzer when used in the voltmeter

mode. For example, if the user wishes to measure a voltage to within two

percent, even at low frequencies (less than 100 Hz) where the effects of the

shunt capacitance (second term of equation 8) may be considered negligible,

then the impedance of the voltage source must not exceed approximately 2000

ohms. On the other hand, for the same 2000 ohm source resistance, the total

loading error increases to almost four percent at 50 kHz due, in part, to the

300 pF input capacitance.

Measurement Technique

% Two methods can be used to measure the input impedance of the audio

distortion analyzer. The first method uses a direct-reading LCR meter to

measure the resistive and capacitive components of the input impedance. The

second method uses an external resistor in series with the input to obtain a voltage division between the resistor and the input such that the input

resistance and capacitance may be calculated.

The preferred method is to use a commercial digital LCR meter to directly

measure the input resistance and capacitance. Such instruments may be broadly

categorized, according to the technique used, into the bridge, voltage/

current, and Q methods. In the bridge technique, circuit conditioning required

to achieve a balance or null condition is processed to indicate the measured

values of the resistance and shunt capacitance. The voltage/current method

essentially uses Ohm's law in that a constant voltage or current is applied to

the unknown and the converse current or voltage is indicative of the unknown

impedance. The Q method utilizes the unique characteri sties of a resonant

circuit to determine Q, and indirectly L, C, and R.

When the LCR method is used, the measurement port of a voltage/current

type LCR meter is placed directly across the input port of the distortion

analyzer under test which should be energized. The input resistance and

capacitance may be read directly in terms of ohms and picofarads. Two

precautions are necessary to assure that proper measurements are made. First,

it is necessary that either the instrument under test or the LCR meter be

isolated from power- line ground.

12
The circuit configuration of the LCR meter is such that if the "low"

measuring terminal is grounded to the chassis, the LCR meter will not measure

correctly. Functionally, the LCR meter's "low" terminal is at virtual ground

but cannot be directly shorted to ground. When the measuring terminals of the

LCR meter are connected to the input terminals of the distortion analyzer, the

LCR "low" terminal will be grounded through the distortion analyzers 60 Hz

power-safety ground circuit.

The suggested method of breaking the ground circuit is to "float" the

chassis of the distortion analyzer which is powered through an isolation

transformer. "Floating" (disabling the power safety ground circuit) without

an isolation transformer is not recommended for safety reasons. It is not

necessary to use the isolation transformer when measuring the input impedance

of a differential input, since neither input is grounded. If the LCR "low"

terminal is grounded, a resistance and capacitance value will be displayed

which is far above or below the expected value.

The second precaution in using the LCR meter is to assure that the

distortion analyzer does not change ranges in response to the applied voltage

from the LCR meter. Range changes can cause the apparent input impedance of

the analyzer to change momentarily, forcing a range change in the LCR meter.

This in turn causes the voltage output of the LCR meter to also change. Such

range changing is manifested by a system oscillation wherein neither the LCR

meter nor the distortion analyzer obtains the proper range. The presence of

oscillating range changes is obvious by the unstable display of the LCR meter.

A second method that can be used to determine the input impedance is by

measuring the loading error expressed in equation 8 with a given source resistance. The method involves two steps. The first step is to obtain the

value of the input resistance, and the second step is to obtain the

capacitance. Determing input resistance consists of applying an ac voltage

from an oscillator through an external adjustable source resistance to the

input of the distortion analyzer which is set to the voltmeter mode. The

frequency of the oscillator is set to 100 Hz, and the amplitude is set to

approximately 2.0 V ac (rms). The external source resistance is set to zero

and the voltage displayed on the voltmeter is read and recorded. The external

resistance is then increased to a value such that the display is exactly

one-half the recorded value. At this point, the measured external source

resistance is equal to the input resistance. Note that the source resistance

of the oscillator must also be accounted for as part of the total source resistance. To obtain the input capacitance, the frequency of the oscillator

is increased to a frequency, f, of approximately 100 kHz. The external source resistance is set to zero, and the analyzer input voltage is read and noted as Vi. Then an external source resistance equal to the input resistance

previously determined is inserted between the oscillator output and analyzer

input and the voltage recorded as V 2 . The input capacitance, Cin,

may be calculated as

( 9 )

where Ri is the value of the input resistance determined in step 1.

13
Sources of Measurement Error

The errors associated with using the direct-reading LCR meter are attributable to uncertainties associated with the calibration accuracy of the

LCR meter and the uncertainties of the cable capacitance connecting the LCR

meter to the audio distortion analyzer under test. The basic calibration

accuracy of the LCR meter used in the procedure described in Appendix B is

specified by the manufacturer to be 0.2 percent of reading plus one digit for

capacitance measurements and 0.2 percent of reading plus two digits for

resistance measurements. The total worst case rms errors associated with the

LCR meter, considering the ranges used and the number of digits displayed, are

± 1.6 pF and 50 ohms for the measurement of parallel capacitance and

resistance, respectively.

The sources of error in using the second method are numerous, requiring

an independent measurement of external source resistance which must include

the source resistance of the test oscillator. The method also depends on the

linearity of the voltage measurement of the analyzer. Also, for low input

capacitances, the accuracy drops off rapidly as the measurement of the V 1 /V 2 ratio of equation (9) approaches a value of two. Because of the many sources

of possible error with this technique, the direct-reading LCR meter technique

is preferred.

4.1.2 Input Common-Mode Rejection Ratio (CMRR)

The input configuration of some audio distortion analyzers provides two

input ports for differential voltage measurements and rejection of common-mode

signals. In many applications, especially where the signal source is located

an appreciable distance from the analyzer, undesired ground loop signals can arise, particularly from the ac power source. These undesired signals appear

simultaneously on both input terminals; hence, they are referred to as common-mode signals. The common-mode gain is a measure of the amplification

of such a signal and should be as small as possible. The common-mode

rejection ratio (CMRR) is the ratio of the desired differential gain to the

undesired common-mode gain and should be as large as possible. CMRR is often

expressed in dB as 20 times the logarithm of the direct ratio.

Measurement Technique

A test method is described that will measure the CMRR of the differential

input over given ranges of differential gain, common-mode amplitudes, and

frequencies. The method is especially designed for instruments that have an autoranging capability that cannot be manually overridden. The measurement is

made with a center-tapped (CT) audio-frequency transformer which permits

coupling a common-mode signal with a balanced source impedance to both inputs

14
Coupling X

former

15

Fig.

4

Test

setup

for

measuring

the

common-mode

rejection

ratio

of

an

audio

distortion

analyzer

(preferred

method)
while simultaneously applying a given normal-mode signal. The test setup is

shown in figure 4. Applying a normal-mode signal simultaneously with a common-mode signal forces the instrument's autoranging system to settle at one particular range independent of the common-mode level. A spectrum analyzer is

used to measure the respective normal and common-mode signals appearing at the

monitor output terminals of the distortion analyzer. The equipment required

for this test and its essential characteristics are:

1.

Audio Oscillators - Frequency and amplitude coverage over range of interest.

2. Spectrum Analyzer - Frequency coverage over range of

interest. Sufficient dynamic range

to measure the common-mode input

and output level. A dynamic range of

at least 10 dB greater than the measured

CMRR.

3. Coupling Transformer - Line to line type, 1:1 overall turns

ratio, primary 600 ohms, secondary

600 ohms CT, frequency response 100 Hz

to 10 kHz, ± 3 dB.

The controls of the distortion analyzer are set to operate in the

voltmeter mode with all filters turned off. The frequency of the oscillator

which supplies the normal -mode signal is set near the mid-band frequency of

the distortion analyzer which is usually in the range of 1 to 5 kHz. The

amplitude of the normal -mode oscillator is set to the desired normal -mode

level at which a CMRR is to be made. Different normal-mode levels will cause

the programmable amplifiers within the distortion analyzer to shift ranges

which may change the normal-mode differential gain which in turn affects the

CMRR. The actual normal-mode level must be measured and recorded. It is

suggested that the spectrum analyzer be used to measure all levels even though

the distortion analyzer itself can be used to measure the input normal -mode

level. The frequency of the audio oscillator which supplies the common-mode

signal is set to the frequency of interest (usually the power line frequency

or harmonics of the line frequency). The level of the common-mode signal is

set to the desired level which must be within the maximum common-mode

amplitude specification of the distortion analyzer. An ac calibrator can be

used in place of an oscillator for the common-mode signal to obviate the need

to separately measure the input common-mode amplitude. The spectrum analyzer

is then used to measure the amplitudes of the normal and common-mode signals

at the distortion analyzer monitor output. The CMRR is calculated as

CMRR = 20 log

(V ) (V. )

^ onm^ ' icm'^

W-'' TT? ) inm'^ ^ ocm^

( 10 )

16
where Von^i is the measured output normal -mode amplitude,

Vinm is the measured input normal-mode amplitude,

Vocm is the measured output common-mode amplitude, and

Vicm is the measured input common-mode amplitude.

An alternate and somewhat simpler method for determining the CMRR is

described. It is the method most often suggested by manufacturers in their

description of performance tests. The alternate method, however, must be a approached with some caution, especially if the distortion analyzer has an autoranging capability. It is recommended that all autoranging systems be

overridden and measurements made at fixed gain settings. Some distortion

analyzers have both a preamplifier and post-notch filter autoranging

capability. The manual control of ranges may have to be set via the GPIB in some distortion analyzers.

The test setup for the alternate method of measuring the CMRR is shown in

figure 5. The common-mode voltage source is connected between the common

ground of the audio distortion analyzer and the two input terminals (high and

low, + or -) which are jumpered together. A digital multimeter measures ac voltage from the common-mode input source at the monitor output terminal. The

ratio of the monitor output voltage to the input common-mode amplitude

establishes the common-mode gain. The normal -mode internal gain from the

input to the monitor output can either be measured directly or the gain factor

can be determined from the manuf acturer ' s specification. If the normal-mode

gain is to be measured, then all autoranging functions must be overridden and

manually set. The errors associated with this measurement are the same as in

the preferred method.

Sources of Measurement Error

The principle source of error arises from the uncertainties of the

amplitude of input and output normal and common-mode amplitudes with the

spectrum analyzer. A ±10 percent error in the measurement of the normal -mode

gain and the common-mode gain can produce a maximum error of ±1.74 dB in the

CMRR. Likewise, a ±1 percent error in the two gain measurements will produce

a ±0.174 dB error. The character! sties of the coupling transformer contribute

negligible error to the CMRR measurement since it serves primarily as a means

of providing a balanced normal-mode signal for the differential input to the

distortion analyzer. If the secondary center-tap is unbalanced, this will cause an unbalance in the reflected source impedance of the normal -moae

generator. This in turn unbalances the effective source impedance of the

common-mode generator as seen by the differential inputs of the distortion

analyzer. The common-mode imput impedance of most differential amplifiers is

high but not infinite, and thus, an unequal source impedance will produce an unequal attenuation at each input which is amplified by the differential

amplifier. The result is a lower measured CMRR than that which is inherent in

the amplifier itself. Some specifications specify a given source impedance

unbalance which is a much more difficult CMRR specification to meet, since in

order to maintain a high CMRR under this condition, requires very high

common-mode impedances. By connecting the common-mode signal generator to tne

17
18

An

alternate

method

of

measuring

the

commont-mode

rejection

ratio

of

an

audio

distortion

analyzer.
transformer secondary center-tap, the CMRR measurement is made with a balanced

source impedance. An imbalance of ±10 percent of the secondary center-tap

will cause a negligible change in the CMRR measurement, considering a nominal

normal and common-mode source resistance of 600 ohms, a typical common-mode

input impedance of 100 kohms, and a 40 dB CMRR specification. The effect of a common-mode source impedance imbalance can be greatly diminished by making the source impedance of the normal -mode generator very small.

4.1.3 Input Protection

The audio distortion analyzer should be protected from excessive voltages

applied at the input terminals. This protection is important from the

standpoint of reliability and safety. Overvoltage protection is usually

specified to be automatic in the sense that the user does not need to perform

a manual reset or replace fuses in the event of an application of excessive

voltage. The input circuitry must be able to respond rapidly to large

overvoltage signals (within specification) without degrading the performance

and without causing a safety hazard to the user.

Measurement Technique

Testing for input protection is a fairly simple and straightforward

procedure. The test requires a source of voltage equal to the specified

overvoltage specification limit. Specifying an overvoltage in rms volts

without specifying the type of wavefjDrm can be ambiguous since such a specification fails to define the peak amplitude. Generally, the automatic

protection circuitry is designed to respond to the peak amplitude; the rms

level may be useful for determining the maximum power dissipated in the input

circuitry without degradation. The input protection test procedure should be

done prior to all other performance tests as a means of ensuring that a given

overvoltage has not degraded the overall performance. The procedure is to

apply the specified overvoltage to the input terminals of the distortion

analyzer for a period of at least two minutes while observing for any obvious

signs of component overstress such as smoke or sparks. If there are no obvious faults, then the overvoltage is removed and all other test procedures

are performed.

4.1.4 Monitor Output Impedance

The output impedance specification is a measure of the internal

resistance of the audio distortion analyzer as presented at the output monitor

connector. This output is provided to permit external instrumentation, such

as voltmeters and oscilloscopes, to measure the signals after they are processed by the circuitry of the distortion analyzer. The output signal

present at the output connector depends on the mode in which the distortion

analyzer is used. For example, if the analyzer is in the distortion mode, the

signal present at the output connector provides a scaled presentation of the

19
o

O CO CO o o ®

<0 -J QC

c

E

sO)

4-> O) -O

S-o

1/1 -M • •I- o»

=J u

u c

i- ra

•t- ^_) O 1/1

-»-> 1/1 C OJ

Ol ^

-u > 3

•1- CL 3 +J O' O

LxJ O

U3

Ol

20
input signal with the fundamental frequency removed. For example, the user may wish to connect a frequency spectrum analyzer to this port to determine

the relative amplitudes of the harmonics contained in the input signal.

It is desirable for the output impedance to be as low as possible. This

permits external instrumentation to be connected to the distortion analyzer

with a minimum of "loading" or reduction in signal amplitude at the output

connecter when an external impedance is attached.

Measurement Technique

The measurement of the output impedance is done in two steps. The first

step consists of setting the controls of the distortion analyzer such that the

filters are removed and that the signal at the output of the distortion

analyzer is a scaled presentation of the input signal. A 1 kHz signal from an audio oscillator is then applied to the input of the distortion analyzer and

the voltage at the output connector is measured with a high input impedance

(nominally 1 megohm) ac digital voltmeter. The ^plitude of the voltage from

the audio oscillator is adjusted to obtain a reading on the digital voltmeter

of approximately 1 V ac (rms). The exact value of the open circuit, or "unloaded," voltage at the output connector is recorded as Vi.

The second step consists of placing a resistance equal to the expected output

resistance across the output connector of the distortion analyzer and

remeasuring the amplitude of the voltage at the output connector. The

resultant voltage is recorded as V 2 . Figure 6 shows the equivalent circuit

from which an expected internal output resistance, Rout> 0^ 600 ohms can be

calculated from Vi, V 2 , and a 600 ohm load resistor. The output resistance is

calculated by the equation

Rout

=

Sources of Measurement Error

The measurements errors for this procedure arise from two sources.

First, the 600-ohm load resistor may deviate slightly from its prescribed

tolerance value. Second, the internal impedance of the voltmeter loads the

circuit slightly and results in lower voltages being recorded than are actually present without the voltmeter being connected.

Choosing a load resistance approximately equal to the value of the

expected output resistance represents the best compromise in making an accurate measurement of output impedance. Under such conditions, the

tolerance of the output resistance is equal to the tolerance of the load

resistance and the voltage ratio V 1 /V 2 is easily measured with a digital

voltmeter.

The effects of voltmeter loading in the measurement of output resistance

in the 600 ohm range can be neglected since most digital voltmeters have at

least a one megohm input impedance. Usually the monitor output impedance

21
specification of the distortion analyzer places a loose tolerance on the

actual value for purposes of specifying a nominal value. Highly accurate

determinations of output impedance for a monitor output port are generally not

necessary since it is used primarily for monitoring and does not affect the

basic accuracy of distortion measurements.

4.1.5 Monitor Output Frequency Response

The monitor output signal connector on the audio distortion analyzer

provides a convenient way of examining the effects on the signal processed by

the input scaling circuitry and the notch filter. In the voltmeter mode, the

monitor output signal is a scaled version of the input signal with a scale

factor inversely proportional to the range setting. In the distortion mode,

this signal is obtained after the notch filter such that, in addition to

scaling, the fundamental frequency has been filtered out of the signal. Many

of the distortion analyzers amplify the signal after the notch filter.

Thus, the scale factor may not be the same in the distortion mode as in the

voltmeter mode.

It may be difficult to determine the scale factor for those distortion

analyzers that do not have provision for manual setting of the input

sensitivity range. For those instruments that provide only automatic ranging

capability, the frequency response may be checked using a fixed input voltage

at various selected frequencies such that the audio distortion analyzer do^s

not change range.

Measurement Technique

The frequency response of the signal provided by the monitor output is

checked by applying an accurately known ac signal at several frequencies to

the input, and measuring the monitor output signal with an ac voltmeter. For

analyzers which can be manually ranged, a range should be chosen such that the

signal at the monitor output is maximum without overloading. For instruments

which can only autorange, care must be taken to watch for range changes during

the test. If range changes occur, then the test must be rerun at a slightly

higher or lower voltage such that no range changes take place. An amplifier

will need to be employed to boost the test signal levels above the maximum

output voltage of the test generator. The data taken at 1 kHz is used as the

reference value. The scale factor at the other frequencies must be within the

specific tolerance of this value.

Sources of Measurement Error

The main sources of error are the flatness of the frequency responses of

the ac calibrator, power amplifier, and the ac voltmeter. This can be checked

by directly connecting the calibrator to the ac voltmeter and making the same

set of measurements. The errors in this case should be about 10 times lower

than the tolerance for the test. If this is not the case, then the data must

be corrected using this calibration.

22
4.1.6 Monitor Output Linearity (Absence of Clipping)

The distortion analyzer must accurately measure the distortion of signals

containing waveform abberations such as spikes. If the input circuitry clips

these spikes then the distortion reading will be in error. Clipping can be

detected by comparing the input signal with the signal from the monitor output

connector using a dual channel oscilloscope with variable gain. The two

signals can be placed at the same location on the screen. Clipping will be

indicated by the presence of the signal overlap everywhere except at the

peaks.

Measurement Technique

The test signal used for this test is the same as that described in 4.3.2

(3:1 crest factor signals). Refer to that section for a detailed description

of the signal. For distortion analyzers whose ranges can be manually set,

each range should be checked by applying an input signal with an appropriate

crest factor and an rms amplitude equal to the full-scale voltage of that

range. For analyzers which can only autorange, this test can be performed at

selected voltages.

Sources of Measurement Error

The main error source is any nonlinear amplitude response of the

ocilloscope to the two signals, which may have significantly different

amplitudes. Most oscilloscopes will perform satisfactorily for this test

since only gross peak limiting is being checked.

4.2 VOLTMETER MODE

4.2.1 Voltmeter Accuracy and Range

Since all of the essential elements of an ac voltmeter are contained in an audio distortion analyzer, the versatility of the instrument is enhanced by

being able to use it as an ac voltmeter. Ideally, an ac voltmeter should have

a uniform response over a specified frequency range, should be capable of

making measurements to a predetermined accuracy, and should present stable

readings with changes in environmental factors such as time, temperature, and

line voltage.

Measurement Technique

The accuracy of the voltmeter contained in the distortion analyzer can be

verified by applying various ac voltages over a range of frequencies to the

voltmeter from a precision ac source. The voltages and frequencies chosen are commensurate with the range of the voltmeter contained in the distortion

analyzer under test. Such a test is easily accomplished by connecting the

distortion analyzer (set to the voltmeter mode) to an ac source or meter

23
calibrator with sufficient accuracy to assure that errors in the readings are due to voltmeter errors and not due to errors in the source itself. The

readings obtained on the voltmeter are then compared to the limits of accuracy

given in the specifications. Those readings which exceed the limits of

specified accuracy fail the test.

Sources of Measurement Error

The specified amplitude accuracy of most calibrators is a function of

both output voltage and frequency. The following table summarizes the

accuracy of one particular calibrator which is used in the procedure outlined

in Appendix B.

Table 1 Typical AC Calibration Accuracy Specifications

Frequency

Accuracy

1 to 100 mV

Range

Accuracy

1 to 100 V Range

10 Hz to 30 Hz ± (0.1% + 10 uV) ± (0.1% + 0.005 V)

30 Hz to 20 kHz ± (0.02% + 10 uV) ± (0.02% + 0.002 V)

20 kHz to 50 kHz ± (0.05% + 20 uV) ± (0.05% + 0.005 V)

50 kHz to 100 kHz ± (0.05% + 20 mV) ± (0.05% + 0.005 V)

The greatest uncertainties of the output voltage of the meter calibrator

occur when the calibrator is used to generate a 1 mV signal at the lowest

frequency (10 Hz). Since the specifications call for a few percent accuracy

over the entire range it is clear that the accuracies shown in Table 1 above

are sufficient to calibrate the distortion analyzer in the voltmeter mode.

4.2.2 Bandwidth

Significance

The bandwidth of most audio distortion analyzers spans a frequency from a few hertz to several hundred kilohertz. Strictly speaking, the bandwidth is

the difference between the upper and lower limiting frequencies, but often is

simply specified as a minimum upper limiting frequency. The commonly defined

limiting or cutoff frequency is the point where the response is three dB less

than a reference level (usually the mid-band level). Bandwidth measurements

24
should be made over the entire amplitude range or, at least, at the lower and

upper ranges. A measurement at the lowest amplitude range forces the system

to operate at maximum gain while a measurement at the upper range ensures that

the internal attenuators are not limiting the bandwidth.

Measurement Technique

Measurement of the bandwidth, or more specifically the upper cutoff

frequency limit, is a straightforward procedure requiring only a source which

has a flat frequency response from midband (one kHz) to the upper cutoff

frequency (300 kHz). The most convenient source for this frequency range is a precision ac calibrator and high voltage power amplifier system. An audio

oscillator can also be used but the flatness of the frequency response must be

verified. The measurement is made using the distortion analyzer in the

voltmeter mode to display the input voltage amplitude in dB. All filters must

be switched out of the signal path. The test source is connected to the

distortion analyzer input and the frequency of the calibrator is set to about

one kHz; then the level displayed is referenced to zero dB. The frequency is

changed to the specified minimum and maximum bandwidth frequencies and the

levels displayed at both frequencies are noted.

Sources of Measurement Error

The primary source of error in this measurement is the flatness of the

amplitude versus frequency of the source. If the source does not have a •specified amplitude/frequency accuracy, it must be determined by independent

means. High level measurements require special purpose precision amplifiers

whose bandwidth should exceed the minimum specified bandwidth by at least a factor of three in order to keep the measurement error within five percent.

4.3 DISTORTION MEASUREMENTS

As described in section 3., the distortion of a signal is defined as the

ratio of the rms amplitude of the harmonics, noise, and nonharmonic signals to

the rms amplitude of the total signal which includes the fundamental, its

harmonics, noise, and nonharmonic signals. The SINAD of a signal is the

reciprocal of this ratio. All the distortion performance tests described in

this report use the method of stimulating the distortion analyzer under test

with a signal whose distortion has been determined by independent means. Three types of signals are used to fully measure the range and accuracy of the

distortion analyzer in the distortion and SINAD mode. The first type of

signal stimulus contains a single harmonic, either the second or the third.

This signal is created by two independent sine wave sources that are added

together. This type of signal is used for the "two sine wave test." The

second type of signal stimulus is one that has a high crest factor and a broad

spectrum of harmonics. This signal consists of a distorted sine wave that has

a defined pulse at the crest of the wave. The high crest factor signal serves

two purposes; it tests the autoranging circuits' ability to pass such a signal

without clipping, and it also tests the ability of the inst'^ument to measure a

25
signal with a broad spectrum of harmonics. Testing with this type of signal

is called the "3:1 crest factor signal test." The third type of performance

measurement uses a sine wave at the fundamental frequency in the presence of

noise. The test with this type of signal is called the "SINAD test." For all

of the above types of signals, a range of amplitudes, fundamental frequencies,

and distortion levels are used to determine the accuracy of the audio

distortion analyzer. The following list gives the test instrumentation and

associated essential specifications required for making distortion

measurements good to an uncertainty of

± 0.1 dB:

1. Audio Oscillator - Frequency and amplitude coverage over the range of

interest. Output impedance 600 ohms or use series resistor.

Switched attenuator with range sufficient to drop output by more

than 40 dB without changing output impedance.

2. Low Distortion Oscillator - Frequency and amplitude coverage over range of

interest. Output impedance 600 ohms or use series resistor.

Switched attenuator with range sufficient to drop output more than

20 dB below the lowest distortion level being tested. Distortion of

output signal at least 10 dB less than lowest distortion level being

tested.

3. AC Voltmeter - Frequency and amplitude coverage over range of interest.

Uncertainty less than 0.5 percent.

4. Power Amplifier - Frequency and amplitude coverage over high voltage range

of interest. Distortion level of output at least 10 dB below lowest

distortion level to be tested.

5. Spectrum Analyzer - Must cover frequency range from 20 Hz to 300 kHz, and

amplitudes from 30 mV to 130 V ac (rms). (Note: an external

attenuator probe may be needed to cover the high voltages).

Absolute accuracy over these ranges must be ± 1 dB or better.

Stabi 1 ity must allow special calibrations of limited frequency

ranges to achieve an accuracy of better than ± 0.1 dB.

6. Noise Generator - Flat noise spectrum from 20 Hz to 100 kHz within ± 3 dB.

Attenuator switch settings over 40 dB. Stability over one hour of

better than 0.1 dB when measured with a broadband ac voltmeter.

4.3.1 Two Sine Wave Test

One very common form of distortion is harmonic distortion, where one or more harmonics of the fundamental are present with the fundamental. This type

of distortion is simulated in this test by combining two signals which are harmonically related (i.e., the fundamental and one harmonic). Combining the

two signals must be done in a manner which does not introduce any additional

unknown distortion into the two signals. Accurate knowledge of the amplitudes

of the two signals then determines the simulated distortion level.

26
o

o

27

Test

setup

for

measuring

distortion

accuracy

with

the

sine

wave

signals.

Note:

the

600 U

series

resistors

may

be

omitted

if

the

oscillators

have

an

output

impedance

of

600

0

or

greater.
Measurement Technique

For low voltages, one easy method of combining the signals is to use a resistive divider as shown in figure 7. If the two oscillators have a high

output impedance (600 ohms or greater), then the two oscillator outputs can be

directly connected in parallel. If they have low output impedances, then

nominally equal valued resistors must be placed in series with each output

before the two oscillators are connected together. This will result in output

voltages of about one half the open circuit voltages. The amplitude of each

oscillator is measured by an ac voltmeter with the other oscillator set to a very low level. For each measurement, the other oscillator must be set to at

least 20 dB below the amplitude of the oscillator being measured. In no case should either oscillator be disconnected or switched off during these

measurements, since the change in circuit loading will cause a large error in

the measured amplitude.

The use of 600 ohm external resistors to sum the two signals is

appropriate for amplitudes of 10 V ac (rms) and below. One watt resistors are recommended to minimize resistance changes due to a resistor temperature

coefficient. A resistance value of 600 ohms was chosen because a number of

oscillators are commercially available with this output impedance. For low

voltage levels, a 600 ohm resistance allows easy addition of signals without

drawing large amounts of power. Also, 600 ohms is low enough that the input

impedance of voltmeter, oscilloscopes, and distortion analyzers, which are typically one megohm, do not significantly disturb the circuit. For testing

distortion at higher voltages, a power amplifier is used to amplify the

combined two sine wave signal. However, the power anplifier must exhibit low

distortion. The distor.tion level of the power amplifier will limit ’the range

of distortions that can be applied to the distortion analyzer under test. The

distortion contributed by the power amplifier should be at least 10 dB below

the lowest distortion level that is to be measured.

Sources of Measurement Error

The main sources of error for this measurement are dependent on the

accuracy with which the amplitudes of the two sine waves can be measured, the

inherent distortion of the oscillators, and any distortion introduced by the

circuit used to combine the two signals. The voltmeter specified for the test

should have an accuracy of better then 0.5 percent which will result in an error of less than 0.05 dB in the measured distortion. The error caused by

the contribution of the one oscillator signal which is set to only 20 dB below

the level of the oscillator level being measured is about 0.5 percent. This

also translates to an error of less than 0.05 dB in the measured distortion.

The distortion caused by the resistive divider used to combine the

signals and by the high voltage amplifier used in the high voltage

measurements can be checked with a spectrum analyzer. The spectrum analyzer

should be used to look for harmonics and interharmonics, (sum and difference

of the two frequencies) for each oscillator signal when both are present. The

oscillator that provides the larger fundamental signal must be a

28
fO

CO

29

Test

setup

for

measuring

distortion

accuracy

with

signals

that

have

3

to 1

crest

factor.
low-distortion oscillator since its distortion limits the range of distortion

levels that this test can cover. The distortion of the other oscillator is

not as critical.

4.3.2 3:1 Crest Factor Signal Test

High crest factor signals are used to measure the tolerance of

instruments to clipping. Generally the autoranging circuits and overload

indication circuits respond to the rms value of an applied signal. When a full scale signal is applied to an instrument, for a given range, that

instrument should still not clip signals which have moderately high crest

factors. The crest factor of a waveform is the ratio of its crest (peak,

maximum) value to its root-mean-square (rms) value [5].

Measurement Technique

The 3:1 crest factor test waveform is generated using an arbitrary

waveform generator in the test setup shown in figure 8. The program for the

waveform is loaded into the waveform generator from a desk-top computer via

the IEEE 488 standard interface bus. A listing of the program is given in

Appendix 0. The waveform is a sine wave with a single cycle of a higher

harmonic

is given

superimposed on the peaks,

by

An analytic expression for this waveform

V(t) = sin(u)t) + P(t) (12)

where

/ A(1 + cos ( Hoot - -^) )

,

2

- H

< “t < 2 ^ H

p(t) = |-A(1 + cos(Hwt - -^^)), for ^ ^

< o)t < -^ + ^

(13)

( otherwi se

and where m is the angular frequency in radians per second, A is the amplitude

of the harmonic, and H is the harmonic number. Figures 9 and 10 are examples

of signals which have 3:1 crest factors. The signal represented in figure 9 uses a pulse of the 9th harmonic with an amplitude of 1.86 and the one in

figure 10 uses the 19th harmonic with an amplitude of 0.826. The frequency

spectra for these signals are shown in figures 11 and 12. The harmonics for

the 9th harmonic pulse start out higher than those for the 19th harmonic but

decrease more rapidly. The test procedure calls for measuring all the

harmonics greater than two percent of the fundamental or less than 34 dB below

the fundamental. Tables 2 and 3 give the harmonic amplitudes for the 9th and

19th harmonic pulses, respectively. Table 4 gives the crest factors that will

result from various combinations of amplitude and harmonic numbers. It can be

used as a guide in selecting the appropriate amplitude and harmonic

combination desired.

30
Table 2 Magnitude for the 9th Harmonic Pulse

1

COEF FREQUENCY kHz MAGNITUDE (dB)

1 1.953 - .92

3 5.859 -8.30

5 9.766 -9.44

7 13.672 -11.21

9 17.578 -13.69

11 21.484 -17.07

13 25.391 -21.66

15 29.297 -28.30

17 33.203 -40.65

19 37.109 -44.20

21 41.016 -39.18

23 44.922 -40.76

25 48.828 -46.87

27 52.734 -127.68

29 56.641 -51.06

31 60.547 -49.21

33 64.453 -52.05

35 68.359 -61.73

37 72.266 -63.24

39 76.172 -56 .60

31
Table 3 Magnitude for the 19th Harmonic Pulse

COEF FREQUENCY kHz MAGNITUDE (dB)

1 1.953 -4.63

3 5.859 -21.35

5 9.766 -21.60

7 13.672 -21.98

9 17.578 -22.49

11 21.484 -23.13

13 25.391 -23.92

15 29.297 -24.86

17 33.203 -25.96

19 37.109 -27.24

21 41.016 -28.71

23 44.922 -30.41

25 48.828 -32.37

27 52.734 -34.65

29 56.641 -37.33

31 60.547 -40.59

33 64.453 -44.71

35 68.359 -50.49

37 72.266 -61.54

39 76.172 -83.21

Table 4 Crest Factors Resulting From Various Combinations

of Amplitude and Harmonic Number

Harmonic

Number 0.75 1

/ 1.5

\mpl itude

2.0 2.5 3.0

9 2.48 2.66 2.89 3.03 3.13 3.19

11 2.60 2.82 3.11 3.29 3.40 3.48

13 2.69 2.95 3.29 3.50 3.64 3.74

15 2.77 3.05 3.44 3.69 3.86 3.98

17 2.84 3.14 3.58 3.86 4.05 4.19

19 2.89 3.22 3.70 4.01 4.23 4.38

21 2.94 3.29 3.80 4.15 4.39 4.56

32
Sources of Measurement Error

One source of error in measuring crest factor is neglecting to measure

all the harmonics present in the signal. Tables 2 and 3 show that for the 9th

harmonic pulse waveform, the amplitudes of 7 harmonics out to the 15th

harmonic must be measured, whereas for the 19th harmonic pulse, 13 harmonic

amplitudes are needed out to the 27th harmonic. The error associated with

ignoring the higher harmonics is 0.005 dB for the 9th harmonic pulse and 0.057

dB for the 19th harmonic pulse. The errors that result from a limited number

of harmonics are shown below in Table 5.

Table 5 Error Resulting From Using a Limited Number

of Harmonics to Calculate THD

Number of

Harmonics

Highest

Harmonic

9th Harmonic Pulse

Error (dB)

19th Harmonic Pulse

Error (dB)

1 3 6.8 15.1

2 5 2.8 9.5

4 9 0.42 4.5

6 13 0.27 2.15

‘7 15 0.005 1.46

8 17 0.004 0.96

10 21 0.002 0.37

12 25 0.000 0.11

13 27 0.057

14 29 0.026

15 31 0.012

16 33 0.006

18 37 0.005

Another error source is the inaccuracy of the harmonic amplitude

measurements. Spectrum analyzers typically specify the accuracy of a single

frequency measurement but usually do not specify the relative accuracy. The

important error parameter for distortion measurements is the accuracy with

which the harmonics are measured relative to the accuracy of the fundamental

measurement. As long as these ratios are measured accurately, the distortion

measurement is accurate. The spectrum analyzer should be checked for this

33
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37
relative accuracy at the frequencies and amplitudes at which distortion

measurements will be made. The procedure for doing this is given below.

Calibrating the Spectrum Analyzer

The spectrum analyzer is calibrated by applying accurate ac signals of

the same frequency and amplitude as the fundamental and harmonics of the 3:1

crest factor signal. These signals are applied and measured one at a time.

The known signals can be obtained either from an ac calibrator or from a signal generator and measured by an ac voltmeter. The spectrum analyzer is

set manually such that the range does not change between making the

fundamental measurement and the harmonic measurements.

The approximate amplitudes used for calibrating the spectrum analyzer can

be obtained from Table 2 or 3 or by making a spectral measurement of the high

crest factor signal that will be used. First set the ac calibrator to the

amplitude and frequency of the fundamental. Manually set the range of the

spectrum analyzer so this signal is near full scale. Set the sweep to a range

that will cover all harmonics, and as in the 3:1 test procedure, set the sweep

rate to two steps below the automatic setting. Set the vertical range to 5 dB/div. Then without changing the spectrum analyzer settings, record the

amplitude of the fundamental and, after resetting the ac calibrator frequency,

the amplitude of each harmonic.

To determine the relative accuracy of the spectrum analyzer, one must

compare the ratio of the measured harmonic amplitude to the measured

fundamental amplitude, with the expected ratio based on the ac calibrator

settings. The percentage of error** in the measured ratio is then calculated

for each harmonic. If the errors are less than two percent then no correction

will be necessary, since this error will cause less than 0.1 dB error in the

distortion reading. For larger errors, the readings should be corrected. If

the errors are biased in one direction, then it may be possible to correct

only the fundamental reading to get all the remaining errors less than two

percent. The correction to use for the fundamental is the weighted average of

the harmonic ratio errors. Each error should be weighted by the square of the

harmonic amplitude ratio. If the errors are not biased, then each harmonic

measurement must be corrected individually. Without much loss in accuracy the

corrections can be made to only the larger harmomics, say to those whose

amplitudes are greater than half the largest harmonic amplitude.

Some of the distortion measurements are made at amplitude levels which

exceed the input level of the spectrum analyzer. Under this condition the

test procedure specifies an attenuator probe. It is important that the probe

is properly compensated for a flat frequency response when connected to the

spectrum analyzer input. The probe can be checked by connecting the tip to

the spectrum analyzer's tracking generator while adjusting the probe for the

best flatness in frequency response particularly over the bandwidth of

interest

.

38
39

Fig.

13

Test

setup

for

measuring

SINAD

accuracy.

Note:

the

600 o

seiies

resistors

may

be

omitted

if

the

oscillator

and

noise

generator

each

have

an

output

of

600

il

or

greater.
The above test and calibration of the spectrum analyzer is repeated for

each fundamental amplitude and frequency that will be used to measure the

distortion of the 3:1 crest factor signal.

4.3.3 SINAD TEST

The SINAD of a signal is the reciprocal of its distortion. For

measurements in dB this means changing the sign of the value. Thus, -50 dB of

distortion becomes +50 dB of SINAD. Although both distortion and SINAD

measurements can determine the ratio of a fundamental to noise and harmonics,

traditionally SINAD is used where the predominant interfering signal is noise

rather than harmonics. Some distortion analyzers incorporate some special

features in the SINAD mode which enhance its ability to make measurements of

noisy signals. These features may include a narrower search range for the

fundamental frequency which requires an approximate frequency to be entered

into the distortion analyzer. Alternatively, a locking feature may be used

that maintains the notch filter at one frequency even though the amplitude of

the signal being measured is reduced close to the noise level.

Measurement Technique

The SINAD test is similar to the two sine wave test. The signal from a low distortion oscillator provides the fundamental signal and is combined with

the signal from a noise generator. A 600 resistor is placed in series with

each generator and then the generators are connected together in parallel. As

discussed in 4.3.1, if the generators already have a high output impedance,

the 600 n resistors are not used.

Figure 13 shows the test setup for the SINAD test. The setup is similar

to the two sine wave test setup but with the addition of a low-pass filter

between the generators and the distortion analyzer and the ac voltmeter. The

low pass filter is needed to match the bandwidth of the distortion analyzer to

that of the ac voltmeter. The filter limits the high frequency noise to below

the bandwidth limit of both instruments.

The amplitudes of both the oscillator and the noise generator are measured sequentially by the ac voltmeter with the other generator set to as near zero as possible. For each measurement, the one generator must be at

least 20 dB below the amplitude of the other generator that is being

measured. In no case during the test can one of the generators be

disconnected or turned off. This would change the circuit loading between the

two generators and cause a large error in the measured amplitude.

As with the two sine wave test, a power amplifier is necessary to provide

signals with an amplitude greater than 10 V ac (rms). This must be a low

distortion amplifier, since it will be amplifying the fundamental signal. The

distortion level of this amplifier places a lower limit on the range of

distortion that can be measured. A low-pass filter must be placed on the

output side of the amplifier to limit out-of-band noise contributed by the

amplifier. The filter must be designed to handle the power levels present at this location. Appendix E gives the details of an appropriate filter for this

application. 40
41

Test

setup

for

measuring

residual

distortion

and

noise.
Sources of Measurement Error

One potentially significant error source for SINAD measurements is the

failure of the low-pass filter to properly limit the high-frequency noise. In

general, the bandwidth of the ac voltmeter will be significantly greater than

that of the distortion analyzer. The cutoff frequency for the low pass filter

must be significantly below the bandwidth of the distortion analyzer. One

method of checking the adequacy of the filter is to compare the noise

amplitude measurements of the ac voltmeter to those of the distortion

analyzer. This is done by setting the distortion analyzer to the ac voltage

mode and the low distortion oscillator to its lowest level. Then, for a series of noise amplitudes, compare the readings of the distortion analyzer to

those of the ac voltmeter. The readings should be within ±3 percent of each

other. If this is not the case, a filter with a lower cutoff frequency should

be used. Reading differences of ^3 percent will produce a SINAD measurement

error of ±0.25 dB, whereas reading differences of ±1 percent will produce

errors less than ±0.1 dB.

Another error source is the noise and distortion caused by the power

amplifier. The value of distortion may be determined by using the distortion

analyzer to measure the distortion of the amplifier. The measurement is made

by setting the noise generator to its lowest level and setting the low

distortion oscillator to one of the amplitudes that are to be used in the

test. Then the distortion analyzer is set to the distortion mode and the

distortion level is noted. The indicated level must be at least 10 dB below

the lowest distortion level to be measured.

Finally, the presence of the signal from one generator while measuring

the level of the other wi T1 contribute an error. As stated above, the level

of the generator not being measured should be more than 20 dB below the level

of the signal being measured. At a ratio of 20 dB this will cause the level

of the signal being measured to be one percent high, which will contribute an error of less than 0.1 dB to the calculated SINAD level. If the ratio of the

signal levels cannot be kept at greater than a 20 dB difference, then a correction should be applied to account for this additional signal during the

measurement.

4.3.4 Residual Distortion and Noise

The lowest distortion level that the distortion analyzer can measure is

limited by the ability of the analyzer to lock onto and notch out (filter) the

fundamental signal frequency, and by the residual noise and distortion of the

internal circuitry. This test measures the latter two properties by presenting

a sine wave with low distortion to the distortion analyzer. The distortion of

the signal used in this test must be at least 10 dB below the level to which

the distortion analyzer is being qualified.

Measurement Technique

The residual distortion and noise test is very straightforward; figure 14

shows the test setup. The oscillator level is set with an ac voltmeter and

42
43

Test

setup

for

measuring

residual

distortion

and

noise

at

input

levels

above

10

volts

rms.

,
o

>>

ra3

cr . i- O) o

JZ 4J

-M fO CDr— C ••-

•I- u

CO 3 O

CO

IT3 C

OJ O

E T4-) i- s_ o o

4- -U

CO CL-.- 3 -O

4-> I OJ 2

CO O

+J

CO OJ

O) -!=

CD

C7>

44
the attendant distortion is read from the distortion analyzer. For higher

signal levels above 10 V rms, the power amplifier must be used as shown in

figure 15. For these tests a low pass filter is usually added to reduce the

higher frequency noise components contributed by the power amplifier. The

test for these voltage levels is the same as for the lower level.

Sources of Measurement Error

The main error sources are the characteristics of the low distortion

oscillator and the power amplifier. These devices must have the required low

distortion levels. If there is some question as to whether they are operating

properly, the distortion of these units can be measured. This requires a tunable notch filter, such as a Tektronix calibration fixture 067-0938-00, and

a spectrum analyzer. The test setup is shown in figure 16. The notch filter

is adjusted to remove as much of the fundamental as possible. The amplitudes

of the harmonics and the background noise level are then measured with the

spectrum analyzer. From the known amplitude of the fundamental, the

distortion of the oscillator or of the amplifier can be determined. The noise

floor of the spectrum analyzer must be taken into account as a limiting factor

in determining the distortion and noise characteristics of the source. The

spectrum analyzer should have a noise floor at least 10 dB below the specified

residual distortion and noise of the distortion analyzer under test.

4.4 FILTER CHARACTERISTICS

4.4.1 High Pass/Low Pass Filter Measurements

Audio distortion analyzers contain several sets of filters that are selectable by front panel controls. A high-pass filter can be used to reject

low-frequency components of the waveform presented to the audio analyzer.

Also, a choice of low pass filters is available to reject the high-frequency

components. These filters, used singly or in combination, may be used to

reduce unwanted signals and the effects of noise in the measurements made by

the audio distortion analyzer.

Filters are generally characterized by two parameters: the "corner frequency"

and the "rolloff" rate at which the signal is attenuated as a function of

frequency. The frequency response of a filter is conventionally represented

by a Bode plot. The absolute value of the voltage gain (or loss) measured at the output of the filter is plotted in dB versus the logarithm of the

frequency of the voltage source applied to the input of the filter. Typical

Bode plots of a high- and a low-pass filter are shown in figure 17.

The "corner frequency" is usually defined as that frequency where the

attenuation of the power is twice (-3dB) its midband value [6]. Such a definition agrees closely with the corner frequency as shown in figure 17.

In this figure, the corner frequency is defined as the intersection of the

straight-line extrapolation of the attenuated portion of the filter

characteristic with the extrapolated midband value.

45
NIVO a311ld

>

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z

m

D

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LUtr

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oc

LU

ILL

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<

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LU3

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o

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LU

H

Ul

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0. I

0

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(1) T3o

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46
It is important that the frequency response of the filters be defined for

measurement instruments such as an audio distortion analyzer. The filter

parameters, such as corner frequency and rolloff, determine the bandwidth of

the instrument when the filters are used.

Most audio distortion analyzers investigated had at least three switch-selectable filters. A 400-Hz high-pass filter can be inserted in the input path of

the ac signal before the notch filter to reject 60 Hz interference that may be

present on the signal to be measured. This 60 Hz interference is often a result of ground loops. In addition, two low-pass filters are provided which

limit the high-frequency response of the system to 30 kHz and 80 kHz,

respectively. These filters are provided to remove the high-frequency noise

components in low-frequency distortion and signal -to-noise measurements.

Measurement Technique

The same measurement method is used to characterize both the high- and

low-pass frequency filters. The method consists of applying a nominal one V ac (rms) signal to the input of the audio distortion analyzer from an oscillator set to the specified corner frequency of the filter under

investigation. The switches controlling the filters are set such that all

filters are out of the signal path. The amplitude of the signal is then

measured by the audio distortion analyzer and this amplitude is referenced to

be zero dB. To test the filter response at the minus three dB corner

frequency, the filter is then switched on. The frequency of the input signal

is adjusted so that the amplitude of the signal, -as measured by the audio

distortion analyzer, decreases by exactly three dB. The frequency of the

signal is then measured and recorded.

The slope of the filter character! Stic, or rolloff, is measured in a similar

manner. The filters are switched off and the amplitude of the input signal

is set to zero dB. The frequency of the input signal is changed by one decade

from the measured three dB corner frequency and the amplitude of the signal,

as measured by the audio analyzer in decibels, is measured and recorded. A

digital multimeter is used to measure the amplitude of the input signal at

both frequencies and the amplitude is adjusted, if necessary, to assure that

equal signal levels were applied to the audio distortion analyzer at both

frequencies. To determine character! sties of the low-pass filter, the

measurement of rolloff requires that the input signal frequency be increased

by one decade, or a factor of ten. Conversely, the signal frequency is

decreased by a factor of ten to determine the rolloff characteristics of the

high-pass filter. In either case, the change in output amplitude of the

filter is measured over a decade change in input frequency, referenced to the corner frequency.

Sources of Measurement Error

Possible sources of error in determining the filter character! sties include

errors in measuring the input signal frequency and amplitude, errors in the

measurement of the output amplitude of the filter by the audio distortion

analyzer, and measurement of signals outside the specified bandwidth of the

instrument.

47
The amplitude of the input signal is nominally set to 1.0 vac (rms). This

amplitude can be measured by a digital multimeter with a worse-case accuracy

of ±3.5 percent. This worse-case accuracy occurs when the digital multimeter

reads a voltage between 0.3 and 10 V ac (rms) at frequencies from 500 kHz to 1 MHz. This worse-case error is encountered in performing the 80 kHz low-pass

filter test (10.2.6.2). The ±3.5 percent error of applied voltage is

equivalent to a ±0.299 dB error in the determination of the filter slope

character! Stic.

The frequency' of the input signal is measured with a frequency counter.

Typically, frequency counters demonstrate the largest percentage error at low

frequencies, since their accuracy is determined by an uncertainty of plus or minus one count in the least significant digit. The lowest frequency

measured in these procedures is encountered in determining the high-pass

filter slope characteristic. This procedure requires the frequency

measurement of a 40 Hz signal. The least significant digit for the 40 Hz

measurement is 0.1 Hz. Thus, the frequency error from the one digit ambiguity

is one part in 400 or ±0.25 percent. The uncertainity of the amplitude of the

output of the filter is directly proportional to the frequency error; thus,

the uncertainity of the measured amplitude is

Amplitude Uncertainity = 60 dB/decade x 0.0025

= 0.15 dB/decade.

The measurement of the output signal from the filters is made by the

distortion analyzer in the amplitude measurement mode. Typically, distortion

analyzers display the amplitude of the input signal in either linear units

(volts ac rms) or logarithmic units (dB) relative to a signal level. In either case, the specified amplitude accuracy of the distortion analyzer

should be considered as a possible source of error in characterizing the

filters.

A further source of possible error is the measurement procedure. Some audio

distortion analyzers have a bandwidth of approximately 100 kHz. The test

procedure for the 80 kHz low-pass filter requires that an 800 kHz signal be

applied to the input of such analyzers in order to characterize the filter

slope over a one decade frequency change. Since the inherent bandwidth of the

distortion analyzer should attenuate such high-frequency input signals, it was deemed that this test is valid. However, users of this test should be aware that it may require operation of the audio distortion analyzer at frequencies

in excess of the required performance specifications.

48
5. References

[1] Fink, Donald D., Electronics Engineers Handbook, McGraw-Hill Book Co.,

New York, NY, First Ed. 1970, p. 13-6.

[2] The Institute of High Fidelity, Inc., Stand. Methods of measurement for

Audio Amplifiers, The Institute of High Fidelity, Inc., NY (1978) p. 9.

[3] Fink, Donald, D., Electronics Engineers Handbook, McGraw-Hill Book Co.,

New York, NY, 1st Ed. 1970, p. 22-67.

[4] The International Telegraph and Telephone Consultative Committee

(C.C.I.T.T.) Fifth Plenary Assembly, 1972 Telephone Transmission

Quality, The International Telecommunication Union (1973), pp. 87-91.

[5] IEEE Standard Dictionary of Electrical and Electronics Terms, John Wiley

& Sons, Inc. 2nd Ed.

[6] Hunter, Lloyd P., Handbook of Semiconductor Electronics, McGraw-Hill Book

Co., Inc., New York, NY 3rd Ed. 1970, pp. 12-24.

49

APPENDIX A

PEFORMANCE SPECIFICATION FOR

TS- 4084 ( ) /G

DISTORTION ANALYZER

Note :

These specifications were written by the U.S. Army Communications Electronic

Cornmand (CECOM) and have been reprinted exactly as presented to NBS by the

Army.

A-1
SPECIFICATiai FOR TS-4084 ( )/G

A. REQUIRH’lENTS

1. Safety. Unless otherwise specified herein, the equipment shall conply

with the Type II safety requirements specified in MIL-T-28800C.

1.1 Personnel Hazardr.. Personnel hazards shall fc>e kept to a minimum.

The criteria of MIL-T-28800C, uhall be made applicable for tasks cind efforts

such as the selection of parts, the corplete manufacturing and assembly process,

cind any product baseline conf ii_!uration changes that may be inplemented during

the course of the contract. Verification that carpliance with this requirement

has been achieved shall be tliruugh a visual inspection (see 1.5).

1.2 Edge Rounding Exrosed. Exposed edges and corners shall be rounaed

sufficiently to minimize laceration/puncture hazards, tlie design goal being a minimum radius of 0.04 inch (1 irm) for edges and a minimum of 0.5 inch (12.7 mm)

for corners.

1.3 Radioactive Materials. Radioactive materials shall not be used

(e.g., luminous dials/mark ings, electron tubes, surge arrestors and lenses).

1.4 Weight Caution Label. All equipments over 35 pounds shall have a

v;eight caution Iqbel for Two-P-jrson Lift centered at tine top surface. The format and color code shall be in accordance with American National Standards

.Institute (AMSI) Standard Z35. ’’.-1972. Label size shall be appropriate for high

visibility and legibility. Marking requirements shall conform to MIL-M-13231.

The v^eight caution label should read, for exanple:

CAUTION

* Pounds

IWO-PERSON LIFT

* Weight of Distortion Analyzer

1.5 Systgn Safety En<:;ineerinq Inspection. A visual inspection shall

be performed in the presence o£ a government safety representative to determine

tliat all requirenents of 1, l.L, 1.2, 1.3 and 1.4 have been incorporatea in the

equipment. Inability to meet these requirements shall constitute a failure of

the test. Result of this insp3ction shall be included in the Safety Assessment

Report (DI-H-7049) if required in the contract.

2. Design and Construction. Unless otlierwise specified herein, the equipment shall comply with the Type II, Class 5, Style E, Color R, design and

construction requirements of MIL-T-28800C. All requirements v\tiich are autematically invoked by MIL-T-28800C to all tyr^es, and specifically to Type II, apply.

2.1 Front Handles. Front handles or a front panel cover shall be provided on tlie equipment which can be used for carrying the equipment and will

offer a degree of protection to the front panel controls.
2.2

Racicnount. Rackniounting capability shall be available.

2.3 Mainframe Plug-Ir> Concept. Equipment utilizing externally

accessible, removeable subassemblies (mainframe plug-in concept) does not meet

the requirements of this specil ication if more than one plug-in is used.

2.4 Controls. All a^ntrols required to operate the equipment

throughout its specified perfoimance range shall be located on the front panel.

3. Parts, Materials, and Processes. Unless otherwise specified herein, the

equipment shall comply with Tyi^e II parts, materials, and processes requirements

of MIL-T-2880(X:.

3.1 Restricted Material. Equipment shall comply with the restricted

material requirements of MIL-T--28800C including the requirement for radioactive

deterioration of -any material contained in the equipment due to effects of

outgassing.

3.2 Interchanqeabili^ry. Unless otherwise specified herein, the equipment shall ccmply with Type II interchangeability requirements of MIL-T-28800C.

3.2.1 Marking. All replaceable assenblies, subassemblies, modules and

printed circuit card assemblies shall be indelibly marked with tiie contractor's

Federal Supply Code for Manufacturers (FSQ-1) and the contractor's part number.

4. Marking and Identification. Unless otherwise specified herein, tne

equipment shall canply with Tyi:)e II marking and identification requirements of

MIL-T-2880CX:.

4.1 Supplemental Identification Plate. .The supplemental identification plate specified in MIL-T-28800C shall contain the follov;ing data:

a. Ncmenclature

b. Contract Number

c. Serial Number

d. National stock number

e. US

4.2 Information Plate. An information plate affixed to each deliverable equipment shall contain the following data:

a. Warranty termination date.

b. Brief statonent of warranty limitations (for example: opening a cover voids warranty; calibration adjustments may be made without voiding

warranty; defective modules may be returned for warranty service; etc.).

4.3 Battery Warning Label. Equipment containing batteries shall provide a battery warning label in accordance with MIL-T-28800C, para 3. 8. 3. 1.3.
b. Electrical Pa-/er Sources. Unless otherwise specified herein, the

equipment shall coiroly with the Type II electrical power sources and connections

requirements of I^L-T-28800C. The equipment shall operate from a nominal 115

VAC, single phase 50, 60 and 400 Hz and 230 VAC, 50 and 60 Hz power source.

5.1 Fuses and Circuit Breakers. Fuses or circuit breakers shall be in

accordance with MIL-T-28800C. Either common or separate fuseholders may be 'provided. If only one fuseholder is used (ccmmon) , tiie equipment shall be provided

v/ith tlie 115 VAC fuse installec; and the 230 VAC fuse shall be provided v/ith the

accessories.

5.2 Electrical Power Connections. The equipment shall be delivered

connected for 115 VAC 60 Hz ration.

6. Accessories . The following accessories shall be supplied with each

equipment:

a. Power Cable

b. Fuses (See Para 5 1) c. One operator's manual

d. All cables eind adaptors necessary for initial turn on or preoperational check.

e. Other standard aa'essories, if any, that are offered commercially.

7. Preconditioning Reaui’'ement (Burn-In)

.

Each deliverable equipment

shall be subjected to a minimun 48 hours on-time burn-in period, prior to

Acceptance Testing. During the last 24 hours of on-time burn-in, the equipment

must operate failure free. Up until this time, equipment will be allcv;ed to

accumulate failures. Each equipment v^hich fails during the final 24-hour period

shall be repaired and returned to test until it successfully survives a 24-hour

period without failure. Failures which occur during the burn-in test shall be

noted and reported, but shall not count toward tlie establisliment of equipment

MTBF. Prior to burn-in, the Satisfactory Operation Test (SOT) shall be conducted. Daily Satisfactory Operation Checks (SOC) shall be conducted. For the

last 24-hour failure-free period, a complete satisfactory operation test shall

be conducted prior to and after the period. The SOC and SOT are defined by

MIL-T-28800C, Paras 6.3.2.24 and 6.3.2.25. Wiile under burn-in tlie equipment

shall be subjected to the following conditions:

Ambient temperature: 40*C +5’C -O'C

Input Voltage: Ncmin-il specified voltage +5% -2%

Equipment on-off cycling: Equipment on for 8 hours and off for 4

hours. This cycle shall continue until a minimum 48 hours on time is accumulated, with the last 24 hours of on time, failure free.

8. Environmental Requirements. Unless otlierwise specified herein, the

equipnent shall ccmply with the Class 5 environmental requirements of

MIM-28800C.
8.1 Vibration. The <>quipment shall conply witii Class 5 vibration

requirements of KIL-T-28000C, except that the equipment is not required to be

operating during tlie vibration test.

8.2 Electranaqnetic Interference (EI-U). EMI requirements shall be as specified in MIL-T-28800C and MIL-STI>461A Notice 4 (EL) except as noted below.

The equipment shall comply witii the foilaving enission and susceptibility

requiren'.ents vstien tested as spoified in Para 8.3.

CE02 CS02 REOr RS03

CE04 CS06 REO; .1

8.2.1 Radiated Emission RE02.1. The narrow band emissions level shall

be as specified in MIL-GTD-461A Notice 4 (EL) over the 14 KHz to 1 GHz frequency

range.

8.2.2 Radiated Susceptibility RS03. The susceptibility shall be 1 V/m

over the 14 KHz to 1 GHz frequu^ncy range. The susceptibility limit shall be met

for both horizontally and vertically polarized fields.

8.3 EMI Testing. EMT testing shall be in accordance with MIL-T-28800C

and MIL-STD-462 Notice 3 (EL)

.

9. RAT4 Requirements .

9.1 Reliability Requirements. The equipment shall comply witli tiie

Type II Reliability Requirements of MIL-T-28800C, (Para 3.10.12 and Para

4. 5. 8. 1.2). • The contractor shall demonstrate his equiptrient MTEF (Oo) as stated

in his bid data submission. The stated value siicill be equal to or greater than

a ^^^DF (Oo) of 1500 hours. Reliability tests shall be performed on the first

production lot only.

9.2 Calibration. Calibration interval shall meet or exceed 240 days

with 85% of itsns still within tolerance at the end of the period.

9.3 Maintainability Requirements. The contractor shall demonstrate

his equipment mean-time-to-repair (f-flTR) (Ho in MIL-STD-471) , as stated in his

bid data suI:mission. The stated yalue shall be less than or equal to MTTR (Ho)

of 300 minutes. The maximum iiolerable MTTR (HI of MIL-STD-471) shall be 360

minutes. The MTTR shall include all the time required to troubleshoot, fault

isolate, repair and test the (equipment for any malfunction dcuvn to the lowest

circuit card or module level c:f the equipment, but does not include calibration

time. In equipments, sections of equipments or plug-ins (see para 2.3) not utilizing a modular concept, MTIR shall include all tune required to troubleshoot,

fault isolate, repair and test the equipment for any malfunction down to the

lowest discrete cenponent (resistor, switch, transistor, integrated circuit, nonrepairable assembly, and so forth) of the equipmient, but does not incluae

calibration time.

10. Performance. Unless otherwise noted, the following performance

requirements apply to the basic equipment after one hour warm-up for performance

across the full specified bandwidth and voltage range.
10.1 Operation. In measuring level and in measuring distorticai in

which the distortion is pure hanroiic distortiOT, and v^en the input signal to

noise and distortion ratio is greater than 20 d3 the equipment shall have full

automatic operation. There shall be no manual operations in locating the fundamental frequency, nulling the fundamental frequency and in locating the level.

For distortion measurements in v^ich the input signal to noise and distortion

ratios is less than 20 dB, down to 6 dB, the following is allowable: setting the

frequency of the distortion analyzer to within + 10% of the frequency of the

fundamental ccnponent of the input signal so that the analyzer can lock onto

and null the fundmental ccmpcffient of the input signal and remain locked down to

6 dB; or by inputing to the analyzer a signal in which the input signal to

noise and distortion ratio is greater than 20 dB so that the distortiai analyzer

can lock aito and null the fundamental corpOTent of the input signal and remain

locked down to 6 dB.

10.1.1 Distortioi Measuranent. The distorticn analyzer shall measure

total harmonic distortion and noise (herein called distortiOTi) by dividing the

distortion plus noise over the input signal.

10.2 Distortion/Voltmeter/SINAD Mode. The following specifications

apply to the equipment in the distortion, voltmeter and SINAD mode.

I 10.2.1 Display. The display shall be a 3*s digit electronic digital

display, calibrated to measure level in dBm, rms volts and millivolts, distortion in dB and %, and sinad in dB. i

i 10.2.1.1 Display Resolutiai. The resoluticn of the display in

measuring level in dBm, distortion in dB and %, and sinad in dB shall be 0.1

units or less. For measuring level in millivolts and volts display shall i display at least 100 counts. >

10.2.2 Input Connector. The input to the equipment shall be capable

of providing a differential input for signals less than 1 volt rms. For signals J greater than 1 volt rms the input connector may be a full differential input or single ended. The equipment must be protected, such that no internal caiponents

need be replaced (i.e., the cover of equipment shall not be removed), to the

range specified in 10.4.1 for any inprcper cOTinection to the equipment. Input [ connector may be BNC female coaxial cOTinector or dual bananna. If dual

bananna, a BNC to dual bananna adapter must be provided with each equipment.

5 10.2.3 Monitor Output Connector. There shall be an output connector

located on the front panel which when the equipment is in the A.C. voltmeter

mode provides a scaled output .of the input signal and in the distortion and ii| SINAD mode provides a scaled output of the input signal with the fundamental j removed. The output level shall be greater than 50 millivolts r^is accurate to

within _+ 10% and less than 5 volts rms, accurate to within ^ 10%. The output

signal shall not be clipped for input signals with crest factors from 1:1 to b 3:1.

10.2.3.1

Output Impedance. The output impedance for the output connector shall be 600 ohms accurate to within jf 5%.

10.2.4 Detection. The analyzer shall be capable of detecting input

signals by true rms detection (distorticn, SINAD and voltmeter mode) on signals

with crest factor from 1:1 to 3:1 and also shall be able to detect signals by

average detection (distortion and SINAD mode) . Type of detection shall be

selectable by either a pushbutton or dial located on the front panel.

A-6
10.2.5 Response Tiine. Hie response time over the entire specified

performance range of the equipment shall be less than 10 seconds to obtain a

reading within the accuracies as stated in para 10.3.4 and 10.4.2 and stable to

within + 3 counts of the 0.1 digit.

10.2.6 Filters. Ihere shall be 3 internal filters selectable by

controls cn the front panel.

10.2.6.1 Low Pass Filter. 3 dB at 30 KHz accurate to within + 2 KHz

and a rolloff of at least 60 dB/decade (18 dB/octave). ~

10.2.6.2 Low Pass Filter. 3 dB at 80 KHz accurate to within + 4 Kiz

and a rolloff of at least 60 dB/decade (18 dB/octave)

.

10.2.6.3 High Pass Filter. 3 dB at 400 Hz accurate to within + 40 Hz

and a rolloff of at least 60 dB/decade (18 dB/octave) . ~

10.2.6.3.1 Line Frequency Rejection. The high pass filter shall

reject line frequency interference at least 40 dB.

10.2.7 Mode Selecticn. The front panel shall include ccntrols to

select mode of operaticn (distortion, SH®D or voltmeter)

,

10.2.8 Canrai Mode Rejection Ratio (01RR)

.

For a common mode signal

of < 1 volt rms, the oorrmcn mode rejection ratio in the frequency range frcra 50

Hz to 800 Hz, s^ll be greater than 40 c^.

10.2.9 Overload Protection, 'flie instrument shall be protected to at

least a rms value of 175 volts and shall be capable of performing to all

specifications after being subjected to an overload voltage up to 175 volts rms.

10.2.10 Relative dB Reference . The equipment shall be capable of setting a measurement made in dB and dBm as a zero reference. The control to set the dB

reference shall be located on the front panel.

10.2.11 Bandwidth. The 3 dB bandwidth of the equipment shall be at

least 300 KHz.

10.2.12 Input Impedance. The input inpedance shall be 100 K ohms

accurate to within + 2% shunted by less than 300 picofarads.

10.2.13 Fundamental Frequency Locking . There shall be an indication

on the front panel as to when the distortion analyzer is locked cn the fundamental conpcnent of the input signal.

10.3 Distortion/SINAD Mode. The following specifications apply to the

equipment operating in the distortion and SINAD mode.

10.3.1 Fundamental Frepfuency Range. The equipment shall cover the

fundamental frequency range from 20.0 Hz to 100.0 KHz.

10.3.2 Input Level Range. The minimum input level range for distortion and SINAD measurements shall be from 100.0 millivolts rms to 130.0 volts

rms.

A7
10.3.3 Distortion Measurement Range. The equipnents distortiai

measuronent range shall cover, within specified accuracy, the range fran 0.1%

(-60 dB) to 50% (-6dB)

.

10.3.4 Distortion Measurement Accuracy. The at^uracy of the distormeasursnent across the full bandwidth and voltage range shall be within the

following:

Fundamental Frequency Range Accuracy

20 Hz - 20 KHz ± 1

20 KHz - 50 KHz + 2 dS

50 KHz - 100 KHz +3 dB, -4 dB

10.3.5 SINAD Measurement. Using average detection, the equipment

shall be capable of measuring and displaying SINAD over the entire frequency and

voltage rangeas specified herein, in the range from 6 dB to 60 dB.

10.3.6 SINAD Measurement Accuracy. The accuracy of the SINAD measurement shall be within the same accuracy as spjecified in para 10.3.4.

10.3.7 Fundamental Rejection. The distortiai analyzer shall reject the

fundamental ccnpaient of the input signal by at least 10 dB below the total harmonic distortion and noise level.

10.3.8 Measurement Mode. The equipment shall display distorticxi in

dB and % and sinad in dB. Measurement mode shall be selectable by front panel

cOTtrol.

10.3.9 Residual Distortion and Noise. Without using any filters, for

both rms and average response, the total harmonic distortion + noise introduced

by the equipment across the entire voltage range shall be less than -65 dB

(.056%) across the entire bandwidth of the equipment.

10.3.10 Level Underrange/Overrange Indicaticn. There shall be on the

front panel an indication to indicate when the input signal is not within the

accuracies as specified in para 10.3.4.

10.4 Voltmeter. The following specifications apply to the equipment

operating in the A.C. voltmeter mode.

10.4.1 Voltage Range. The minimum range of the A.C. voltmeter shall

be from 100 millivolts true rms to 130 volts true rms.

10.4.2 Voltmeter Accuracy. The A.C. voltmeter shall be accurate, over

the entire range as specified in para 10.4.1, to within _+ 2% of the reading in

the fundamental frequency range of 20 Hz to 20 KHz, and within 4% of the

reading in the fundamental frequency range from 20 KHz to 100 KHz.

10.4.3 Measurement Mode. The equipment shall display level in rms volts, millivolts, and dBm (into 600 ohms). Measurement mode shall be selectable by frOTt panel control.
10.4.4 Level Overrange Indicaticai. There shall be on the froit panel

an indication to indicate when the input signal is not within the accuracies as specified in para 10.4.2.

11. Digital Interface. An IEEE STANDARD 488-1978 interface shall be

provided. The interface shall provide talk and listen for all equipment functions required by this specification with the exceptic^i of line power on and

off. The interface shall be furnished with address selecticais from 00 to 30 and

interface functions SHI, AHl, SRI, RLl, PRO, DCl, DTO, CO and aie of Tl, 2, 5, 6

and one of LI, 2, 3, 4. Mating COTnector to be in accordance with i STD

488-1978, Chapter 4, without the use of removeable adapter or converters.

APPENDIX B

TEST PROCEDURES

for

SPECIFICATION PARAGRAPHS

10.1 through 10.4.4

The data sheets and tables referred to in this Appendix

are located in Appendix C.

Note :

The procedures described in this document are valid only if used with test

equipment that is maintained within the normal Army calibration procedures.

Certain commercial equipment is identified in this document. This

identification does not imply endorsement by the National Bureau of Standards

nor does it imply that the equipment identified is necessarily the best

available for the purpose. Also, each specification description included with

these procedures have been copied without modification from the specification

paragraphs in Appendix A.

B-1
10.1 OPERATION

Specification:

In measuring level and in measuring distortion in which the distortion is pure

harmonic distortion, and when the input signal to noise and distortion ratio

is greater than 20 dB, the equipment shall have full automatic operation.

There shall be no manual operations in locating the fundamental frequency,

nulling the fundamental frequency and in locating the level. For distortion

measurements in which -the input signal to noise and distortion ratios is less

than 20 dB, down to 6 dB, the following is allowable: setting the frequency

of the distortion analyzer to within ±10% of the frequency of the fundamental

component of the input signal so that the analyzer can lock onto and null the

fundamental component of the input signal and remain locked down to 6 dB; or by inputing to the analyzer a signal in which the input signal to noise and

distortion ratio is greater than 20 dB so that the distortion analyzer can

lock onto and null the fundamental component of the input signal and remain

locked down to 6dB.

Equipment:

Manuf acturer ' s manual for unit under test (OUT)

Procedure :

1. Read the manuals for the UUT and note'whether or not any manual operations

are required to. locate the fundamental frequency or signal level during any of

the tests covered by this test procedure.

B-2
10.1.1 DISTORTION MEASUREMENT

Specification :

The distortion analyzer shall measure total harmonic distortion and noise

(herein called distortion) by dividing the distortion plus noise over the

input signal.

Equipment :

Manuf acturer ' s manual for UUT

Procedure :

1. Read the manual for the UUT and assure that the equipment measures total

harmonic distortion by dividing the distortion plus noise over the input

signal. Note on the data sheet whether or not this condition is met.
10.2.1 DISPLAY

Specification :

The display shall be 3 1/2 digit electronic digital display, calibrated to

measure level in dBm, rms volts and millivolts, distortion in dB and %, and

SINAD in dB.

Equipment :

Manufacturer's manual for UUT

Procedure :

1. Read the manual for the UUT. Assure that the UUT contains a 3 1/2 digit

digital display calibrated to display level in dBm, rms volts and millivolts,

distortion in dB and %, and SINAD in dB.
10.2.1.1 DISPLAY RESOLUTION

Specification:

The resolution of the display in measuring level in dBm, distortion in dB and

and SINAD in dB shall be 0.1 units or less. For measuring level in

millivolts and volts display shall display at least 100 counts.

Procedure :

1. Set the controls on the UUT such that the instrument measures input level

in dBm. Turn the autoranging feature of the UUT to the OFF position.

2. Set the range of the UUT to each range possible.

3. Note and record the minimum resolution indicated on the display of the UUT

on the data sheet.

4. Set the controls on the UUT such that the instrument measures input level

in volts. Turn the autoranging feature of the UUT to the OFF position.

5. Set the range of the UUT to each range possible.

6. Note and record the minimijn number of counts indicated on the display of

the UUT on the data sheet.

« 7. Set the controls on the UUT such that the instrument measures distortion

in dB. Turn the autoranging feature of the UUT to the OFF position.

8. Set the range of the UUT to each range possible.

9. Note and record the minimum resolution indicated on the display of the UUT

on the data sheet.

10. Set the controls on the UUT such that the instrument measures distortion

in percent. Turn the autoranging feature of the UUT to the OFF position.

11. Set the range of the UUT to each range possible.

12. Note and record the minimum resolution indicated on the display of the

UUT on the data sheet.

B-5
10.2.2 INPUT CONNECTOR

Specification

:

The input to the equipment shall be capable of providing a differential input

for signals less than 1 volt rms. For signals greater than 1 volt rms the

input connector may be a full differential input or single ended. The

equipment must be protected, such that no internal components need be replaced

(i.e., the cover of the equipment shall not be removed), to the range

specified in 10.4.1 for any improper connection to the equipment. Input

connector may be BNC female coaxial connector or dual banana. If dual banana,

a BNC to dual banana adapter must be provided with each equipment.

Procedure :

1. Assure that the UUT is capable of providing a differential input for

signals less than 1 V ac (rms) by performing measurements required in

paragraph 10.2.8. Note on data sheet if this condition is met.

2. Assure that the UUT is protected, such that no internal components need be

replaced (i.e., the cover of the equipment shall not be removed), to the range

specified in 10.3.2 for any improper connection in paragraph 10.2.9. Note on data sheet if this condition is met.

3. Visually inspect the UUT to determine if the input connector is a BNC

female coaxial connector or dual banana connector. Note on data sheet which

connector is present. Note on data sheet if a BNC to dual banana adapter i-s provided if the inpuf connector is a dual banana.

B-6
10.2.3 MONITOR OUTPUT CONNECTOR

Specification:

There shall be an output connector located on the front panel which when the

equipment is in the AC voltmeter mode provides a scaled output of the input

signal and in the distortion and SINAD mode provides a scaled output of the

input signal with the fundamental removed. The output level shall be greater

than 50 millivolts rms accurate to within ±10% and less than 5 volts rms,

accurate to within ±10%. The output signal shall not be clipped for input

signals with crest factors from 1:1 to 3:1.

10.2.3 Part 1. Sine Wave Test Signals

Equipment:

Items

AC Calibrator

Power Amplifier

AC Voltmeter

Range

100 mV to 100 V ac 100 V to 175 V ac 10 mV to 175 V ac

Procedure:

1. Connect the equipment as shown below

Model

Fluke 5200A

Fluke 5205A

Fluke 8506A

or equivalent

or equivalent

or equivalent

Fig. 10.2.3A. Test setup for measuring the accuracy of the monitor

output for sine wave signals.

B-7
2.

Set the UUT controls as follows:

On/Off switch

Function

Filters (all)

Range Mode

ON

AC LEVEL MODE

OFF

AUTORANGE

3.

Set the voltmeter controls as follows:

Function AC VOLTS

Mode HIGH ACCURACY

Range AUTO

4. Refer to data sheet table 10.2.3A for setting AC calibrator frequency and

amplitude levels.

5. Read and record the AC voltmeter reading for each line of data. Note that

for calibrator amplitude levels greater than 100 volts the equipment is to be

reconnected as shown below.

Fig. 10.2.3B. Test setup for measuring the accuracy of the monitor

output for high voltage sine wave signals.

6.

Calculate the deviation in percent for each line of data using the 1 kHz

ac voltmeter indication for each group of three measurements at the same amplitude as the reference level.

B-8
10.2.3 Part 2. 3:1 Crest Factor Test Signals

Equipment :

Items Range Mode

AC Voltmeter

Arbitrary Waveform Generator

488 Controller

Osfi 1 loscope

Power Amplifier

10 mV to 175 V ac 20 Hz to 20 kHz

20 Hz to 300 kHz

100 V to 130 V ac

Fluke 8506A or equivalent

Wavetek 275 or equivalent

HP 9836 or equivalent

Tektronix 2445 or equivalent

Fluke 5205A or equivalent

Procedure :

1. Connect the equipment to the OUT as shown below

Fig. 10.2.3C. Test setup for measuring the monitor response to

signals with a 3:1 crest factor and peak amplitudes

less than 10 volts.

2. Set the OUT Controls as follows:

Function

Filters (all)

Range Mode

AC LEVEL MODE

OFF

AUTORANGE

B-9
3.

Set the controls on the voltmeter as follows:

Function AC VOLTS

Mode HIGH ACCURACY

Range AUTO

4. Set the frequency of the arbitrary waveform generator to 20 Hz and set its

amplitude off.

5. Set the amplitude of the arbitrary waveform generator to indicate 100 mV

on the ac voltmeter.

6. Adjust gains and appropriate sweep settings on the oscilloscope so that

the trace of the input and monitor output signal can be compared.

7. Observe if there is any clipping on the monitor output signal and note on data sheet Table 10.2.3B.

8. Repeat steps 5 through 7 for input levels to the UUT of IV, lOV, lOOV,

and 130V. The ac voltmeter is used to set the input levels. Note that when

the peak-to-peak, voltage requirement exceeds 10 volts reconnect the equipment

as shown below. NOTE: Extreme caution must be used when the power amplifier

is operational.

Fig. 10.2. 3D. Test setup for measuring the monitor response to

signals with a 3:1 crest factor and peak amplitudes

greater than 10 volts

.

9.

Set the frequency of the arbitrary waveform generator to 20 kHz and repeat

steps 5 through 8 inclusive.

B-10
10.2.3.1 OUTPUT IMPEDANCE

Specification:

The output impedance for the output connector shall be 600 ohms accurate to

within ±5%

Equipment

:

Items Range

Audio Oscillator 10 Hz to 1 MHz

AC voltmeter

600 ohm Feedthrough Termination, ±1%

Model

TEK FG504T, or equivalent

Fluke 8506A, or equivalent

TEK 011-0092-00, or equivalent

Procedure :

1. Connect the equipment as shown below

(Insert in step 6)

Fig. 10.2.3.1. Test setup for measuring the monitor output impedance.

2. Set the controls on the UUT as follows:

Function AC LEVEL MODE

Filters (all) OFF

Range AUTORANGE

B-1

1
3.

Set the Voltmeter controls as follows:

Function

Mode

Range

AC VOLTS

HIGH ACCURACY

AUTO

4. Set the frequency of the audio oscillator to approximately 1000 Hz as indicated by the dial setting. Adjust the amplitude of the audio oscillator

such that the voltmeter indicates a nominal value of 1.0 V ac (rms).

5. Measure and record the voltage indicated on the AC voltmeter as VI.

6. Disconnect the cable from the voltmeter to the UUT at the output connector

of the UUT. Connect the feedthrough termination to the output connector.

Reconnect the cable to the voltmeter to the feedthrough termination.

7. Measure and record the voltage indicated on the digital voltmeter as V2.

8. Calculate the output impedance by the following formula:

Rout = (600 V1/V2) - 600.

9. Record the value of Rout 0*^ <^3ta sheet.

B-12
10.2.4 DETECTION

Specification ;

The analyzer shall be capable of detecting input signals by true rms detection

(distortion, SINAD and voltmeter mode) on signals with crest factor from 1:1

to 3:1 and also shall be able to detect signals by average detection

(distortion and SINAD mode). Type of detection shall be selectable by either

a pushbutton or dial located on the front panel.

Equipment :

Manufacturer's manual for UUT.

Procedure:

1. Read the manual for the UUT and note what type of detection (average or rms) is used for each mode. Assure that both modes of detection are selectable from the front panel. Record on the data sheet the modes of

detection.

B-13
10.2.5 RESPONSE TIME

Specification:

The response time over the entire specified performance range of the equipment

shall be less than 10 seconds to obtain a reading within the accuracies as stated in para. 10.3.4 and 10.4.2 and stable to within ±3 counts of the 0.1

digit.

Procedure :

1. The response time in the voltmeter mode is checked at the 20Hz, 0.1 volt

level in steps 28 through 30 of the procedure in 10.4.2.

2. The response time in the distortion mode is checked at the 20 Hz,

0.1 volt, 60 dB level in steps 12 through 15 of the procedure in 10.3.4.

3. In each of the response time tests record the time required to obtain a reading that is stable within ±3 counts at the 0.1 digit.

B-14
10.2.6 FILTERS

Specification :

There shall be 3 internal filters selectable by controls on the front panel.

Procedure :

Assure that the UUT has at least 3 internal filters which are selectable by

controls on the front panel. Note on data sheet if this condition is met.

B-15
10.2.6.1 LOW PASS FILTER

Specification :

3 dB at 30 kHz accurate to within ±2 kHz and a rolloff at least 60 dB/decade

( 18dB/octave)

.

Equipment :

Items ’ Range

Audio Oscillator 10 Hz to 1 MHz

AC Voltmeter

Frequency Counter

600 ohm Feedthrough Termination, ±1%

Model

Tek FG504T, or equivalent

Fluke 8506A, or equivalent

HP 5316A, or equivalent

TEK 011-0092-00, or equivalent

Procedure :

1. Connect the equipment as shown below

Fig. 10.2.6.1 Test setup for measuring the low pass filter (30 kHz)

response.

2. Set the controls on the AC voltmeter as follows:

Function AC VOLTS

Mode HIGH ACCURACY

Range AUTO

B-16
3. Set the frequency of the audio oscillator to 30 kHz as indicated by the

frequency counter. Adjust the amplitude of the audio oscillator such that the

voltmeter indicates nominally 1.0 V ac. Read and record on the data sheet the

actual voltage level.

4. Set the controls on the UUT as follows:

Filters (all) OFF

Ratio OFF

5. Select the dB RATIO on the UUT and, if provided, depress the PUSH TO SET 0

dB REF and set the LIN/LOG mode to LOG mode.

6. Select the 30 kHz filter on the UUT.

7. Adjust the frequency of the audio oscillator such that the display on the

UUT indicates -3.0 dB.

8. Read and record on the data sheet the frequency indicated on the frequency

meter.

9. Set the frequency to 300 kHz as indicated on the frequency meter.

10. If necessary, readjust the output amplitude of the audio oscillator such

that the AC voltmeter indicates the same voltage level as was obtained in step

3, above.

11. Read and record on the data sheet the dispTay indicated on the UUT. If

the UUT is capable of displaying voltage levels in dB, record the value

indicated. If the UUT is not capable of displaying the voltage level in dB,

calculate and record the rolloff for one decade change in frequency in dB,

using:

Rolloff (dB) = 20 log (Indicated Voltage / Input Voltage)

Where: the Input Voltage is that voltage indicated on the voltmeter

(step 10), and

the Indicated Voltage is that voltage read on the UUT (step 11).

B-17

1

I
10.2.6.2 LOW PASS FILTER

Specification:

3 dB at 80 kHz accurate to within ±4 kHz and a rolloff at least 60 dB/decade

(18 dB/octave).

Equipment :

Items Range

Audio Oscillator 10 Hz to 1 MHz

AC Voltmeter

Frequency Counter

600 ohm Feedthrough Termination, -1%

Model

TEK FG504T, or equivalent

Fluke 8506A, or equivalent

HP 5316A, or equivalent

TEK 011-0092-00, or equivalent

Procedure :

1. Connect the equipment as shown below

Fig. 10.2.6.2. Test setup for measuring the low pass filter (80 kHz)

response.

2. Set the controls on the AC voltmeter as follows:

AC VOLTS

HIGH ACCURACY

AUTO

Function

Mode

Range

B-18
3. Set the frequency of the audio oscillator to 80 kHz as indicated by the

frequency counter. Adjust the amplitude of the audio oscillator such that the

voltmeter indicates nominally 1.0 V ac (rms). Read and record on the data

sheet the actual voltage level.

4. Set the controls on the UUT as follows:

Filters (all) OFF

Ratio OFF

5. Select the dB RATIO on the UUT and, if provided, depress the PUSH TO SET 0

dB REF and set the LIN/LOG mode to LOG mode.

6. Select the 80 kHz filter on the UUT.

7. Adjust the frequency of the audio oscillator such that the display on the

UUT indicates -3.0 dB.

8. Read and record on the data sheet the frequency indicated on the frequency

meter.

9. Set the frequency to 800 kHz as indicated on the frequency meter.

10. If necessary, readjust the output amplitude of the audio oscillator such

that the AC voltmeter indicates the same voltage level as was obtained in step

3, above.

• 11. Read and record on the data sheet the display indicated on" the UUT. If

the UUT .is capable of displaying voltage levels in dB, record the value

indicated. If the UUT is not capable of displaying the voltage level in dB,

calculate and record the rolloff for one decade change in frequency in dB,

using:

Rolloff (dB) = 20 log (Indicated Voltage / Input Voltage)

Where: the Input Voltage is that voltage indicated on the voltmeter

(step 10), and

the Indicated Voltage is that voltage read on the UUT (step 11).

B-19
10.2.6.3 HIGH PASS FILTER

Specification :

3 dB at 400 Hz accurate to within ±40 Hz and a rolloff at least 60 dB/decade

(18 dB/octave).

Equipment:

Items Range Model

Audio Oscillator 10 Hz to 1 MHz TEK FG504T, or equivalent

AC Voltmeter

Frequency Counter

600 ohm Feedthrough Termination, ±1%

Fluke 8506A, or equivalent

HP 5316A, or equivalent

TEK 011-0092-00, or equivalent

Procedure :

1. Connect the equipment as shown below

Fig. 10.2.6.3 Test setup for measuring the high pass filter (400 Hz)

response.

2. Set the controls on the AC voltmeter as follows:

AC VOLTS

HIGH ACCURACY

AUTO

Function

Mode

Range

B-20
3. Set the frequency of the audio oscillator to 400 Hz as indicated by the

frequency counter. Adjust the amplitude of the audio oscillator such that the

voltmeter indicates nominally 1.0 V ac (rms). Read and record on the data

sheet the actual voltage level.

4. Set the controls on the UUT as follows:

Filters (all) OFF

Ratio OFF

5. Select the dB RATIO on the UUT and, if provided, depress the PUSH TO SET 0

dB REF and set the LIN/LOG mode to LOG mode.

6. Select the 400 Hz filter on the UUT.

7. Adjust the frequency of the audio oscillator such that the display on the

UUT indicates -3.0 dB.

8. Read and record on the data sheet the frequency indicated on the frequency

meter.

9. Set the frequency to 40 Hz as indicated on the frequency meter.

10. If necessary, readjust the output amplitude of the audio oscillator such

that the digital voltmeter indicates the same voltage level as was obtained in

step 3, above.

11. Read and record on the data sheet the display indicated on the UUT. If

the UUT is capable of displaying voltage levels in dB, record the value

indicated. If the UUT is not capable of displaying the voltage level in dB,

calculate and record the rolloff for one decade change in frequency in dB,

using:

Rolloff (dB) = 20 log (Indicated Voltage / Input Voltage)

Where: the Input Voltage is that voltage indicated on the voltmeter

(step 10), and

the Indicated Voltage is that voltage read on the UUT (step 11).

3-21
10.2.6.3.1 LINE FREQUENCY REJECTION

Specification :

The high pass filter shall reject the line frequency interference by at least

40 dB.

Equipment ;

Items Range

Audio Oscillator 10 Hz to 1 MHz

AC Voltmeter

Frequency Counter

600 ohm Feedthrough Termination, ±1%

Procedure :

1. Connect the equipment as shown below

Model

TEK FG504T, or equivalent

Fluke 8506A, or equivalent

HP 5316A, or equivalent

TEK 011-0092-00, or equivalent

Fig. 10.2.6.3.1. Test setup for measuring the line frequency

rejection.

2. Set the controls on the AC voltmeter as follows:

Function AC VOLTS

Mode HIGH ACCURACY

Range AUTO

B-22
3. Set the frequency of the audio oscillator to 60 Hz as indicated by the

frequency counter. Adjust the amplitude of the audio oscillator such that the

voltmeter indicates nominally 1.0 V ac (rms). Read and record on the data

sheet the actual voltage level.

4. Set the controls on the UUT as follows:

Filters (all) OFF

Ratio OFF

5. If provided, select the dB RATIO on the UUT and depress the PUSH TO SET 0

dB REF and set the LIN/LOG mode to LOG mode.

6. Select the High Pass Filter on the UUT.

7. Read and record on the data sheet the display indicated on the UUT. If

the UUT is capable of displaying voltage levels in dB, record the value

indicated. If the UUT is not capable of displaying the voltage level in dB,

calculate and record the rejection of the High Pass Filter at 60 Hz, in dB,

using:

Rejection (dB) = 20 log (Indicated Voltage / Input Voltage)

Where: the Input Voltage is that voltage indicated on the voltmeter

(step 3), and

the Indicated Voltage is that voltage read on the UUT (steo 7).

3-23
10.2.7 MODE SELECTION

Specification:

The front panel shall include controls to select mode of operation

(distortion, SINAD or voltmeter).

Procedure :

1. Assure that the front panel includes controls to select the mode of

operation (distortion, SINAD or voltmeter). Note on data sheet if this

condition is met.

B-24
10.2.8 COMMON MODE REJECTION RATIO (CMRR)

Specification:

For a common mode signal of < 1 volt rms, the common mode rejection ratio in

the frequency range from 50 ITz to 800 Hz, shall be greater than 40 dB.

Equipment

:

Items

Audio Oscillator

AC Calibrator

Spectrum Analyzer

Coupling Transformer

Procedure:

Range

5 kHz

50 Hz-800 Hz

50 Hz-5 kHz

5 kHz

Model

HP204D or equivalent

Fluke 5200A or equivalent

HP3585A or equivalent

UTC-LS-34 or equivalent

1. Connect the equipment as shown below.

Coupling

transformer

Fig. 10.2.8. Test setup for measuring tne common mode rejection

ratio.

2. Set the controls of the UUT as follows:

Function

Range

Filters (all)

AC VOLTS LEVEL

AUTO RANGE

OFF

B-25
3. Set the controls of the audio oscillator as follows:

Frequency

Output Level

NOMINAL 5 kHz

NOMINAL 100 mv *

* Note: The unit under test can be used as the indicator for the audio

oscillator nominal output level.

4. Set the controls of the AC calibrator as follows:

6. Record the reading on the UUT as V6.

7. Measure the peak amplitude of the 5 kHz signal on the spectrum analyzer

and record as Vy.

8. Measure the peak amplitude of the 50 Hz signal on the spectrum analyzer

and record as Vg.

9. Change the frequency of the AC calibrator to 800 Hz.

10. Measure the peak amplitude of the 800 Hz signal on the spectrum analyzer

and record as Vg.

11. Calculate the common mode rejection ratio for the 100 mv range as follows:

CMRR at 50 Hz = 20 Log “

Frequency

Voltage

50 Hz

1 VOLT

5. Set the controls of the spectrum analyzer as follows:

Ampl itude

Sweep Rate

Sweep start

Sweep stop

Displ ay

0 Hz

AS NEEDED

VOLTS

AUTORANGE

TWO STEPS SLOWER THAN AUTOMATIC

CMRR at 800 Hz = 20 Log Vy

(V6)(Vg)

B-26
10.2.9 OVERLOAD PROTECTION

Specification:

The instrument shall be protected to at least a rms value of 175 volts and

shall be capable of performing to all specf ications after being subjected to

an overload voltage up to 175 volts rms.

Equipment ;

ITEM RANGE MODEL

AC Calibrator FluKe 5200A or equivalent

Power Amplifier 175 V Fluke 5205A or equivalent

Procedure :

1. Connect the equipment as shown below. NOTE: Extreme caution must be used

when the power amplifier is operational.

Line cord

Fig. 10.2.9. Test setup for measuring overload protection.

2. Set the controls on the UUT as follows:

Range AUTORANGE

Function AC VOLTS

B-27
3.

Set the controls on the AC calibrator as follows:

Amplitude 175 V

Frequency 60 Hz

4. Maintain a 175 volt rms, 60 Hz level to the input of the UUT for 2

minutes.

5. Deenergize the calibrator and perform all test procedures for

specification conformance.

B-28
10.2.10 RELATIVE dB REFERENCE

Specification

:

The equipment shall be capable of setting a measurement made in dB and dBm as

a zero reference. The control to set the dB reference shall be located on the

front panel

.

Procedure :

Assure that the UUT has a control on the front panel to set a zero dB

reference level. Note and record on the data sheet whether or not this

condition is met.

B-29
10.2.11 BANDWIDTH

Specification ;

The 3dB bandwith of the equipment shall be at least 300 kHz.

Equipment :

ITEMS RANGE MODEL

AC Calibrator 100 MV to 10 V Fluke 5200A or equivalent

Power Amplifier 10 V to 130 V Fluke 5205A or equivalent

Procedure :

1. Connect the equipment as shown below

AC

calibrator

‘ UUT

f input

Fig. 10.2.11A Test setup for measuring the bandwidth (upper cutoff

frequency) of the UUT for input levels up to 100

volts rms.

2. Set the controls of the unit under test as follows:

Filters (all) OFF

Function AC VOLTS

Ratio dB

Range AUTORANGE

B-30
3. Set the controls of the AC calibrator as follows:

Voltage 100 mV

Frequency 1 kHz

4. Set the zero dB reference button,

5. Change the frequency of the AC calibrator to 300 kHz.

6. Note and record the display indication on the UUT.

7. Repeat steps 3 thru 6 for AC calibrator levels of 1 V and 10 V.

8. Reconnect the equipment as shown below. NOTE: Extreme caution must be

used when the power amplifier is operational.

Line cord

Fig. 10.2.11B Test setup for measuring the bandwidth (upper cutoff

frequency) of the UUT for input levels above

100 volts rms.

9.

Repeat steps 3 thru 6 for an output level of 130 V rms from the power

amplifier.

B-31
10.2.12 INPUT IMPEDANCE

Specification:

The input impedance in the distortion mode shall be 100 accurate to within

±2^ shunted by less than 300 picofarads.

Equipment :

ITEMS RANGE MODEL

Digital LCR meter

Isolation Transformer

Three-wire-female to two-wire-male adapter

HP4262A or equivalent

Topaz 91002-22 or equivalent

Order by description

Procedure:

1. Connect the equipment as shown below

Fig. 10.2.12. Test setup for measuring input impedance.

Note: This procedure requires that the chassis of the UUT be ungrounded with

respect to earth ground. Assure that adequate safety precautions are observed.

B-32
2.

Set the controls on the UUT as follows:

Function

Range

DISTORTION MEASUREMENT

AUTORANGE

3.

Set the controls on the LCR meter as follows:

Circuit Mode

Function

Test Signal

DC Bias OFF

PRL

C

LCR Range

DQ Range

Trigger

1 kHz

AUTO

AUTO

INT

4. Disconnect the BNC cable to the input of the UUT.

5. Read and record on the data sheet the value of the cable capacitance as indicated by the LCR meter.

6. Reconnect the BNC cable to the input of the UUT.

7. Read and record on the data sheet the value of the sum of the cable and

input capacitance indicated in the LCR display.

8. Subtract the value of the capacitance obtained in step 5 from the value of » the capacitance obtained in step 7. Record this difference on tne data sheet.

9. Press ‘the R/ESR button on the LCR meter.

10. Read and record on the data sheet the value of the input resistance

indicated on the LCR display.

B-33
10.2.13 FUNDAMENTAL FREQUENCY LOCKING

Specification;

There shall be an indication on the front panel as to when the distortion

analyzer is locked on the fundamental component of the input signal.

Procedure :

Assure that the UUT is provided with a front panel indication as to when the

UUT is locked on the fundamental. If the UUT does not have a dedicated

indicator of frequency locking but uses some other indirect front panel

indication such as a display of frequency this can be observed and noted in

the DISTORTION MEASUREMENT ACCURACY (10.3.4) test procedure. Note and record

whether this condition exists.

B-34
10.3.1 FUNDAMENTAL FREQUENCY RANGE

Specification:

The equipment shall cover the fundamental frequency range from 20.0 Hz to

100.0 kHz.

Equipment :

Manufacturer's manual for UUT.

Procedure :

Read the manual for the UUT and note whether the specifications indicate a fundamental frequency range from 20.0 Hz to 100 kHz. Note and record on the

data sheet whether the above range is indicated. Note: The distortion and

SINAD test procedures exercise the UUT over the 20.0 Hz to 100 kHz range.

B-35
10.3.2 INPUT LEVEL RANGE

Specifications:

The minimum input level range for distortion and SINAD measurements shall be

from 100.0 millivolts rms to 130.0 volts rms.

Equipment :

Manufacturer's manual for UUT.

Procedure :

Read the manual for the UUT and note whether the specifications indicate an input level range of 100.0 millivolts rms to 130 volts rms for distortion and

SINAD measurements. Note and record on the data sheet whether the UUT is

specified to operate within the above levels. Note: The distortion and SINAD

test prcedures exercise the UUT over the 100.0 millivolt to 130 volt range.

B-36
10.3.3 DISTORTION MEASUREMENT RANGE

Specification

The equipment's distortion measurement range shall cover, within specified

accuracy, the range from 0.1% (-60 dB) to 50% (-6dB).

Procedure :

The test procedure for the above (10.3.3) specification is included in part ofc

the test procedure outlined for 10.3.4 by measuring the accuracy over the

range from -60 dB to -6 dB.

B-37
10.3.4 DISTORTION MEASUREMENT ACCURACY

Specification ;

The accuracy of the distortion measurement across the full bandwidth and

voltage range shall be within the following:

Fundamental Frequency Range Accuracy

20 Hz - 20 kHz ±1 dB

20 kHz - 50 kHz ^2 dB

50 kHz - 100 kHz ±3 dB, -4 dB

10.3.4 Part 1. Distortion Measurement with Two Sine Waves

Equipment:

ITEM RANGE MODEL

Low-Distortion Oscillator 20 Hz to 100

Audio Oscillator 40 Hz to 300

AC Voltmeter 20 Hz to 300

600 Resistor (2)

Power Amplifier

Spectrum Analyzer

kHz Tektronix SG5010 or equivalent

kHz HP204D or equivalent

kHz Fluke 8506A or equivalent

see appendix F Fluke 5205A or equivalent

HP3585A or equivalent

Procedure :

1. Connect the equipment to the UUT as shown below

Fig. 10.3.4A Test setup for measuring distortion accuracy with sine wave signals. Note, the 600 series resistors may be

omitted if the oscillators have an output impedance of

600 ohms or greater.

B-38
2.

Set the controls of the UUT as follows:

Range

Function

Display mode

Filters (all)

Detection mode

AUTORANGE MODE

DISTORTION

dB (log)

OFF

RMS

3.

Set the controls of the voltmeter as follows:

Function

Mode

Range

AC VOLTS

HIGH ACCURACY

AUTO

4. Refer to the data sheet table 10.3.4A for setting the frequencies,

amplitude, and attenuation levels of the oscillators. Repeat steps 5 through

11 inclusive for each line of data.

5. Set the frequency of the low-distortion oscillator and audio oscillator to

the indicated frequencies.

6. Set the output level of the audio oscillator to a minimum.

7. Set the output level of the low-distortion oscillator so that the

voltmeter reads the nominal amplitude level given in the table. Note the

level setting on the low-distortion oscillator and record the actual reading

on the A6 voltmeter.

8. Set the low-distortion oscillator to a minimum output level and adjust the

audio oscillator to give the same voltmeter reading obtained in step 7.

9. Change the attenuator setting on the audio oscillator to attenuate to the

ac voltmeter level recorded in the table.

10. Reset the low-distortion oscillator to the same level noted in step 7.

11. Read and record the display of the UUT.

The following four steps (12 through 15) are intended to test the RESPONSE

TIME (10.2.5).

12. Repeat the measurement of the second line of table 10.3.4A (i.e. 20 Hz,

O.IV, 40 Hz, 60 dB) and note the distortion value indicatea by the UUT.

13. Remove the signal cable from the input of the UUT.

14. Reconnect the signal cable and time the UUT to display the level noted in

step 12.

15. Record the time on data sheet 10.2.5.

5-39
The following 4 steps (16 through 18) are intended to test the FUNDAMENTAL

REJECTION 16. (10.3.7).

Connect the spectrum analyzer to the UUT monitor output and switch the

function of the UUT to DISTORTION.

17.

Set the controls of the spectrum analyzer as follows:

Sweep Start

Sweep Stop

Displ ay

Ampl itude

Sweep Rate

0 Hz

AS NEEDED

LOG 10 dB/DIV

AUTORANGE

TWO STEPS SLOWER THAN AUTOMATIC

18. Refer to the data sheet table 10.3.7 for setting the frequencies,

amplitude, and attenuation levels of the oscillators. Repeat steps 5 through

10 inclusive and record the peak amplitude in dB of the two frequencies

indicated on the spectrum analyzer for each line of data.

19. Set the function of the UUT back to DISTORTION.

20.

Reconnect the equipment to the UUT using the power amplifier as shown

below. NOTE, extreme caution must be used when the power amplifier is

operational

.

Fig. 10.3.4B. Test setup for measuring distortion accuracy with sine wave sianals above 10 volts. Note, the 600 n series

resistors may be omitted if the oscillators have an output impedance of 600 ohms or greater.

21.

Refer to the data sheet table 10.3.4B for setting frequencies, amplitude,

and attenuation levels of the oscillators. Repeat steps 5 through 11

inclusive for each line of data. „
10.3.4 Part 2. Distortion Measurment with a 3:1 Crest Factor Signal

Equipment:

ITEM

Arbitrary Waveform Generator

SpectriffTi Analyzer

488 Controller

3:1 Crest Factor program

Low Pass Filter

100: 1 Attenuator Probe

Power Amplifier

Procedure:

RANGE MODEL

20 Hz to 300 kHz

20 Hz to 300 kHz

20 Hz to 300 kHz

3 dB at 200 kHz

10 V to 130 V

Wavetek 275 or equivalent

HP3585A or equivalent

Hp9836 or equivalent

ARB- 15, see appendix D see appendix E Tektronix P6007 or equiv

Fluke 5205A or equiv.

1. Connect the equipment to the UUT as shown below:

Fig. 10.3.4C. Test setup for measuring distortion accuracy with

signals that have a 3:1 crest factor.

B-41
2. Set the controls of the UUT as follows:

Range

Function

Display Mode

Filters (all)

Detection Mode

AUTORANGE

DISTORTION

dB (log)

OFF

RMS

3. Set the controls of the spectrum analyzer as follows:

Sweep Start

Sweep Stop

Displ ay

Ampl itide

Level Indication

Sweep Rate

Input Connection

0 Hz

AS NEEDED

5 dB/DIV

AUTORANGE

VOLTS

TWO STEPS LONGER THAN AUTOMATIC

1 M ohm INPUT

4. Load the program, ARB-15 into the 488 controller and run the program.

5. Refer to the data sheet table 10.3.4C for setting the frequencies and

amplitudes of the generator. Repeat steps 6 through 11 inclusive for each

frequency and amplitude indicated.

6. Set the frequency of the arbitrary waveform generator to the indicated

frequency.

7. Using the spectrum analyzer readings adjust the amplitude of the arbitrary

waveform generator to give the nominal desired fundamental amplitude within 10

percent.

8. Read and record the actual fundamental amplitude.

9. Read and record all the harmonics with amplitudes greater than Tk of the

fundamental amplitude.

10. Calculate the root sum square (rss) of the harmonic amplitudes recorded

in step 9.

11. Record the distortion indicated on the UUT.

B-42
12. Reconnect the equipment to the UUT as shown below. Note: Use extreme

caution when the power amplifier is operational.

Fig, 10.3.4D. Test setup for measuring distortion accuracy of

signals with a 3:1 crest factor and peak

amplitudes above 10 volts,

13. Refer to the data sheet table 10.3.4D for setting the frequency and

amplitude of the generator. Repeat steps 6 through 11 inclusive for each line

of data.

B-43
10.3.6 SI NAD MEASUREMENT ACCURACY

Specification:

The accuracy of the SINAD measurement

specified in para. 10.3.4.

Fundamental Frequency Range

20 Hz - 20 kHz

30 kHz - 50 kHz

50 kHz - 100 kHz

shall be within the same accuracy as

Accuracy

±1 dB

±2 dB

±3 dB, -4 dB

Equipment :

ITEMS RANGE MODEL

Low-Distortion Oscillator

Noise Generator

AC Voltmeter

600 Resistor (2)

Low Pass Filter

Power Anplifier

20 Hz to 100 kHz

20 Hz to 300 kHz

20 Hz to 300 kHz

3 dB at 200 kHz

10 V to 130 V

Tektronix SG5010 or equivalent

Wavetek 132 or equivalent

Fluke 8506A or equivalent

see appendix F see appendix E Fluke 5205A or equivalent

Procedure :

1. Connect the equipment to the UUT as shown below

Fig. 10.3.6A. Test setup for measuring SINAD accuracy. Note, the

600 ^series resistors may be omitted if the oscillators

have an output impedance of 600 ohms or greater.

B-44
2.

Set the controls of the UUT as follows:

Range

Function

Display mode

Filters (all)

Detection mode

AUTORANGE MODE

SI NAD

dB (log)

OFF

AVERAGE

3.

Set the controls of the voltmeter as follows:

Function

Mode

Range

AC VOLTS

HIGH ACCURACY

AUTO

4. Refer to the data sheet table 10.3.6A for setting the amplitude of the

noise generator, the frequency of the low-distortion oscillator, and the

combined amplitude of both generators. Repeat steps 5 through 9 inclusive for

each line of data.

5. Set the frequency of the low-distortion oscillator as indicated.

6. Set the output of the low-distortion oscillator to a minimum.

7. Set the output level of the noise generator to the level indicated in the

table. Use the voltmeter to establish the required level.

8. Increase the output amplitude of the low-distortion oscillator to. obtain

the combined amplitude indicated in the table. Again use the voltmeter to

establish the required level.

9. Read and record the SINAD indication on the UUT.

B-45
10. Reconnect the UUT as shown below, NOTE: Extreme caution must be used

when the power amplifier is operational.

Note

Fig. 10.3.6B. Test setup for measuring SINAD accuracy with signals

above 10 volts. Note, the 600 .F’ series resistors may

be omitted if the oscillators have an output impedance

of 600 ohms or greater.

11. Refer to the data sheet table 10.3.6B for setting the amplitude of the

noise generator, the frequency of the low-distortion oscillator, and the

combined amplitude of both generators. Repeat steps 5 through 9 inclusive for

each line of data.

B-46
10.3.7 FUNDAMENTAL REJECTION

Specification :

The distortion analyzer shall reject the fundamental component of the input

signal by at least 10 dB below the total harmonic distortion and noise level.

Procedure :

The test procedure for this specification is contained* in the test procedure

for DISTORTION MEASUREMENT ACCURACY (10.3.4) steps 16 through 18.

B-47
10.3.8 MEASUREMENT MODE

Specification:

The equipment shall display distortion in dB and percent and SINAD in dB.

Measurement mode shall be selectable by front panel control.

Procedure :

1. Assure that the UUT displays distortion in dB and percent and that the

measurement mode is selectable by a front panel control. Note on the data

sheet if this condition is met.

B-48
10.3.9 RESIDUAL DISTORTION AND NOISE

Specification:

Without using any filters, for both rms and average response, the total

distortion + noise introduced by the equipment across the entire voltage range

shall be less than -65 dB (.056%) across the entire bandwidth of the

equipment.

Equipment

:

ITEM RANGE MODEL

Low-Distortion Oscillator

AC Voltmeter

Low Pass Filter

20 Hz to 100 kHz

100 mV to 130 V 3 dB at 200 kHz

Tektronix SG5010 or equivalent

Fluke 8506A or equivalent

see appendix E

Procedure:

1. Connect the equipment as shown below

Fig. 10.3.9A. Test setup for measuring residual distortion and noise.

B-49
2.

Set the UUT controls as follows:

ON/OFF Switch

Function

Display Mode

Filters (all)

Range Mode

ON

DISTORTION

dB (log)

OFF

AUTORANGE

3.

Refer to the data sheet table 10.3.9A for setting the frequency and

amplitude of the low-distortion oscillator. Repeat steps 4 and 5 inclusive

for each line of data.

4.

Set the frequency and amplitude of the low-distortion oscillator to the

indicated values.

5.

Read and record the value displayed on the UUT.

6.

Reconnect the equipment as shown below. NOTE: Use extreme caution when

the power amplifier is operational.

Fig. 10.3.9B. Test setup for measuring residual distortion and noise

at input levels above 10 volts.

7. Refer to the data sheet table 10.3.9B for setting the amplitude and

frequency to the UUT.

8. Repeat steps 4 and 5 inclusive for each line of data.

B-50
10.3.10 LEVEL UNDERRANGE/OVERRANGE INDICATION

Specification :

There shall be on the panel an indication to indicate when the input signal is

not within the accuracies as specified in para 10.3.4.

Procedure :

Assure that there is a digital indication on the front panel to indicate when

the input signal is not within the range to maintain the accuracies specified

in para 10.3.4. Note on the data sheet if this condition is met.

B-51
10.4.1 VOLTAGE RANGE

Specification:

The minimum range of the AC voltmeter shall be from 100 millivolts true rms to

130 volts true rms.

Equipment :

Manufacturer's manual for OUT.

Procedure :

Read the manuals for the OUT and note whether the AC voltmeter range covers

the limits specified and whether the measurement method is based on true rms type detection.

B-52
10.4.2 VOLTMETER ACCURACY

Specification:

The AC voltmeter shall be accurate over the entire range as specified in para.

10.4.1, to within ±2% of the reading in the fundamental frequency range of

20* Hz to 20 kHz, and ±4% in the fundamental frequency range from 20 kHz to 100

kHz.

Equipment :

items RANGE MODEL

AC Calibrator 1 mV to 100 V AC (rms) Fluke 5200A or equivalent

Procedure :

1. Connect the equipment as shown below

Fig. 10.4.2. Test setup for measuring voltmeter accuracy.

Warning: High voltages are employed in this test procedure. Assure that aii

equipment is properly grounded and that all applicable safety

procedures are followed.

B-53
2. Set the controls on the UUT as follows:

3.

4.

5.

6 .

7.

8 .

9.

10 .

11 .

12 .

13.

14.

15.

16.

17.

18.

19.

20 .

21 .

22 .

23.

24.

25.

26.

Function

Filters (all)

Range

AC VOLTMETER MODE

OFF

AUTO

Set the frequency of the meter calibrator to 20 Hz.

Set the voltage output of the meter calibrator to 0.100 V AC (rms).

Read and record on the data sheet the voltage measured by the UUT.

Set the voltage output of the meter calibrator to 1.000 V AC (rms).

Read and record on the data sheet the voltage measured by the UUT.

Set the voltage output of the meter calibrator to 10.00 V AC (rms).

Read and record on the data sheet the voltage measured by the UUT.

Set the voltage output of the meter calibrator to 100.0 V AC (rms).

Read and record on the data sheet the voltage measured by the UUT.

Set the frequency of the meter calibrator to 60 Hz.

Repeat steps 4 through 11, inclusive.

Set the frequency of the meter calibrator to 400 Hz.

Repeat steps 4 through 11, inclusive.

Set the frequency of the meter calibrator to 1000 Hz.

Repeat steps 4 through 11, inclusive.

Set the frequency of the meter calibrator to 5 kHz.

Repeat steps 4 through 11, inclusive.

Set the frequency of the meter calibrator to 10 kHz.

Repeat steps 4 through 11, inclusive.

Set the frequency of the meter calibrator to 20 kHz.

Repeat steps 4 through 11, inclusive.

Set the frequency of the meter calibrator to 50 kHz.

Repeat steps 4 through 11, inclusive.

Set the frequency of the meter calibrator to 100 kHz.

B-54
27. Repeat steps 4 through 11 inclusive.

28. Repeat the measurement in step 4 and note the level on the UUT display.

29. Change the calibrator to 100 volts.

30. Change the calibrator back to 0.1 volts and measure the time for the

display to settle to the value noted in step 28.

31. Record the response time on data sheet 10.2.5.

32. Set the voltage output of the calibrator to zero, turn off, and

disconnect the equipment.

B-55
10.4.3 MEASUREMENT MODE

Specification:

The equipment shall display level in rms volts, millivolts and dBm (into 600

ohms). Measurement mode shall be selectable by front panel control.

Procedure :

1. Assure that the UUT displays level in rms volts and dBm (into 600 ohms)

and that the measurement mode is selectable by a front panel control. Note on the data sheet if this condition is met.

B-56
10.4.4 LEVEL OVERRANGE INDICATION

Specification:

There shall be on the front panel an indication to indicate when the input

signal is not within the accuracies as specified in para. 10.4.2.

Procedure :

Assure that there is a digital indication on the front panel to indicate when

the input signal is not within the range to maintain the accuracies as specified in para. 10.4.2. Note on the data sheet if this condition is met.

B-57

APPENDIX C

SPECIFICATION PERFORMANCE

DATA SHEETS AND TABLES

FOR USE WITH TEST PROCEDURES

IN APPENDIX B

C-1
Specification Performance

Data Sheet

Bid Sample ID No.

Reference Specification Measurement Data, Acceptab" e Limits Units

Paragraph Description Observations, Notes, etc. Min. Max

.

10.1 Operation

10.1.1 Distortion

Measurement

10.2.1 Displ ay

10.2.1.1 Displ ay 0.1 dB, %

Resolution 100 counts

10.2.2 Input

Connector

•

10.2.3 Monitor Output Use Tables

Connector 10.2. 3A

and

10.2.3B

10.2.3.1 Output

Impedance

5) Voltage VI -- Volts

7) Voltage V2

9) Cal . Output

• “ *• — Volts

Impedance 570 630 Ohms

C-2
Specification Performance

Data Sheet

Bid Sample ID No.

Reference

Paragraph

Specification

Description

Measurement Data,

Observations, Notes, etc.

Acceptab' e Limits Units

Min. Max.

10.2.4 Detection

10.2.5 Response

Time

[Performed in steps 28-

30 of 10.4.2 and steps

12-15 of 10.3,4]

10 Seconds

10.2.6 Filters 3 Fi Iters

10.2.6.1 Low-Pass

Filter

3) Voltmeter

Reading

8) -3 dB Freq.

11) Rolloff

28 32

-60

Volts

kHz

dB

10.2.6.2 Low-Pass

Filter

3) Voltmeter

Reading

8) -3 dB Freq.

11) Rolloff

76 84

-60

Volts

kHz

dB

C-3
Specification Performance

Data Sheet

Bid Sample ID No.

Reference Specification Measurement Data, Accept ab' e Limits Units

Paragraph Description Observations, Notes, etc. Min

.

Max

.

10.2.6.3 High-Pass

Filter

3) Voltmeter

Reading Vol ts

8) -3 dB Freq. 360 440 Hz

11) rolloff -60 dB

10.2.6.3.1 Line Freq.

Rejection

3) Voltmeter

Reading Volts

7) Rolloff • -40 dB

10.2.7 Mode

Selection

10.2.8 Common -Mode

Rejection

Ratio

6) Voltage V6 — -- Volts

7) Voltage V7 -- -- Volts

8) Voltage V8 -- -- Volts

9) Voltage V9

10) Calc. CMRR

Volts

0 50 Hz 40 — dB

10) Calc. CMRR

0 800 Hz 40 dB

C-4
Specification Performance

Data Sheet

Bid Sample ID No.

Reference Specification Measurement Data, Acceptab' e Limits Units

Paragraph . Description Observations, Notes, etc. Min. Max

.

10.2.9 Overload

Protection 175 V rms

10.2.10 Rel ative

dB Reference

10.2.11 Bandwidth

6) 100 mV -3 dB

7) 1 V -3 dB

7) 10 V -3 dB

9) 100 V

0 -3 dB

10.2.12 Input

Impedance

5) Cable Cap

7) Cable + — — pF

Input Cap — — pF

8) Input Cap — — pF

10) Resistance 98k 102k Ohms

10.2.13 Fundamental 1 Frequency 1

1 Locking 1

!

10.3.1 Fundamental

Frequency

Range 20 100k Hertz

C-5
Specification Performance

Data Sheet

Sid Sample ID No.

Reference Specification Measurement Data, Accept abl e Limits Units

Paragraph Description Observations, Notes, etc. Min. Max.

10.3.2 Input Level

Range 0.1 130 volts

10.3.3 Di stortion

Measurement 0.1 50 %

Range -60 -6 dB

10.3.4 Distortion Use Tables

Measurement 10.3.4A, 10.3.4B,

Accuracy 10.3.4C, 10.3.4D

10.3.6 SINAD

Measurement Use Tables

Accuracy 10.3.6A, 10. 3. 68

10.3.7 Fundamental Use Table

Rejection 10.3.7

10.3.8 Measurement

Mode

10.3.9 Residual Use Tables

Distortion & 10.3.9A, and

Noise 10. 3. 98

10.3.10 Level

Under/Over

Range Indie.

10.4.1 Voltage

Range

C-6
Specification Performance

Data Sheet

Bid Sample ID No.

Reference

Paragraph

Specification

Description

Measurement Data,

Observations, Notes, etc.

Acceptab' e Limits Units

Min. Max

.

10.4.2 Voltmeter

Accuracy

Frequency=20 Hz

5) 0.100 V ac 0.09800 0.10200 Volts

7) 1.000 V ac 0.98000 1.02000 Volts

9) 10.00 V ac 9.80000 10.2000 Volts

11) 100.0 V ac 98.0000 102.000 Volts

Frequency=60 Hz

5) 0.100 V ac 0.09800 0.10200 Volts

7) 1.000 V ac 0.98000 1.02000 Volts

9) 10.00 V ac 9.80000 10.2000 Volts

11) 100.0 V ac 98.0000 102.000 Volts

Frequency=400Hz

5) 0.100 V 0.09800 0.10200 Volts

7) 1.000 V 0.98000 1.02000 Volts

9) 10.00 V 9.80000 10.2000 Volts

11) 100.0 V 98.0000 102.000 Volts

Frequency=lkHz

5) 0.100 V 0.09800 0.10200 Volts

7) 1.000 V 0.98000 1.02000 Volts

9) 10.00 V 9.8000 10.2000 Volts

11) 100.0 V 98.0000 102.000 Volts

i

C-7
Specification Performance

Data Sheet

Bid Sample ID No.

Reference

Paragraph

Specification

Description

Measurement Data,

Observations, Notes, etc.

Acceptab' e Limits Units

Min. Max

.

10.4.2 Voltmeter

Cont

.

Accuracy

Frequency=5 kHz

5) 0.100 V ac 0.09800 0.10200 Volts

7) 1.000 V ac 0.98000 1.02000 Volts

9) 10.00 V ac 9.80000 10.2000 Volts

11) 100.0 V ac 98.0000 102.000 Volts

Frequency=10kHz

5) 0.100 V ac 0.09800 0.10200 Volts

7) 1.000 V ac 0.98000 1.02000 Volts

9) 10.00 V ac 9.80000 10.2000 Volts

11) 100.0 V ac 98.0000 102.000 Volts

Frequency=20kHz

5) 0.100 V ac 0.09800 0.10200 Volts

7) 1.000 V ac 0.98000 1.02000 Volts

9) 10.00 V ac 9.80000 10.2000 Vol ts

11) 100.0 V ac 98.0000 102.000 Volts

Frequency=50kHz

5) 0.100 V ac 0.09600 0.10400 Volts

7) 1.000 V ac 0.96000 1.04000 Volts

9) 10.00 V ac 9.60000 10.4000 Volts

11) 100.0 V ac 96.0000 104.000 Volts

Freq. = 100 kHz

5) 0.100 V ac 0.09600 0.10400 Volts

7) 1.000 V ac 0.96000 1.04000 Volts

9) 10.00 V ac 9.60000 10.4000 Volts

11) 100.0 V ac 96.0000 104.000 Volts

C-8
Specification Performance

Data Sheet

Bid Sample ID No.

Reference

Paragraph

Specification

Description

Measurement Data,

Observations, Notes, etc.

Acceptab^ e Limits Units

Min. Max.

10.4.3 Measurement

Mode

10.4.4 Level

Overange

Indication
Table 10. 2. 3. A. Monitor Output Connector, Part 1 (Sine Wave Signals)

AC Ca‘ i brat or AC Voltmeter Normalized Acceptable Limits

Freq. Ampl

.

Indication Indication Devi at ion Level

Hz V V % % Min V Max V

20 0.1 1 .05 5

Ik 0.1 Ref=0 Ref=0 .05 5

100k r—

1

o • + 10 .05 5

20 1 + 10 .05 5

Ik 1 Ref=0 Ref=0 .05 5

100k 1 + 10 .05 5

20 10 1 10 .05 5

Ik 10 Ref=0 Ref=0 .05 5

100k 10 1 10 .05 5

20 100 1 10 .05 5

Ik 100 Ref=0 Ref=0 .05 5

look 100

• 1 10 .05 5

20 130 + 10 .05 5

Ik 130 Ref=0 Ref=0 .05 5

100k 130 + 10 .05 5

C-10
Table 10.2.3.B. Monitor Output Connector, Part 2 (3:1 Crest Factor Signals)

Arbitrary Waveform Gen Monitor Output

Freq. Ampl

.

Cl ipping

Hz V No Yes

20 0.1

1

10

100

130

20k 0.1 •

1 ---- —

10

100

130

C-11
Table 10.3.4A. Distortion Measurement Accuracy, Part 1 (Sine Wave Signals up to lOV rms)

Low-Distortion Oscillator Audio Oscillator OUT Indication Accept. Limits

Freq. Norn . /Vnp 1

.

Meas. 4mpl

.

Freq. Attn. Distortion Min. Max,

Hz V V . Hz dB dB dB dB

20 0.1 40 10 9 11

60 59 61

1 10 9 11

60 59 61

10 10 9 11

200 0.1 600 10 9 11

60 59 61

1 10 9 11

60 59 61

10 10 9 'll

60 ———————————— • 59 61

2k 0.1 4k 10 9 11

20 19 21

30 29 31

40 39 41

50 49 51

60 59 61

1 10 9 11

60 59 61

6k 10 9 11

20 19 21

30 29 31

C-12
Table 10.3.4A. Distortion Measurement Accurcy, Part 1 (Continued)

C-13
Table 10.3.4A. Distortion Measurement Accuracy, Part 1 (Continued)

Low--Distortion Oscillator Audio Oscillator UUT Indication Accept. Limits

Freq. Norn. Ampl

.

Meas. Ampl. Freq. Attn. Distortion Min. Max.

Hz V V Hz dB dB dB dB

100k 0.1 200k 10 6 13

60 56 63

300k 10 6 13

60 56 63

1 300k 10 6 13

60 56 63

200k 10 6 13

60 56 63

10 200k 10 . 6 13

60 56 63

300k 10 58 13

60 6 63

56 13

C-14
Table 10.3.4B. Distortion Measurement Accuracy, Part 1 (Sine Wave Signals Above 10 V rms)

Low Distortion Oscillator Audio Osci 1 1 ator UUT Indication Accep. Limits

Freq. Norn. Ampl . Meas. /Vnpl

.

Hz Volts Volts

Freq.

Hz

Attn

.

dB

Di stortion

dB

Min.

dB

Max

.

dB

20 100 40 10 - - - - 9 11

60 - - - - 59 61

200 100 600 10 - - - - 9 11

60 - - - - 59 61

2k 100 4k 10 - - - - 9 11

60 - _ _ - 59 61

6k 10 - - - - 9 11

60 - - - - 59 . 61

• 20k 100 —

40k 10 - - - - 8 12

60 - - - - 58 62

60k 10 - - - - 3 12

60 - - - - 58 62

100k 100 200k 10 - - - - 6 13

60 - - - - 56 63

300k 10 - - - - 6 13

60 56 63

C-15
Table 10.3.4C Distortion Measurement Accuracy, Part 2 (3 to 1 Crest Factor Signals Up to 1 volt)

Arbitrary Waveform Gen

Norn. Freq,

Hz

20

20

Fund. Ampl

V

0.1

Meas. Ampl

V

Ampl. of Harmonics

> 2% of Fund.

RSS

Di St.

dB

UUT

Indie

dB

Acceptable

Difference

dB

±1

±1

C-16
Table 10.3.4C. Distortion Measurement Accuracy, Part 2

(Continued)

Arbitrary Waveform Gen

Notn. Freq.

Hz

200

200

Fund. Ampl

V

0.1

Meas. Ampl

V

Ampl. of Harmonics

> 2% of Fund.

RSS

Dist

dB

UUT

Indie

dB

Acceptable

Difference

dB

±1

C-17
Table 10.3.4C Distortion Measurement Accuracy, Part 2 (Continued)

Arbitrary Waveform Gen

Norn. Freq.

Hz

2k

2k

Fund. Ampl

V

0.1

Meas. Ampl

V

Ampl. of Harmonics

> 2% of Fund.

RSS

Dist.

dB

UUT

Indie

dB

Accept able_

Difference'

dB

±1

xl

C-18
Table 10.3.4D Distortion Measurement Accuracy, Part 2 (3 to 1 Crest Factor Signals above 1 volt)

Arbitrary Waveform Gen Ampl. of Harmonics RSS UUT Acceptable

> 2% of Fund. Di St. Indie. Difference

Norn. Freq. Fund . AmplMeas. Ampl.

Hz V V V dB dB dB

20 10

*

1

n

20 100

•

1

j

zl

C-19
Table 10.3.4D Distortion Measurement Accuracy, Part 2

(Continued)

Arbitrary Waveform Gen

Norn. Freq,

Hz

200

200

Fund. Amp!

V

10

100

Meas. Ampl

V

Ampl. of Harmonics

> 2% of Fund.

V

RSS

Dist

dB

UUT

Indie.

Acceptablj

Differencj

dB dB

±1

±1

C-20
Table 10.3.4D Distortion Measurement Accuracy, Part 2

(Continued)

Arbitrary Waveform Gen Ampl . of Harmonics

> 2% of Fund

RSS

Di St.

UUT Acceptable

Indie. Difference

Freq. Norn, Hz

2k

Fund. Ampl

V

10

Meas. Ampl

V dB dB dB

2k 100

il

C-21
Table 10.3.6A SINAD Measurement Accuracy

(Combined Signal Amplitudes Up to 10 volts)

Noise Gen. Low-Dist. Oscil. Noise Gen. /Low-Dist. Oscil. UUT Acceptable Limits

Ampl

.

Freq. Combined Ampl. Indie. Min. Max.

V Hz V dB dB dB

0.01 20 0.316 — 29 31

1.00 — 39 41

3.16 — 49 51

10.0 — 59 61

0.1 20 0.316 — 9 11

1.00 — 19 21

3.16 — 29 31

10.0 — 39 41

1.0 20 3.16 — 9 11

10.0 — 19 21

0.01 200 0.1 — 19 21

3.16 — 49 51

0.1 200 1.0 — 19 21

10.0 — 39 41

1.0 200 3.16 — 9 11

10.0 — 19 21

0.01 2k 0.316 — 29 31

3.16 — 49 51

10.0 — 59 61

C-22
Table 10.3.6A SINAD Measurement Accuracy

(Continued)

Noise Gen. Low-Dist. Oscil. Noise Gen. /Low-Dist. Oscil. UUT Acceptable Limits

Anpl

.

FREQ. Combined Ampl

.

Indie

.

Min. Max

.

V Hz V dB dB dB

0.1 2k 0.316 9 11

1.0 — 19 21

10.0 — 39 41

1.0 2k 3.16 — 9 11

10.0 — 19 21

0.01 20k 10.0 — 58 62

0.1 20k 0.316 — 8 12

. 10.0 38 42

1.0 20k 3.16 — 8 12

10.0 — 18 22

0.01 100k 0.316 — 26

3.16 — 46 53

10.0 — 56 63

0.1 100k 0.316 — 6 13

3.16 — 26 33

10.0 — 36 43

1.0 100k 3.16 — 6 13

10.0 — 16 23

i

C-23
Table 10.3.6B SINAD Measurement Accuracy

(Combined Signal Amplitudes Above 10 volts)

Noise Gen. Low-Dist. Oscil. Noise Gen/Low-Dist. Oscil. OUT Acceptab' e Limits

Ampl

.

V Freq.

Hz

Combined Ampl.

V IndicationdB

Min.

dB

Max.

dB

0.1 20 100 — 59 61

0.1 200 100 — 59 61

0.1 2k 31.6 — 49 51

0.1 2k 100 — 54 61

1.0 2k 31.6 — 29 31

1.0 2k 100 — 39 41

0.1 20k 100 — 58 62

0.1 100k 100 — 56 63

1.0 100k 100 — 36 43

C-24
Table 10.3.7. Fundamental Rejection

Low Distortion Oscillator Aud i 0 Osci 1

.

Spectrum Analyzer Accept. Limit

Freq.

Hz

Non. Ampl.

V Meas. /^pl

.

V Freq.

Hz

Attn

.

dB

L-D Oscl

.

dB

Audio. Oscl

dB

Diff

.

dB

Min.

dB

20 0.1 «... 40 60 I..... 10

200 0.1 — 600 60 — — 10

2k 0.1 — 4k 60 — 10

20k 0.1 — 40k 60 — — 10

100k 0.1 200k 60 ---- — 10

C-25
Table 10.3.9A. Residual Distortion and Noise

(Up to 10 Volts)

Low-Distortion Oscillator UUT Indication Accept. Limits

Freq. Norn. Ampl

.

Di stortion Min.

Hz V dB dB

20 0.1 65

1 65

10 65

200 0.1 65

1 65

10 65

2k 0.1 65

1 65

10 65

20k 0.1 65

1 65

10 65

100k 0.1 65

1 65

10 65

C-26
Table 10.3.9B. Residual Distortion and Noise

(Above 10 Volts)

Low-Distortion Oscillator UUT Indication Accept. Limits

Freq.

Input level to

UUT Norn. Distortion Min

.

Hz V dB dB

20 100 65 dB

200 100 65 dB

2k 100 65 dB

20k 100 -=“

65 dB

100k 100 65 dB

C-27

APPENDIX D

ARBITRARY WAVEFORM PROGRAM

FOR USE WITH WAVETEK 275

SIGNAL GENERATOR

D-1
10 ! WAVETEK 2

20 ! ARBITRARY WAVEFORM PROGRAM FOR USE

30 ! WITH WAVETEK 275 SIGNAL GENERATOR

40 ! JUNE 4,1984

50 1 60 ! COMMENTS

70 ! OUTPUTS TWO WAVEFORMS TO THE WAVETEK. THEN SWITCHES FROM

80 ! SIGNAL WITH NO HARMONICS TO THE ONE WITH HARMONICS. AUG

90 1 100 1 no Lf$=CHR$(10) 1 LINE FEED

120 Ff$=CHR$(12) 1 FORM FEED

130 DIM M1(2000),M2(2000) ! HOLDS WAVEFORMS

140 N=180 ! DEFAULT NUMBER OF STEPS

150 N 1=N-1

160

170 ! INITIALIZE WAVEFORM GENERATOR

180 i 190 ON TIMEOUT 7,1 GOSUB No wavetek! HANGS IF TIME < 0.2C SEC

200 Wavetek=709

210 OUTPUT Wavetek; "P1G1S5.5E-6A5C6XB0XH",N 1,"I"

220 Pl=l ! OUTPUT ON

230 G=1 ! INTERNAL TRIGGER

240 S=2.67E-6 ! CLOCK PERIOD

250 A=5 ! 5V P-P INTO 50 OHMS

260 P$="ON" ! OUTPUT IS ON INDICATOR

270 H1=0 ! HARMONIC FREQUENCY

280 H2=0 ! HARMONIC AMPLITUDE

290 Freq=1000 ! FREQUENCY lOOOHZ

300 Startadd=0 ! START ADDRESS IS 0

310 Stopadd=N-l ! STOP ADDRESS IS N-1

320 I 330 ! SET UP KEYS

340 1 350 ON KEY 0 LABEL "CALC DIST" GOSUB Distortion

360 ON KEY 1 LABEL "FUNCTION" GOSUB Func! SAMPLE NO. HARMONIC

370 ON KEY 2 LABEL "FREQUENCY" GOSUB Freq! SET FREQUENCY

380 ON KEY 3 LABEL "AMPLITUDE" GOSUB Ampl! SET AMPLITUDE OF P 390 ON KEY 4 LABEL "ON/OFF" GOSUB On off! SET OUTPUT ON/OFF

400 [ 410 GOSUB Print status! DISPLAY DEFAULT STATUS

420 1 430 GOTO 430 ! WAIT HERE FOR KEY TO BE DEPRESSED

440 I 450 Print status: 1 460 I 470 PRINT Ff$

480 PRINT "HARMONIC FREQ ";H1

490 PRINT "HARMONIC AMPL ";H2

500 PRINT "FREQUENCY ";Freq

D-2
510

520

530

550

560

570

580

590

600

610

620

630

640

650

660

670

680

690

700

701

710

720

730

740

750

760

770

780

790

800

810

820

830

840

850

860

870

880

885

890

895

900

910

915

920

930

1060

1080

1090

1100

1110

1120

1130

PRINT "AMPLITUDE ";A

PRINT "NUMBER OF STEPS ";N

PRINT "ON/OFF ";P$

j Func: ! CALCULATE NEW FUNCTION

I INPUT "ENTER NUMBER OF STEPS",

N

N_1=N-1

Stopadd=Startadd+N~l

Ql=N/4 ! QUARTER CYCLE SAMPLE NUMBER

Q3=3-^N/4 ! THIRD QUARTER SAMPLE NUMBER

GOSUB Freq ! UPDATE FREQ WITH NEW SAMPLE NUMBER

INPUT "ENTER HARMONIC NUMBER", HI

INPUT "ENTER HARMONIC AMPLITUDE” ,H2

H3=N/(2*H1) ! NUMBER OF SAMPLES IN HALF OF A HARMONIC CYCLE

PRINT Lf$;”COMPUTING FUNCTION"

MAT Ml= (0)

FOR X=0 TO N-1

M1(X)=SIN(2*PI*X/N)

M2(X)=M1(X)

IF X>Q1-H3 AND X<Q1+H3 THEN

M2(X)=M2(X)+H2*(C0S(H1*2*PI*(X-Q1)/N)+1)

END IF

IF X>Q3-H3 AND X<Q3+H3 THEN

M2(X)=M2(X)-H2*(C0S(H1*2*PI*(X-Q3)/N)+1)

END IF NEXT X Biggest=MAX(M2(*)) ! Smallest=MIN(M2(*)) ! Max ab=MAX(Biggest,-Smal lest

)

MAT Ml= (2047/Maxab)*Ml! SCALE WAVEFORM

MAT M2= ( 2047/Max ab)*M2! SCALE WAVEFORM

PRINT LfS;"OUTPUTING FUNDAMENTAL"

OUTPUT Wavetek;"XB",Startadd,+1000"XH",Stopadd,+1000"I"

OUTPUT Wavetek;"C6I" ! FUNC 6 - ARBITRARY WAVEFORM NO FILTER

IFOR X=0 TO N-1

OUTPUT Wavetek ; "K" , X+St art add , " L" , Ml ( X ) , " I" OUTPUT Wavetek ; " K" , X+St art add+lOOO , " L

"

, M2 ( X )

, " I

NEXT X OUTPUT Wavetek ;"MlMXB",Startadd,"XH",Stopadd," I"

IPRINT "Fundamental sent " DISP "Press ENTER to send HARMONICS " INPUT Q$

OUTPUT Wavetek; "YU"

IBEEP ! ANNOUNCE COMPLETION

GOSUB Print_status

RETURN

1 Freq: ! CHANGE FREQUENCY

D-3
1140 DISP "CURRENT FREQUENCY IS ";Freq;"HZ"

1150 INPUT "ENTER NEW FREQUENCY" ,Freq

1160 OUTPUT Wavetek;"S",l/Freq/N,"I"

1170 BEEP

1180 GOSUB Print status

1190 RETURN

1200 ! 1210 Ampl : ! CHANGE AMPLITUDE

1220 ! 1230 DISP "CURRENT AMPLITUDE IS ";A; "VOLTS"

1240 INPUT "ENTER NEW AMPLITUDE",

A

1250 OUTPUT Wavetek;"A";A;"I"

1260 BEEP

1270 GOSUB Print_status

1280 RETURN

1290 ! 1300 On off: ! TOGGLE SIGNAL ON AND OFF

1310 r

1320 IF P$="ON" THEN ! TURN SIGNAL OFF

1330 OUTPUT Wavetek;"POI"

1340 P$="OFF"

1350 ELSE ! P$="OFF" TURN SIGNAL ON

1360 OUTPUT Wavetek;"PH"

1370 P$="ON"

1380 END IF 1390 BEEP

1400 GOSUB Print_statu

1410 RETURN

1420 ! 1430 No_wavetek:PRINT "NO WAVETEK - PUSH CONTINUE " 1440 ! 1450 PAUSE

1460 RETURN

1470 ! 1480 Distortion: ! CALCULATE DISTORTION FOR 3:1 CREST FACTOR TEST

1490 ! FROM SPECTRUM ANALYZER READINGS

1500 ! 1510 PRINT Lf$," INPUT FUNDAMENTAL AMPLITUDE

1520 INPUT Fund

1530 PRINT Fund

1540 Sum_sq=0

1550 Ran__out = l 1560 PRINT "ENTER A ZERO TO END INPUT OF HARMONICS " 1570 FOR 1 = 1 TO 40

1580 PRINT "Input HARMONIC

1590 INPUT Harmonic

1600 PRINT Harmonic

1610 Sum sq=Sum_sq+Harmonic*Harmonic

1620 IF Tfarmonic=0 THEN

1630 1=40

1640 Ran_out=0

1650 END IF 1660 NEXT I

D-4
1670

1680

1690

1700

1710

1720

1730

1740

1750

1760

•

IF Ran out THEN BEEP 400,1

Noi S6=TQR( Sum_sq)

Total=SQR( Sum_sq+Fund*Fund)

Dist=20*LGT( Noise/Total

)

j IMAGE K,4D.2D,K,4D.2D,K

PRINT USING 1720; "DISTORTION = ";Dist;" dB

I RETURN

END

= ";100*Noise/Total %"

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APPENDIX E

LOW-PASS FILTER

E-1
1

0

k 1 00k 1 n

FREQUENCY (Hz)

3.6mH±5% 2.7mHi5%

Fig. E.1 Frequency Response & Schematic of Low-Pass Filter

Used in Tests 10.3.4 and 10.3.6.

E-2
APPENDIX F

TEST EQUIPMENT LIST

FOR

TS-4084 ( ) / G

DISTORTION ANALYZER

F-1
ITEM RANGE MODEL

AC Calibrator 100 mV to 100 V ac Fluke 5200A or equiv.

Power Amplifier 100 V to 175 V ac Fluke 5205A or equiv.

AC Voltmeter 10 mV to 175 V ac Fluke 8506A or equiv.

Arbitrary Waveform Gen. 20 Hz to 20 kHz Wavetek 275 or equiv.

488 Controller HP 9836 or equiv.

Active Filter 20 Hz to 100 kHz Wavetek 452 or equiv.

Low-Pass Filter -3 dB @ 200 kHz See Appendix E Osci 1 loscope 20 Hz to 300 kHz Tektronix 2445 or equiv.

Audio Oscillator 10 Hz to 1 MHz Tektronix F6504T or equiv.

600 ohm Feedthrough Term. ± 1% Tektronix 011-0092-00 or equiv

Frequency Counter 20 Hz to 1 MHz HP 5316A or equiv. | Spectrum Analyzer 50 Hz to 100 kHz HP 3585A or equiv.

Coupling Transformer 5 khz UTC-LS-34 or equiv.

LCR meter — HP 4262A or equiv.

Isolation Transformer — Topaz 91002-22 or equiv.

3 Wire / 2 Wire Power Order by Description

Adapter

Low-Distortion Oscillator 20 Hz to 100 kHz Tektronix SG 5010 or equiv.

600 '^1 Resistors ±5% 1/2 watt Order by Description or equiv.

100:1 Atten. Probe Tektronix P6007 or equiv.

Noise Generator 20 Hz to 100 kHz Wavetek 132 or equiv.
N8S-n4A REV. 2-«CI U.S. DEPT. OP COMM.

BIBLIOGRAPHIC DATA

SHEET (See instructions)

1, PUBLICATION OR

REPORT NO.

NBSIR 35-3269

2. Performing Organ. Report No, 722.

3. Publication Date Noveiaber, 1985

4. TITLE and subtitle

ELECTRICAL PERFORMANCE TESTS FOR AUDIO DISTORTION ANALYZERS

5. AUTHOR(S)

O.B. Laug, G.N. Stenbakken, and T. F. Leedy

6. PERFORMING ORGANIZATION (If joint or other than MBS. see instructions)

NATIONAL BUREAU OF STANDARDS

DEPARTMENT OF COMMERCE

WASHINGTON, D.C. 20234

7. ContracL^Grant No.

8. Type of Report & Period Covered

9. SPONSORING ORGANIZATION NAME AND COMPLETE ADDRESS (Street, City, State. ZIP)

10. SUPPLEMENTARY NOTES

I I Document describes a computer program; SF-185, FIPS Software Summary, is attached.

11. ABSTRACT (A 200-word or less factual summary of most si gnifi cant information. If document includes a significant

bibliography or literature survey, mention it here)

Electrical performance test procedures for audio distortion analyzers were developed

by the National Bureau of Standards for the U.S. Army Communications-Electronics

Command. The report provides detailed, step-by-step test procedures that are based

on specifications supplied by the Army for purposes of evaluating audio distortion

analyzer bid samples. Examples of data sheets and tables are also provided for

recording interim and final results.

The report discusses the philosoply of each measurement procedure with a view toward

providing an understanding of the basic metrology required to perform the measurements. In addition, the sources of measurement error are discussed. The primary

applications and basic principles of modern audio distortion analyzers are also

presented.

12. KEY WORDS (Six to twelve entries; alphabetical order; capitalize only proper names; and separate key words by semicolon

audio distortion analyzer; distortion analyzer; distortion; distortion specification;

and test procedures.

13. AVAILABILITY

vxi Uni imited

I ! For Official Distribution. Do Not Release to NTIS

i Order From Superintendent of Documents, U.S. Government Printing Office, Washington. D.C.

20402.

X5i Order From National Technical Information Service (NTIS), Springfield, VA. 22161

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PRiNTED PAGES

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