NASA CR-132305 PROTOTYPE PARTIAL ONE-THIRD OCTAVE … · However, as frequency increases, the...

N A S A CR-132305

PROTOTYPE PARTIAL O N E - T H I R D O C T A V E B A N D SPECTRUM ANALYZER FOR A C O U S T I C , V I B R A T I O N AND OTHER W I D E B A N D DATA FOR FLIGHT

APPLICATIONS

O c t o b e r 1973

P r e p a r e d u n d e r C o n t r a c t NAS1-11823

P r e p a r e d b y : B o l t B e r a n e k and Newman I n c . 50 M o u l t o n S t r e e t Cambr idge , M a s s a c h u s e t t s 02138

P r e p a r e d f o r : N a t i o n a l A e r o n a u t i c s and Space A d m i n i s t r a t i o n L a n g l e y R e s e a r c h C e n t e r Hampton, V i r g i n i a 23365

https://ntrs.nasa.gov/search.jsp?R=19730023611 2020-02-22T19:59:49+00:00Z

N A S A CR-132305

PROTOTYPE PARTIAL O N E - T H I R D O C T A V E B A N D SPECTRUM ANALYZER FOR A C O U S T I C , V I B R A T I O N AND OTHER W I D E B A N D D A T A FOR FLIGHT APPLICATIONS

O c t o b e r 1973

P r e p a r e d u n d e r C o n t r a c t NAS1-11823

P r e p a r e d b y : B o l t B e r a n e k and Newman I n c . 50 M o u l t o n S t r e e t Cambr idge , M a s s a c h u s e t t s 02138

P r e p a r e d f o r :

N a t i o n a l A e r o n a u t i c s and Space A d m i n i s t r a t i o n L a n g l e y R e s e a r c h C e n t e r Hampton, V i r g i n i a 23365

FOREWORD

The equipment r e p o r t e d h e r e i n was c o n s t r u c t e d by Bo l t Beranek and Newman I n c . under Con t rac t NAS1-11823. Acknowledgement i s g iven to Byron E . Blanchard of BBN, who w a s r e s p o n s i b l e f o r t h e

c i r c u i t d e s i g n , and to Mr. Alfred Beswick o f Langley Research Cen te r who provided v a l u a b l e a s s i s t a n c e d u r i n g t h e performance o f t h e c o n t r a c t .

iii

ABSTRACT

The d e s i g n r e f inemen t o f a compact f requency a n a l y z e r f o r measurement and analysis on board f l i g h t v e h i c l e s i s dislaussed.

The a n a l y z e r has been c o n s t r u c t e d i n a p a r t i a l one - th i rd oc t ave band c o n f i g u r a t i o n w i t h s i x f i l t e r s and d e t e c t o r s spaced by t h e

from 316 Hz to 1 0 0 , 0 0 0 Hz and a broadband d e t e c t o r channe l . The a n a l y z e r has been t e s t e d ove r a t empera tu re range o f 40 t o 1 2 0 ° F a t a p r e s s u r e of one a tmosphere , and a t a t empera tu re of 75°F a t a n a b s o l u t e p r e s s u r e o f 1 x torr, and has demonstrated a t l eas t 6 0 d B o f dynamic r ange .

iV

T A B L E OF CONTENTS

Page

FOREWORD ................................................... iii ABSTRACT ................................................... i v

LIST OF FIGURES ............................................ v i

SECTION 1. I N T R ~ O D U C T I O N ................................... 1

2 . T E C H N I C A L DESCRIPTION .......................... 4 2 . 1 B u f f e r Ampl i f ie r .......................... 4 2 . 2 F i l t e r s ................................... 4 2 . 3 Low-Frequency Ac t ive F i l t e r s .............. 6 2 . 4 High-Frequency P a s s i v e F i l t e r s ............ 9 2.5 D e t e c t o r s ................................. 9 2 . 6 Gain Con t ro l Block ........................ 1 2

2 .7 E r r o r I n t e g r a t o r .......................... 16 2 .8 Level S h i f t e r ............................. 16

2.10 Summary ................................... 19 2.9 A G C D e t e c t o r .............................. 19

3 . TEST RESULTS ................................... 2 1

4 . CONCLUSIONS .................................... 5 1

APPENDIX A : Schematics and List of P a r t s .................. A - 1

B: Passive l / 3 Octave Band F i l t e r Design ......... B-1

C : P e r t i n e n t Data from t h e American S tanda rd S p e c i f i c a t i o n f o r Octave. Half.Octave. and Third-Octave Band F i l t e r Sets ................. C - 1

V

LIST OF F I G U R E S

F i g u r e 1.

2 . 3 .

4 . 5 . 6 . 7 . 8 . 9 . 10 . 11 . 1 2 . 1 3 . 1 4 . 15

1 6 . 17 9

18 . 1 9 .

......................... Analyzer c o n f i g u r a t i o n 2

.............. Block diagram o f p a r t i a l a n a l y z e r 5 Form and d e s i g n e q u a t i o n s f o r n e g a t i v e feedback Q i n s e n s i t i v e r e sona . to r (316 Hz and 1 0 0 0 Hz f i l t e r s ) .......................................... 7 Form and d e s i g n e q u a t i o n s f o r n e g a t i v e feedback Q i n s e n s i t i v e r e s o n a t o r (3160 Hz f i l t e r ) ....... 8

Form and d e s i g n e q u a t i o n s for h i g h f requency p a s s i v e f i l t e r s ................................ 1 0

O p e r a t i o n a l r e c t i f i e r .......................... 11

AGC d e t e c t o r r e sponse c u r v e s w i t h C A 3080 ...... 13

Gain c o n t r o l b lock ............................. 1 4

Error i n t e g r a t o r ............................... 17 Level s h i f t e r .................................. 18

AGC d e t e c t o r a n a l y s i s .......................... 20

Frequency r e s p o n s e of . 316 kHz channe l ......... 23

Frequency r e sponse o f 1 . 0 kHz channe l .......... 24

Frequency r e s p o n s e of 3.16 kHz channe l ......... 25

Frequency r e sponse of 1 0 kHz channe l ........... 26

Frequency r e sponse o f 31.6 kHz channe l ......... 27

Frequency r e s p o n s e of L O O kHz channe l .......... 28

Frequency r e sponse o f broadband d e t e c t o r ....... 2 9

L i n e a r i t y e r r o r ove r dynamic r ange of . 316 kHz channe l ........................................ 30

V i

L I S T O F FIGURES I c o n t . )

P

Figure 20.

2 1 .

22.

23

2 4 .

25

2 6 .

27 *

28.

L i n e a r i t y e r r o r ove r dynamic r ange o f 1 kHz channe l ................................. 31

L i n e a r i t y e r r o r ove r dynamic r ange of 3 .16 kHz channel ................................... 32

L i n e a r i t y e r r o r ove r dynamic r ange o f 1 0 kHz channel ......................................... 33

L i n e a r i t y e r r o r ove r dynamic r ange of 31.6 kHz channel .............................. 34

L i n e a r i t y e r r o r ove r dynamic r ange o f 1 0 0 kHz channel ................................... 35

L i n e a r i t y e r r o r ove r dynamic r ange of broadband d e t e c t o r a t 1 kHz ................... 36

Spot v e r i f i c a t i o n - f requency r e sponse of .316 kHz channel .............................. 37

Spot v e r i f i c a t i o n - f requency r e sponse of 1 . 0 kHz channel ............................... 38

Spot v e r i f i c a t i o n - f requency r e sponse of 3 .16 kHz channel .............................. 39

Spot v e r i f i c a t i o n - f requency r e sponse o f 1 0 kHz channel ................................... 40

Spot v e r i f i c a t i o n - f requency r e sponse of 31.6 kHz channel .............................. 4 1

Spo t v e r i f i c a t i o n - f r equency response of 1 0 0 kHz channel ............................... 4 2

Spot v e r i f i c a t i o n - f requency r e sponse of broadband d e t e c t o r channel .................... 43

Spot v e r i f i c a t i o n - l i n e a r i t y e r r o r over dynamic range of .316 kHz channel ............. 4 4

v i i

L I S T O F F I G U R E S (eont.1

F i g u r e 34 . Spot v e r i f i c a t i o n . l i n e a r i t y e r r o r ove r dynamic r a n g e of 1 kHz channe l ......................... 45

35 . Spot v e r i f i c a t i o n . l i n e a r i t y e r r o r ove r dynamic r ange o f 3.16 kHz channe l ...................... 46

36 . Spot v e r i f i c a t i o n . l i n e a r i t y e r r o r ove r dynamic r ange of 1 0 kHz channe l ........................ 47

37 . Spot v e r i f i c a t i o n . l i n e a r i t y e r r o r ove r dynamic r ange o f 31.6 kHz channe l ...................... 48

38 . Spot v e r i f i c a t i o n . l i n e a r i t y e r r o r ove r dynamic r ange of 1 0 0 kHz channe l ....................... 49

39 . Spot v e r i f i c a t i o n . l i n e a r i t y e r r o r ove r dynamic r ange of broadband d e t e c t o r a t 1 kHz ........... 50

A.1 . Analyzer assembly, low f r equency ............... A-2

A.2 . Analyzer assembly. h igh f r equency .............. A-3

A.3 . P r i n t e d c i r c u i t assembly No . 1 ................. A - 4

A.4 . P r i n t e d c i r c u i t a s s e m b l y No . 2 ................. A-5

A.5 . P r i n t e d c i r c u i t assembly No . 3 ................. A-6

A.6 . Low-frequency schemat i c ........................ A - 7

A.7 . High-frequency schemat ic ....................... A-9

A.8 . 3.16-kHz schemat ic ............................. A - 1 1

A.9 . Broadband schemat ic ............................ A-13

v i i i

1 . I N T R O D U C T I O N

Acous t ic and v i b r a t i o n measurements made on f l i g h t v e h i c l e s o f t e n r e q u i r e wideband data. Such data are u s u a l l y t e l e m e t e r e d or s t o r e d on-board f o r f r equency a n a l y s i s a t a l a t e r t i m e . How- e v e r , t e l e m e t r y and magnet ic t a p e data bandwidths are l i m i t e d , t h u s imposing r e s t r i c t i o n s on t h e amount of wideband data t h a t can be c o l l e c t e d on any one f l i g h t . Hence, t e c h n i q u e s f o r o b t a i n - i n g t h e e s s e n t i a l i n f o r m a t i o n c o n t e n t o f wideband data and con- v e r t i n g i t i n t o more t y p i c a l narrowband d a t a t h a t can be commu- t a t e d , t r a n s m i t t e d , o r s t o r e d can be ve ry u s e f u l .

I n t h i s program, a p a r t i a l one- th i rd-oc tave band a n a l y z e r f o r f r equency bands between 316 Hz and 1 0 0 kHz was de- s i g n e d and b u i l t , u s i n g a c t i v e f i l t e r s f o r t h e lower f r e q u e n c i e s (316 Hz, 1 0 0 0 Hz , 3160 Hz) and p a s s i v e f i l t e r s f o r t h e h i g h e r f r e q u e n c i e s ( 1 0 kHz, 31.6 kHz, 1 0 0 kHz). The a n a l y z e r per forms a f requency a n a l y s i s o f t h e wideband data on-board t h e v e h i c l e . Its o u t p u t i s a s lowly-vary ing s i g n a l t h a t i s compat ib le w i t h t h e na r - rower bandwidths 'of s t a n d a r d equipment , b u t which s t i l l c o n t a i n s t h e e s s e n t i a l f requency-ampl i tude i n f o r m a t i o n o f t h e o r i g i n a l wideband data.

To perform such a spec t rum a n a l y s i s e f f e c t i v e l y , an a n a l y z e r must be capab le of h a n d l i n g a very wide r ange o f i n p u t s i g n a l s . The d e s i g n s u t i l i z e d i n t h i s a n a l y z e r can a c c e p t s i g n a l s w i t h a r ange o f ampl i tudes v a r y i n g by a f a c t o r g r e a t e r t h a n 1 0 0 0 ( i . e . , 60 d B ) and compress t h i s i n f o r m a t i o n i n t o 1 2 dB/vol t a t t h e ou t - pu t (a r ange o f f i v e volts).

The spec t rum a n a l y z e r and i t s c i r c u i t r y a r e d e s c r i b e d i n d e t a i l i n Sec . 2 of t h i s r e p o r t . S e c t i o n 3 p r e s e n t s t h e r e s u l t s o f t empera tu re and p r e s s u r e t e s t i n g o f each o f s i x f i l t e r s and one broadband d e t e c t o r and a s s o c i a t e d c i r c u i t r i e s which comprise

1

W 0 z w E w LL w E

G

z 0

i- Q CY

H

3 c3 H

2

the partial analyzer. The tests determined the frequency- amplitude response characteristics at temperatures of 4OoF, 70°F, and 120'F at pressures of one atmosphere and 1 x lom6 torr.

3

2. T E C H N I C A L D E S C R I P T I O N

The frequency range of interest for the analyzer was specified to extend from 316 Hz to 100 kHz and the amplitude levels of signals within this range were specified to permit a variation of 60 dB. analyzer design and investigate whether different technologies

It was necessary to evaluate a prototype spectrum

. and/or recent technological advances currently available are better suited for the partial analyzer. Design considera- tions including size, weight, and power consumption were weighed against potential performance gains in determining the final design configuration.

A block diagram of the partial analyzer is shown in Fig. 2 and each of the blocks is described below.

2 . 1 Buffer Ampl i f i e r

A unity-gain buffer amplifier in each filter section pro- vides an impedance matching function from the high output impedance of the transducers to the relatively low impedance levels required by the filters. The buffer amplifier is internally connected to operate as a voltage follower.

2 . 2 F i l t e r s

All of the filters are designed to meet or exceed the American Standards Association Specification S1.11-1966 One-Third Octave Band Filter, Class 11. A copy of this specification is appended to the report.

4

BUFFER 113 OCTAVE AGC LEVEL AMPS BAND-PASS DETECTORS SHIFTERS

INPUT

FIG. 2. B L O C K D I A G R A M OF P A R T I A L A N A L Y Z E R

5

2 . 3 Low-Frequency A c t i ve F i 1 t e r s

Two v e r s i o n s o f a n e g a t i v e feedback r e s o n a t o r c i r c u i t w i t h

low "Q" s e n s i t i v i t y are used f o r t h e low f requency f i l t e r s . The g e n e r a l form of t h e c i r c u i t f o r t h e 316 Hz and lOU0 Hz f i l t e r s and i t s b a s i c d e s i g n are shown i n F ig . 3. I n F i g . 4 t he c i r c u i t used f o r t h e 3160 Hz t ' i l t e r and i t s b a s i c d e s i g n e q u a t i o n s are shown. The a m p l i f i e r g a i n r e q u i r e d i s p r o p o r t i o n a l to t h e squa re of Q, s o t h e maximum Q a v a i l a b l e i s s e v e r e l y l i m i t e d

by t h e ga in . The a m p l i f i e r feedback c i r c u i t i s o f high-pass form so compensation i s r e q u i r e d f o r 1 0 0 % feedback a t low f r e q u e n c i e s .

The combinat ion o f h i g h g a i n and d r a s t i c compensation l i m i t s t h e u s e f u l n e s s of e i t h e r c o n f i g u r a t i o n to low f r e q u e n c i e s . How- e v e r , w i t h i n i t s range (up to 5 or 1 0 kHz) e i t h e r c i r c u i t has

s e v e r a l advantages : t o t a l i n s e n s i t i v i t y of Q to small component va lue changes, low s e n s i t i v i t y of Q to a m p l i f i e r g a i n . The

c i r c u i t shown i n Fig. 3 u s e s an e m i t t e r f o l l o w e r c o n f i g u r a t i o n w i t h u n i t y g a i n for t h e f i r s t a m p l i f i e r and one-half o f a d u a l o p e r a t i o n a l a m p l i f i e r for t h e second a m p l i f i e r . The c i r c u i t shown i n F ig . 4 d i s p e n s e s w i t h t h e e m i t t e r f o l l o w e r while r e t a i n i n g t h e second a m p l i f i e r . I n e i t h e r c a s e , each complete f i l t e r con- s i s t s of two s e c t i o n s , tuned to 0 .92 and 1.08 t imes t h e nominal c e n t e r f requency , w i t h Q of 6 . 1 ; t hese v a l u e s p rov ide a maximally- f l a t one - th i rd oc t ave band f i l t e r , i . e . , 26% bandwidth .

6

a.

IN OUT

D

2 - A i A * = 4Q -1

OUT

F I G . 3. FORM AND D E S I G N E Q U A T I O N S FOR N E G A T I V E F E E D B A C K Q I N S E N S I T I V E RESONATOR ( 3 1 6 H z AND 1000 H z F I L T E R S )

7

IN

1

OUT

FIG. 4. FORM AND D E S I G N E Q U A T I O N S FOR N E G A T I V E F E E D B A C K Q I N S E N S I T I V E RESONATOR (3.16 kHz F I L T E R )

8

2 . 4 High-Frequency Pass ive F i l t e r s

The f i l t e r s w i t h nominal c e n t e r f r e q u e n c i e s of 10 kHz, 31.6 kHz, and 1 0 0 kHz were b u i l t u s i n g the p a s s i v e c i r c u i t r y shown i n F i g . 5 . The r e s i s to r s , c a p a c i t o r s , and i n d u c t o r s used a r e o f s u r f i c i e n t q u a l i t y t o be s t ab le o v e r t h e t empera tu re r ange and r e q u i r e a minimum of compensat ion f o r i n t e r n a l losses. The p a s s i v e f i l t e r s are des igned f o r a 23% bandwidth.

2 . 5 De tec to r s

Tne b a s i c d e t e c t o r , which i n s i m p l e s t form i s j u s t a d iode r e c t i f i e r , i s c r u c i a l t o t h e performance o f any a n a l y z e r con- f i g u r a t i o n . To r educe t h e e r r o r s due t o the o f f s e t b i a s i n g v o l t a g e r e q u i r e d by t h e d i o d e , a n o p e r a t i o n a l a m p l i f i e r i s commonly used. I n t h i s c i r c u i t t h e d iode i s connected i n s i d e t h e feedback l o o p of t h e o p e r a t i o n a l a m p l i f i e r as shown i n F i g . 6 . The open loop g a i n o f the a m p l i f i e r r educes t n e d iode v o l t a g e drop .

However, as f requency i n c r e a s e s , t h e r i n i t e s l e w i n g ra te o f t h e a m p l i f i e r o u t p u t and t h e n e c e s s i t y f o r t n e a m p l i f i e r o u t p u t v o l t a g e to t r a v e r s e two d iode d rops f o r each p o l a r i t y r e v e r s a l of t h e s i g n a l cause i n c r e a s i n g l y l a r g e e r r o r s i n t he

c i r c i u t o f F i g . 6 . 'l'he i 'requency r e sponse performance o f t h i s

c i r c u i t i s s t r o n g l y aependent on s i g n a l ampl i tude l e v e l and i s no t adequa te a t any s i g n a l l e v e l above about 80 kHz. c r e a s i n g the a m p l i f i e r compensat ion t o ach ieve a f a s t e r s l ewing ra te improves t h e f requency r e sponse performance. However, i t i s s t i l l s t r o n g l y dependent on s i g n a l ampl i tude l e v e l .

In-

9

F I G . 5 . FORM AND D E S I G N E Q U A T I O N S FOR H I G H FREQUENCY P A S S I V E F I L T E R S

10

R l IN C3-+&b-

C R l

C R 2

F I G . 6 . O P E R A T I O N A L R E C T I F I E R

OUT

11

The f r equency r e sponse performance i s ex tended t o meet or exceed the r e q u i r e d s p e c i f i c a t i o n s a t a l l s i g n a l l e v e l s by add ing a s e p a r a t e grounded-base v o l t a g e - t o - c u r r e n t a m p l i f i e r a f t e r t h e o p e r a t i o n a l a m p l i f i e r . However, t h i s c i r c u i t i s n o t a c c e p t a b l e because of i t s s i z e , we igh t , and power consumption. I n s t e a d , a n o p e r a t i o n a l t r a n s c o n d u c t a n c e a m p l i f i e r (RCA C A 3080)

i s used and per forms a d e q u a t e l y w i t h t h e d e t e c t o r s i g n a l l e v e l h e l d c o n s t a n t by t h e AGC c i r c u i t d e s c r i b e d l a t e r . The f requency r e sponse performance c u r v e s f o r t h e d e t e c t o r u s i n g a CA 3080

are shown i n F i g . 7.

2.6 G a i n C o n t r o l Block

The g a i n c o n t r o l i s used i n t he AGC c i r c u i t con l ' i gu ra t ion to keep t h e d e t e c t o r s i g n a l - l e v e l c o n s t a n t and to p r o v i d e t h e

l o g a r i t h m i c f u n c t i o n f o r t h e s y s t e m . A s chemat i c of t h e g a i n c o n t r o l i s shown i n F i g . 8 . B a s i c a l l y , t h e AGC c i r c u i t r y d e r i v e s a c o n t r o l v o l t a g e re la ted to t h e o v e r a l l ampl i tude of t h e i n p u t s i g n a l and u s e s i t t o va ry the g a i n o f t h e a m p l i f i e r s o t h a t t he s i g n a l l e v e l a p p l i e d to t h e d e t e c t o r c i r c u i t remains e s s e n t i a l l y c o n s t a n t i n ampl i tude . The d e r i v e d v o l t a g e i s , a l though l a t e r s c a l e d and l e v e l sh i f tea , e s s e n t i a l l y t h e o u t p u t i n f o r m a t i o n o f a n a n a l y z e r channel .

'l'he o p e r a t i o n o f t n e c i r c u i t can be e x p l a i n e d as f o l l o w s . The i n p u t s i g n a l i s fed th rough i n p u t c a p a c i t o r C1 and r e s i s t o r R, to t n e g a t e o f t h e FET f o l l o w e r QIA

t i o n a l ampl i f i e r Anl. The use of t h e FET i n f r o n t of A H 1 i s t o reduce t h e i n p u t bias c u r r e n t o f A R 1 which f lows th rough the c u r r e n t s p l i t t e r and a p p e a r s a t t h e o u t p u t as a p p a r e n t c o n t r o l

and t h e n t o t h e opera-

12

f

4 /

P C

I

M

=z V

I c 3

v) w

H

W v)

W n

-lov ’

FIG. 8. GAIN C O N T R O L BLOCK

1 4

v o l t a g e f e e d t h r o u g h . The o u t p u t of A R 1 d r i v e s t h e c u r r e n t s p l i t t e r t r a n s i s t o r s Q

l e v e l de te rmined by Q,, a l o n g w i t h R d iode" . keeps t h e AC v o l t a g e a t t h e gate of QIA s m a l l and t h e AC c u r r e n t

i n Q c u r r e n t of Q i s e s t ab l i shed and c o n t r o l l e d by t h e i n p u t

3A v o l t a g e l e v e l . connected as a c u r r e n t s p l i t t e r . The base v o l t a g e g a i n o f t h e

c i r c u i t i s Rlo/R1.

and Q4 which are d r i v e n by Class AB w i t h t h e bias 3 and R8 making up a " v a r i a b l e 7

Feedback c u r r e n t , t h rough t h e t r a n s i s t o r s Q3A and Q4A,

n e a r l y e q u a l to t h e c u r r e n t i n R1. Thus, t h e AC c o l l e c t o r 3A

and Q are a matched p a i r of t r a n s i s t o r s &3A 3B

When t h e base v o l t a g e s o f Q and Q are unequa l , t h e r a t i o 3A 3B of t h e i r c o l l e c t o r c u r r e n t s i s e x p o n e n t i a l l y r e l a t e d t o t h e

i n t e r b a s e v o l t a g e f

where I2 and I1 are t h e r e s p e c t i v e c o l l e c t o r c u r r e n t s , q i s the charge o f a n e l e c t r o n , V i s t h e i n t e r P a s e v o l t a g e , k i s 8oltzrnann's c o n s t a n t , and T i s t n e a b s o l u t e t empera tu re . The t empera tu re dependence i s compensated f o r by a tempera ture- dependent v o l t a g e d i v i d e r c o n s i s t i n g of' r e s i s t o r s Rll and R12;

R12 has a p o s i t i v e t e m p e r a t u r e c o e f f i c i e n t whose v a l u e i s propor- t i o n a l t o t h e a b s o l u t e t e m p e r a t u r e . Thus i t i s shown i n F i g . 8 that t r a n s i s t o r s Q and Q i n t h e c i r c u i t form a p r e c i s e AC g a i n c o n t r o l w i t h a n e x p o n e n t i a l , or l o g a r i t h m i c , o p e r a t i n g c h a r a c t e r i s t i c . p o i n t of t h e g a i n c o n t r o l from s h i f t i n g as t h e s i g n a l ampl i tude

3A 3B

T r a n s i s t o r s QIIA and QIIB keep t h e DC o p e r a t i n g

l e v e l and t h e c i r c u i t g a i n change, i . e . , t h e y keep t h e c i r c u i t symmetr ical under a l l o p e r a t i n g c o n d i t i o n s .

2 . 7 Error I n t e g r a t o r

A schemat ic of t h e e r r o r i n t e g r a t o r i s shown i n F ig . 9 . I n o p e r a t i o n , t h e d i f f e r e n c e between t h e i n p u t through R1 and t h e r e f e r e n c e c u r r e n t th rough H2 i s i n t e g r a t e d and used t o c o n t r o l t h e g a i n b lock and d r i v e t h e l e v e l s h i f t e r . v e n t s t h e ou tpu t of AR1 swinging more n e g a t i v e t h a n the +1OV r e f e r e n c e v o l t a g e . of a d u a l o p e r a t i o n a l a m p l i f i e r .

CR1 pre-

I n t h e f i l t e r cnanne l s , AR1 i s one-half

2 . 8 Level S h i f t e r

'I'he ou tpu t l e v e l s h i f t e r A R ~ w i t h Q s h i f t s t he o u t p u t v o l t - 5 age t o ground as r e f e r e n c e , r a t h e r t h a n +1OV as r e f e r e n c e as i n a l l p r e v i o u s l y d e s c r i b e d c i r c u i t s . 'I'he l e v e l s h i f t e r f o r c e s t h e same c u r r e n t to flow i n R1 and K2 and a l s o keeps t h e r i g h t hand end of R, a t t1OV. R2 w i t h r e s p e c t t o ground i s 5/6 of t h e v o l t a g e a c r o s s H1 w i t h

r e s p e c t t o +lOV. The f a c t o r 5/6 comes Yrom t h e cho ice o f s c a l i n g of v o l t a g e vs dB; a t t h e ou tpu t 5 V r e p r e s e n t s 60 d B i n o r d e r t o b e compatiDle w i t h t e l e m e t r y i n p u t s . Tne r e s u l t i n g 1 2 dB/V i s i n c o n v i e n t f o r i n -p rocess t e s t i n g ; 1 0 dB/V i s pre- f e r r e d and s o i s chosen as t h e i n t e r n a l s c a l i n g . i n t h e schema- t i c o f t h e l e v e l s h i f t e r , F ig . 1 0 , AR1 i s t h e second ha l f of t h e d u a l o p e r a t i o n a l shared w i t h t h e e r r o r i n t e g r a t o r .

Tnus t h e ou tpu t v o l t a g e a c r o s s

16

+20v I

IN

I +20v I

FIG. 9. E R R O R I N T E G R A T O R

OUT

17

F I G . 10 . LEVEL SHIFTER

18

2.9 HGC Detec tor

The Automatic Gain C o n t r o l D e t e c t o r c o n f i g u r a t i o n c o n s i s t s o f a g a i n b lock , high g a i n a m p l i f i e r c o n s i s t i n g o f one u n i t y g a i n o p e r a t i o n a l a m p l i f i e r and one 60 d B o p e r a t i o n a l ampl i f i e r , a d e t e c t o r , and an e r r o r i n t e g r a t o r . The o u t p u t v o l t a g e o f t h e

e r r o r i n t e g r a t o r i s used as t h e AGC U e t e c t o r s y s t e m o u t p u t and s i n c e t he r e l a t i o n s h i p between t n e sys tem g a i n and t h e c o n t r o l v o l t a g e can b e made a lmost e x a c t l y l o g a r i t h m i c , o u t p u t can be

g i v e n d i r e c t l y i n dB. F i g u r e 11 shows t h e AGC D e t e c t o r c i r c u i t c o n f i g u r a t i o n s c n e m a t i c a l l y and a l s o shows t h e d i f f e r e n t i a l e q u a t i o n o f i t s r e s p o n s e .

2.10 Summary

An a n a l y z e r d e s i g n was completed which m e t t h e s p e c i f i e d performance r equ i r emen t s of o n e - t h i r d o c t a v e band frequency- ampl i tude a n a l y s i s rrom 316 Hz t o 100 kHz ove r a 60 dB dynamic range . A d d i t i o n a l l y , a wideband d e t e c t o r i s i n c l u d e d as a separate channe l f o r customer convenience. Tes t r e s u l t s which demonst ra te achievement of t h e d e s i g n g o a l s a r e p r e s e n t e d i n t he nex t s e c t i o n . The d e s i g n r e q u i r e d a c t i v e and p a s s i v e f i l t e r c i r c u i t c o n f i g u r a t i o n s t o cove r t n e f requency r a n g e . An au tomat i c g a i n c o n t r o l c i r c u i t was used t o conve r t t h e i n p u t s i g n a l l o g a r i t h m i c a l l y and r educe t h e range r equ i r emen t s on the d e t e c t o r s .

ERROR INTEGRATOR

Cl

OUTPUT INPUT

E z = E , E KES

E,= + IEel, at AR1 INPUT I = Q

assume E l > 6

FIG. 11. A G C D E T E C T O R A N A L Y S I S

20

3 . TEST RESULTS

A p a r t i a l a n a l y z e r s y s t e m c o n s i s t i n g of s i x one - th i rd o c t a v e band f i l t e r s and one wideband d e t e c t o r was f a b r i c a t e d and t e s t e d a c c o r d i n g t o program s p e c i f i c a t i o n s . A b l o c k diagram of t h e a n a l y z e r i s shown i n F i g . 2 . The s e t o f s i x f i l t e r s was s e l e c t e d to cove r t h e f requency r ange o f i n t e r e s t .

T r a n s f e r c h a r a c t e r i s t i c s of t h e f requency ampl i tude response o f t h e s y s t e m a r e shown i n F i g s . 1 2 t h rough 18. These c h a r a c t e r i s t i c s were p l o t t e d a t 4OoF, 75"F, and 120°F a t normal a tmosphe r i c p r e s s u r e . Fo r comparison pu rposes , t h e cu rves are f i t t e d to t h e data p l o t t e d a t 75°F o n l y . The o r d i n a t e s c a l e i s t he DC o u t p u t e x p r e s s e d i n d B a t t h e compression f a c t o r o f 1 2 dB/vol t ( i . e . , A10 d B = AO.833 V a t t h e o u t p u t ) . The data was t a k e n by a p p l y i n g a s i n e wave s i g n a l a t t h e i n p u t and r e c o r d i n g the o u t p u t of each channe l . The i n p u t s i g n a l , nominal ly 0 d B V , was a d j u s t e d f o r 5 V DC o u t p r i o r to p l o t t i n g t h e r e sponse f o r each f i l t e r . T h i s p rocedure i s j u s t i f i e d . L a t e r we show t h a t t h e o u t p u t o f e a c h f i l t e r i s w i t h i n t h e

l i m i t s o f t h e s p e c i f i c a t i o n .

F i g u r e s 19 t h rough 25 p r e s e n t data from t e s t s performed to es t ab l i sh t h e dynamic r ange and l i n e a r i t y of each channel ove r t h e t e m p e r a t u r e range a t normal a tmospher ic p r e s s u r e . Here t h e i n p u t i s a d j u s t e d e x a c t l y r e 0 dB/V and t h e o u t p u t i s t h e n r e c o r d e d . The i n f o r m a t i o n o b t a i n e d i s p l o t t e d as an e r r o r cu rve which r e a d i l y demons t r a t e s t h a t t h e f i l t e r channe l cQmpl ies w i t h

l i n e a r i t y and dynamic r ange r equ i r emen t s . every c a s e i s re t h e i d e a l ( i . e . , 0 d B V i n = 5 . 0 ~ 0 V DC o u t , -60 d B V i n = U.OU0 V DC o u t ) one r e a d i l y a c c e p t s that w e have

S i n c e t h e " e r r o r " i n

2 1

justified the procedure previously employed in determining the frequency response amplitude characteristics of the filters.

Successful testing of the analyzer system was concluded by determining that the filters operate correctly at 75°F at an absolute pressure of 1 x 10 t o r r . The results of these pressure tests are shown in Figs. 26 through 39.

-6

2 2

c B

E

2

c 0 c

N I:

Io l-l M

LL 0

w v, z 0 P

0 z w

N r-4

23

I I I I I

E c 0 c

w 3 v) v) w pf

a

a I I 1 1 I 1 rc!

O 0 In

0 0 0 0 Y T 7 I

c 0 I

-I W z z Q I u N L Y

0

4

LL 0

W v) z 0

v) W cr: 2- 0 z W 3 C Y W cr: LL

a

Cr) 4

a LL H

2 4

0 0 0

c-

0 0 I ? T ‘f 0 r 0

.-I w z z I u N I Y

w 4

M

LL 0

W

25

I I I I I

-

t E t 0 c

e

c i

I I I 1

I I I I I I I

0 0 0 0

0 0 r

B s

8

0 Y)

1 W z z a I V

N I Y

co w a

co rl

‘ a LL w

0 F

I I I I I

w 3 v) v) w B

I I I I I 0 0 0 0 e' Y c c 0 I

4 I 0

N I Y

0 0 4

LL 0

W fn z 0 a fn W IY

r 0 z W 3 C Y W IY LL

h 4

a LL H

0 I I I I I 3

l-

E

e

a t 0 1-

L L

4- 0

10

b .- x

II c

W

3 v, v, W

a

a

a

L L L L

0 0

n o

0 0

LL

0 (u

0

c

Q

I I I I I 0

I s ? P 0 F

0

0 0 F

0 r - -

N

A I Y

+ V 2 W 3 CY W II:

r - k

r-

0

c 0 0

E 0 I- u w I- w n n z 4 a n 4 0 cr2 a L 0

W v) z 0

v) W ez t 0 z w 3 CT W E L

n

a3 4

a L +.I

I I I I I I

0 40' F 0 75' F A 120° F

1

m

E O

U Y

z [r: w

- 1

- 60 - 50 -40 -30 -20 -10 0 + 10 INPUT (dBW

FIG. 19. L I N E A R I T Y E R R O R O V E R D Y N A M I C R A N G E O F . 316 k H z C H A N N E L

1

c Po

E O

0 Y

8 pc W

- 1

PRESSURE = 1 x ~ O - ~ TORR RE 1 ATM AT

0 40" F 0 75" F A 120" F

0 - 50 - 40 - 30 - 20 -10 INPUT (dBW

0

F I G . 20. L I N E A R I T Y ERROR OVER D Y N A M I C RANGE OF 1 k H z CHANNEL

I PRESSURE = 1 x TORR RE 1 ATM AT I 0 40° F 0 75O F A 120° F

- 60 - 50 -40 - 30 - 20 -10 0 INPUT (dBW

FIG. 21. L I N E A R I T Y E R R O R O V E R D Y N A M I C R A N G E OF 3.16 kHz C H A N N E L

32

-60, - 50 - 40 - 30 - 20, -10 , 0 + 10 INPUT (dBV)

FIG. 2 2 . L I N E A R I T Y ERROR OVER D Y N A M I C RANGE OF 10 k H z CHANNEL

33

PRESSURE = 1 ~ 1 0 " ~ TORR RE 1 ATM AT

0 75O F A 120° F

400 F

I I I I I I

-1

- 60 - 50 - 40 - 30 -20 -10 0 + 10 INPUT (dBW

F I G . 23. L I N E A R I T Y E R R O R O V E R D Y N A M I C R A N G E OF 31.6 k H z C H A N N E L

34

I I

0 40° F 0 75O F

0

-1

-

I

3 - 50 - 4-0 - 30 - 20 -10 0 + 1 INPUT (dBV)

FIG. 24. L I N E A R I T Y E R R O R O V E R D Y N A M I C R A N G E O F 100 k H z C H A N N E L

35

I I I I I I I

I 1 PRESSURE = 1 x ~ O - ~ TORR RE 1 ATM AT

A m ' t

I I I I I I I

-0 Y

K O 8 Qz w

-1

-60 - 50 - 40 - 30 -20 -10 0 INPUT (dBV)

-0 Y

K O 8 Qz w

-1

-60 - 50 - 40 - 30 -20 -10 0 INPUT (dBV)

F I G . 2 5 . L I N E A R I T Y ERROR OVER D Y N A M I C RANGE O F BROADBAND DETECTOR A T 1 kHz

2 L

b c

~E w c

I I I 1 I

I ? T Y 0 0 0 0 w

0 I I I 1 I

0 0 0 (u fo t 0

? 0

1 I I I

N I Y

co 4 c*)

LL 0

/.r N w I v,

z 0 Y

U a

I z 0 w I- Q V

LL

e w > I- O n v,

H

H

co N

CY

LL H

37

L h

b c

0

I I I 0 2 0 0 0 * Y c I

N

e

a! 0

00 d

m 0

s

8

0

a

2 W z z cr: I 0

N I Y

0

4

LL 0

W m z 0

m W er: >- 0 z W 3 W W oc LL

a

I z 0

b Q V

LL

oc W > I- O a v,

H

H

H

h N

a LL H

38

I I I I

I ? 7 0 0 0

v 0

> - n

D

c

0

D

d - - N I Y U

>. 0 z 3 0 w LI

r o w

a w CL L

I z 0 U

I- < u L U

U

w 5.

I-

39

0 t

L L.

c 0

0 I 2 x

I I I I I 0 0 0 0

Y c t O M In

I - 0 I

-I w z z Q I 0

N I Y

0 %-I

LL 0

w cn z 0 Q m W CL

>- 0 z W 3 cy W cr: LL

I z 0

I- 4: 0

LL

CL w > I- O 0- cn

U

U

U

m N

a LL H

40

I I I I I

I I I I I 0 0

I ? ? P 0 c 0

N cn I z

0 Q cn w

Y u

> e 0 z W 3 w a W U !z LL LL

I

r V z => W w

z 0

I- Q 0

LL

!z w > I- O a cn

H

H

H

0 Cr)

(3

LL H

0 0 0 0 Y c * - 0 I

NIP) i n d i n o

-1 W z z 4 I 0

N I Y

0 0 4

LL 0

W m z 0

m W cr: >- 0 z W 3 C Y W CL LL

a

I z 0

I- Q 0

LL

CL W > I- 0

v,

H

H

H

a

4 M

c3

LL H

4 2

I I I I I

f

43

I X PRESSURE = 1 x ~ O - ~ TORR RE 1 ATM AT 75O F-1

a 0

a 8 w

-1

+ 1 INPUT (dBV)

FIG. 33. SPOT V E R I F I C A T I O N - L I N E A R I T Y E R R O R O V E R D Y N A M I C R A N G E OF .316 kHz C H A N N E L

44

1

-1

-

m

-

II

-50 - 40 - 30 -20 -10 + 10 INPUT ‘(dBV)

FIG. 34. SPOT V E R I F I C A T I O N - L I N E A R I T Y E R R O R O V E ? D Y N A M I C R A N G E O F 1 k H z C H A N N E L

45

1

c m 0 Y

I I I I I I -- I X PRESSURE = 1 ~ l o - ~ TORR RE 1 ATM AT 75' F I

-60 - 50 -40 - 30 -20 -10 0 + 10 INPUT (dBW

F I G . 3 5 . SPOT V E R I F I C A T I O N - L I N E A R I T Y ERROR O V E R D Y N A M I C RANGE OF 3 . 1 6 k H z C H A N N E L

46

1

c m U U

g o a a W

-1

I X PRESSURE = 1 x l b 6 TORR RE 1 ATM AT 75' F I

-60 - 40 - 30 -20 -10 0 INPUT (dBW

3

FIG. 36. S P O T V E R I F I C A T I O N - L I N E A R I T Y E R R O R O V E R D Y N A M I C R A N G E O F 10 k H z C H A N N E L

47

INPUT (dBV)

F I G . 3 7 . S P O T V E R I F I C A T I O N - L I N E A R I T Y E R R O R O V E R D Y N A M I C R A N G E O F 31 .6 k H z C H A N N E L

48

1

P m U U

g o a a W

-1

-60 -50 - 40 - 30 -20 -10 0 + 10 INPUT (dBV)

-60 -50 - 40 - 30 -20 -10 0 + 10 INPUT (dBV)

FIG. 38 . w o - r V E R I F I C A T I O N - L I N E A R I T Y E R R O R O V E R D Y N A M I C R A N G E O F 100 kHz C H A N N E L

49

- 60 - 50 - 4 0 - 30 - 20 -10 0 '4 10 INPUT (dBV)

FIG. 39. S P O T V E R I F I C A T I O N - L I N E A R I T Y E R R O R O V E R D Y N A M I C R A N G E O F B R O A D B A N D D E T E C T O R A T 1 kHz

4. CONCLUSIONS

The d e s i g n , f a b r i c a t i o n , and t e s t work has s u c c e s s f u l l y pro- v ided a p a r t i a l o n e - t h i r d o c t a v e band a n a l y z e r of ex tended s i g n a l ampl i tude and f r equency r ange f o r u se on board high-speed endo- a tmospher ic and space f l i g h t v e h i c l e s . The technology developed s i g n i f i c a n t l y r e d u c e s t h e requi rement f o r wide dynamic r ange and wide bandwidth on t e l e m e t r y l i n k s o r on-board data s t o r a g e equipment when dynamic p r e s s u r e or v i b r a t i o n measurements are made.

A P P E N D I X A

S c h e m a t i c s a n d L i s t o f P a r t s

L L

I (3

I H

n

2-

0 N I

V U

tu

n h h e 0 W I 0 U

I-

3 V IY

V

U

W

n

h

co h

A-6

‘3 r

L I.

v)

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LL 1 3 0 J

a

0 a0 I n Y

W I U

c3

LL U

c

In

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h I

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4

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0

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N I Y I

W l-l

m

U

W W m 0 03 I n W

03

Q I

a L L U

i-i

4 I '

r-

1 4

Y t ' , L ? u

n

m n

z <

0 ct m

m r I I -

c3W

2. 0 z w =J W w

LL

3 0 -1

n

t. -1

v, v, Q

w N 2. -1 Q z 4

e 0 LL

v, I- = Q a LL 0

I- v,

-1 H

I Q

w -1 m 4 I-

N> I I -

c3G

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z rl 0

I- 0 a z e 3-1 0 v) vl w vl n 4

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ri

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W r- =T 0 W

I n

rl

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a

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W c- 3 0 W

I n

r- t- =r 0 \D I n

W Ln M rl M

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rn 4 =I-

=; X 0 co

I Q

co in M 0 co

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W W M 0 co

I n

. . . . 4 4 0 0 4 4 z z m z z

m 4 4 3 - 1 3 - 1

A-15

(v I

r l z m

PI

a w r l z

z 0 Y I- n.

PI u Ln W c3

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. . . . u v v v . . . .

z 9 0 u H H z z m

A-16

4

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W 0

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v) I- cr: 4 n

H

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M I 4

w -I m 4 I-

> e- 0 m I W

c- N e: LL w Lz

rl

J e:

rl

z 0 -

A-17

0 N I = ?

w r l a LLv) W W Z R

Y

N N N 4 4 Ln \o m 0

m b

rl ~ n ~ m ~ n o o h o m o r n o I c n ~ t - ; f w O o

0 o n o m u

rl 0 0

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Ln 0 rl

m

a z >- LL

c Z W R

Y

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U

0 z

r l d

M n " % Ln 3 3 w

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3 \ \ E - w d r l 4 \ M r l d - - E i

M X u

o r l \ o w w

- r l r l

,*"""w A

r l ~ ; f m r n

E+ rn W E+ E+ 4

E w 4 w rn

rn w e:

se rl

3 W \ d

M Ln rl N

rn W e:

P m

u 14

Crl 4 z 4 z 4 m

il 4 5 n

e: 0 E+ rn H rn z 4 e: E+

4 4 5 n

lc 0

H rn z E-r

%

2

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0

Frr 1 rn

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Ee L n

k 0 rl

PI 4 u

z 0

I- - Ly: 1 2 v) w

H

Y

n u H

u H

. . . . . r n r n r n r n r n w w w w w e:e:p:e:e:

CY 0 L L

a O Z 1 0 nu zI- << u

A H <LL

Z V W W

<v) z

Y Y

I-n.

rn 4 4 4 e: E- z w V

m rn 4 Crl

m J d w

4

rn

s 2

w 5 b 4

rn 2

0 u

E! 4 w

* I cl W A m 4 I-

O z

w I-

A - 1 8

3 r l r l m r l r l r l r l N r l 3 r l J N >

W c 3 . -

W

N

ix 0 LL

v, I- ix Q a LL 0

I- v,

-I H

0 z

m a

N m N 4 cr: e: c o * t + +

A - 1 9

A P P E N D I X B

P a s s i v e 1 / 3 O c t a v e B a n d F i l t e r Design

B-1

S T E P 1. C H A R A C T E R I Z E P R O T O T Y P E LOW P A S S F I L T E R

1R L n C out

e 1R in c~ - f -

f 2 4 1 = .2316 = a 1 fm

L = a J?-= 6.12 H

C = a 6*= 6.12 F

S T E P 2. T R A N S F O R M T O N O R M A L I Z E D B A N D P A S S F I L T E R

1R L2 I I

Radian Note: L,C, and L2C2 each resonate at 1

-37 which is most inconvenient since we want Problem! -

to use stock inductors.

Ll L2

B-2

S T E P 3. I M P E D A N C E TRANSFORM P O R T I O N OF C I R C U I T AROUND L, I N ORDER TO R E A L I Z E D E S I R E D L,/L,*

- 1 so L, = L, = 6.12H Choose - - L, L2

Replace 4;- 7''

cB With

Where CA = (l-n)C,

CB = n,C,

= n2 (C,+C,)-nC, cC 1

n=6.12 = .137F - 1

- 1 1 'A - m) 6.12 ' B - m * 6 . 1 2 = .0267~

*Guillemin, E.A., "Synthesis of Passive Networks,'! John Wiley & Sons, New York, 1957, pp. 141-157.

B- 3

S T E P 4. C O M P L E T E T H E I M P E D A N C E T R A N S F O R M A T I O N S T A R T E D IN S T E P 3 T O R E A L I Z E T H E P R O T O T Y P E B A N D P A S S F I L T E R

37 - 4Q 7 7 7 7 7

137F ,141F 6 .12H

T h i s i s a l / 3 OB f i l t e r w i t h a c e n t e r f requency o f 1 Radian/Sec and t e r m i n a t i n g r e s i s t a n c e s of 1 ohm and 37.4 ohms r e s p e c t i v e l y .

S T E P 5 . S C A L E T H E P R O T O T Y P E TO T H E D E S I R E D F R E Q U E N C Y A N D I M P E D A N C E L E V E L S

w = 2Tfm ( m i d band f requency ) m

- 1 CD - - LDw;

C A = 0.137 CD

cB = 0.267 C D

Cc = 0.141 CD

B-4

S T E P 6. CORRECT T H E R E S U L T S O F S T E P 5 FOR T H E L O S S E S I N T H E

I N D U CTO RS

Series Equivalent Circuit

0 UFr

4 - RS - - Q

Curves of Q vs frequency are given in data sheet for inductors.

Similarly, Parallel Equivalent Circuit

L P

G P

N L "= Lp = Ls for Q>>1

s o

Ri =

B-5

Ln - 8 - 1 .;f

x Ln

cy: I-i

rl

(\I

co 8-l 0

cy: M

G c co u c u

b u

!% c co m M

rl 0

G c t--

4 0

b 0

A 0 CI M

x =t b

cn

0 v, cu

!% c rl b

cu

G-i PI 0.l rl L n

El c M v,

0.l

0 v,

x E co

x B Ln

B-6

S T E P 7. T U N I N G A C T U A L F I L T E R

0

Because of component t o l e r a n c e s , CA and Cc w i l l have to be tuned i n the a c t u a l c i r c u i t as fol lows ( C B should be w i t h i n 5% of c o r r e c t va lue and d o e s n ' t need trimming).

To t r i m CA use t he fo l lowing c i r c u i t :

...

Short Cireu

.. T e s t Short

s c i l l a t c

7 7 7

Observe e 3 w i t h low capac i tance probe. peak i s a t fm.

Trim C A s o resonant Note t h i s i s a c t u a l c i r c u i t p l u s two jumpers.

T o t r i m Cc use t h e fo l lowing c i r c u i t :

7

Observe e2 and t r i m Cc s o resonant peak i s a t fm .

i s a c t u a l c i r c u i t w i t h two c u t s p l u s one e x t e r n a l r e s i s t o r . Note t h i s

i t !

e 2

B-7

A P P E N D I X C

P e r t i n e n t D a t a f r o m t h e A m e r i c a n S t a n d a r d S p e c i - f i c a t i o n f o r O c t a v e , H a l f - O c t a v e , and T h i r d - O c t a v e Band F i l t e r S e t s .

S1.11-1966

S p o n s o r e d b y t h e A c o u s t i c a l S o c i e t y o f A m e r i c a

A p p r o v e d May 4 , 1 9 6 6

A m e r i c a n S t a n d a r d s A s s o c i a t i o n I n c o r p o r a t e d

c-1

1. Purpose and Scope 1.1 Purpose. The purpose of this standard for filter sets is to specify particular bandwidths and characteristics which may be used to ensure that all analyses of noise will be consistent within known tolerances when made with similar filter sets meeting these specifications.

1.2 Scope. The standard for filter sets is suited to the requirements for analyzing, as a function of frequency, a broadband electrical signal. For acoustical measurements an electro-acoustic-transducer and amplifier are employed to convert the acoustic signal to be analyzed into the required electrical signal.

2. Definitions

These definitions are based upon those given in Ameri- can Standard Acoustical Terminology 1 Including Me- chanical Shock and Vibration), 51.1-1960.

2.1 Wave Filter (Filter). A wave filter is a transducer for separating waves on the basis of their frequency. It introduces relatively small insertion loss to waves in one or more frequency bands, and relatively large insertion loss to waves of other frequencies. (See 6.12 of American Standard Sl.1-1960.)

2.2 Band-Pass Filter. A band-pass filter is a wave filter that has a single transmission band extending from a lower Land-edge frequency greater than zero to a finite upper band-edge frequency.

NOTE: This definition is identical to !he definition in 6.15 of American Standard S1.l-1960 except that the words “band-rdge frequency” are substituted for “cutoff frequency.” Cutoff frequency in 6.16 of American Standard Sl.1-1960 is restricted to a frequency at which the response is 3 dB below the maximum response. In this standard the restriction does not apply to the frequencies limiting the passband. Therefore, the term “band-rdge frequency” IS used to avoid confusion. See 3.3 and Appendix B.

2.3 Filter Bandwidth. The bandwidth of a filter is the difference between the upper and lower band-edge frequencies, and defines the transmission band or pass band. In this specification the bandwidth is described by the interval in octaves between the upper and lower hand-edge frequencies.

2.4 Spectrum. The spectrum of a function of time is a description of its resolution into components, each of a different frequency and (usually) different in amplitude and phase. [See 1.34 ( I ) of American Standard S1.1- 1960.1 A Continuotls Spectrum is the spectrum of a wave the components of which Ere continuously distributed over a frequency rrgion. (See 1.37 of Ameriran Standard Sl.1-1960.) A White Noise .Spectrum is a continuous spectrum whose spectruii: density ( m e a n q u a r e amplitude per unit frequency) is independcnt of frequency over a specified frequency range.

2.5 ‘Tmnmishion 1,oss. ‘rriins1nission I,oss is the reduction in the mngnitrhe of sonic characteristic of a

signal, between two stated points in a transmission system. (See 4.29 of American Standard Sl.1-1960.)

NOTE I : In this specification the l i ansrn i s i~~n Lois is the rrdiiction in power levrl or voltagr levrl between the input applied IO the filter in series with its proprr input terminating impedance, and the outpiit delivrred I)y the filter to its proper load impedance.

NO’IE 2: in this spwification the Trunsrnimnn Loss (.harm- teristir of a filtrr, rrprrsenting thr change of Transmission lass with frequency, is specified with rcspect to the minimum Transmis- sion Loss in the passband measured when the filter is inserted between the proper terminating impedances.

NOTE 3: Attentration (not defined in American Standard SI . l- 1060) is frequently usrd as synonymous with Transmission Loss as defined above, in connection with filter charactrristics.

NO’I‘E .4: lnsertrorl h s s is a term also frequently used in connection with filters. The Insertion Loss resulting from insertion of a transducer in a transmission system is 10 times the logarithm to the base 10 of the power delivered to that p a r t - d the system that will follow the transducer, before insertion of the transducer, to the power delivered to that same part of the system after insertion of the transducer. (See 7.2 of American Standard Sl.1-1960.) For passive filters operated between resistive terminating impedances, the lnsertron LOJS Characteristic employing the minimtrm value as referent is the same as the Transrncssion Loss Characteristic.

2.6 Terminating Impedances. The terminating impedances are the impedances of the external input and output circuits between which the filter is connected.

2.7 Peak-to-Valley Ripple. When the transmission loss characteristic in the transmission band contains a series of maxima and minima, or ripples, the peak-to- valley ripple is defined as the difference in decibels between the extremes of minimum and maximum transmission loss in the pass band region.

3.1 Filter S e t s . The filter set shall provide a number of filter bands according to the schedules listed in Table 1, and shall bear the corresponding Type symbol:

R for Restricted Range E for Extended Range 0 for Optional Range

The filter bands are identified by the designation mean frequency f,,, of the band as defined in 3.2.

ean Frequency, f,,, 3.2.1 Band Designation Frequencies. The values of

mean frequency, f,, used for band designation in Table i are basrd upon the recommendations of 5.2, page 3, of Ameriran Standard S1.6-1960. Band designation frequencies shall be rounded according to American Stan- dard S1.6-1960.

3.2.2 Precise Valurs o f f , . Precise values of nominal mean frequency fm shall be calculated from the formulas given in Table 2.

3.3 Noininn1 Frequency Bandwidths. The nominal band-edge frequencies and bandwidths for the octave, half.octrrve, and third-octave band filters are defined by the relation3 given in Table 3. The frequency f,,, in each Lnnd is the geometric mean of the upper arid lower

c-2

nominal Land-edge frequencies, fl and fi, which are defined by Table 3. 3.4 Transmission I,oss vs Frequcricy Cfinracteristics of hidivitlual Filters. When tested as specified in Sec- tion 4, the separate filters of a set shall confornl to the requirements in the paragraphs below. For each filter characteristic, transmission loss is specified with respect to the minimum transmission loss in the frequency range f, t o f i delineated in Table 3. Transmission loss characteristics are grouped under three classes (I, 11, or 111)

depending upon the steepness of the slope of tht trans. mission loss vs frequency curve. Filter rIesi6nations must bear the appropriate Class symbol*

NO’I’I.;: In the transmission loss chars ristirs specified below, ttic mathematical statement is the govt’ ng condrrat ion. The graphical representation accompanying each characteristic re- quiremrnt is added for convenience. ‘I’he ;actual filter characteristic, in addition to falling within the transmission loss limits shown, must simultaneoiisly meet thr requirenients on Yasaband [lni- fwnii ty (see 3.6) and on Effective Uandwrdth (see 3.7). each plot a dotted curve i s shown as an example of a characteristic meeting all requirements.

Table 1 Table of Filter Bands To Be Provided

Mean Octave Bands Half-Octave Bands Third-Octave Bands Any Band Frequency Band

Number f , ( c / s ) Type R Type E Type R Type E Type R Type E Type 0

14 25 X

15 31.5 X X X

16 40 X

16.5 45 X

17 50 X

18 63 X X X

19 80 X

19.5 90 X

L e -

20 100 X X

21 125 X X X X X X

22 160 X X

22.5 180 X X

23 200 X X

24 2 50 X X X X X X

25 315 X X

25.5 3.55 X X

27 500 X X X X X X 5 28 630 x n

710 B 28.5 9

29 800 X 8 30 1000 X X X X X X v,

31 12.50 X X

31.5 1400 X X 4 2 32 1600 X X L.

33 2000 5 34 2500 X X zr,

0 2

26 400 X X 9 X X

X X

X P v)

X X X X X X

~~ -

34.5 2800 X X

35 3150 X X

36 4000 X X X X X X

37 5000 X X

37.5 5600 X

38 6300 X

39 80CO X X X

40 IO000 X

40.5 11200 X

41 12500 X

42 16000 X

43 21)000 X

c-3

3.4.1 O c t w c ~ Ilnricl Filters -Class I

( I ) A t any frcqwncy. f, in the rang(. from - to - Vm Ifm 4 .3

the transmission 105s shall not t ) r mor(* th;in

thr transmihsion loss shall be niorr than more thiin

c-4

TRANSMISSION LOSS dB

WITH RESPECT TO MINIMUM

TRANSMISSION LOSS

1.5 2 4 6 8 10 0.1 0.15 0.2 0.4 0.6 0.8 1 FREQUENCY RATIO - flf,

Fig. 1 Transmission Loss Limits -Octave Band Filter, Class I

(Filter Characteristic Must Also Meet Requirements in 3.6 and 3.7)

fm ( 2 ) At any frequency, f, in the r a g e from-to 2-"'fm

and from 2'l4fm to 6fm the transmission loss shall be more than

6

10 log,, [ ~t 250 (L --- >)I decibels.

f m ( 3 ) At any frequency, f, below - or above 6fm the 6 transmission loss shall be more than 70 decibels.

is given in Fig. 4. (4) A graphical representation of the allowable limits

3.4.5 Third-Octave Bond Filters -Class I1

(1 ) At any frequency, f, in the range from - to - 9fm lWm 10 9

the transmission loss shall not be more than

10 log,, [l t 1040 (- f - f m - ,'] decibels. f m f

fm ( 2 ) At any frequency, f , in the range from- to 2-"'f,,,

and from 2"'fm to 8fm the transmission loss shall be more than

8

10 log,, f f t 1040 (--- f - fm I] decibels. f m f

fm ( 3 ) At any frequency, f, below - or above 8fm the 8 transmission loss shall be more than 60 decibels.

is given in Fig. 5. ( 4 ) A graphical representation of the allowable limits

3.4.6 Third-Octave Band Filters -Class 111

(1 ) At any frequency, f, in the range from - to - 9 f m l o f m 10 9

the transmission loss shall not be more than

10 log,,: [I t 1040 (---)I f f m decibels. fm f

f m ( 2 ) At any frequency, f, in the range from- to 2-"'fm

and from 2"'fm to 5fm the transmission loss shall be more than

5

10 log,, [ - t 2500 (-- f --)I f m decibels. fm f

fm ( 3 ) At any frequency, f, below - or above 5fm the 5 transmission loss shall be more than 75 decibels.

is given in Fig. 6. ( 4 ) A graphical representation of the allowable limits

c-5



TRANSMISSION LOSS

LIMIT

~

0.1 0.15 0.2 0.4 0.6 a8 1 1.5 2 FREQUENCY RATIO - f/fm

Fig . 2 Transmission Loss Limits -0etnve Band Filter, Class IL

(Filter Characteristic Must Also Meet Requirements in 3.6 and 3.7)

MINIMUM

TRANSM l SSl ON LOSS dB


TRANSMISSION LOSS

-I----

TL > 6 0 d 8

-LLl: 4 6 0 10

B



TRANSMISSION LOSS

0.1 0.15 0.2 0.4 0.6 0.8 1 1.5 2 4 6 0 10



T R A N S M I S S I ON LOSS

FREQUENCY RATIO - f/f, Fig. 4

Transmission Loss Limits - Half-Octave Band Filter, Class HI (Filter Characteristic Must Also Meet Requirements in 3.6 and 3.7)

0.1 0.15 0.2 0.4 0.6 0.8 1 4 6 8 10 1.5 2

FREOUENCY RATIO - f/f, Fig. 5

Transmission Loss Litnits - Third-Octuvc: I h n c l Filter. Cluss I1 (Filter Characteristic Must Also Mvet ltequiremerrts in 3.6 and 3.7)

c-7

TRANS M I S SI 0 N Los s dB


TRANSMISSION LOSS

0.1 0.15 0.2 0.4 0.6 0.8 1 1.5 2 FREQUENCY RATIO .. f/f,

Fig. 6 Tmmsmiseion Loss Limits - TEzird-Qctave Band Filter, Class IiI (Filter Characteristic Must Also Meet Requirements in 3.6 and 3.7)

3.5 Frequency Tolerance on Geometric Mean Fre- quency. For each band designated on the filter set in accordance with Table 1 of 3.1 or its extension, the geometric mean of the two frequencies where the transmission loss is 6 dB greater than the minimum transmission loss shall not depart by more than the tolerances show-n in Table 4 from the designated preferred frequency nominal f;, calculated by the formulas of Table 2.

Table 4 Frequency Tolerances

on Geometric Mean Freqmncy, f,,, a

Octave Half-Octave Third-Octave Rands Bands Bands

PiJlrrnnce f 5% f 3% f 3% I_

3.6 Tolerance on Passband Uniformity. The peak- to-\ nllry ripple in the transmission loss characteristic hrtween the upper and lower nominal band-edge fre- qiwnc ics shull not exceed the values given in Table 5 far filters of the indicated bandwidths and classes.

3.7 EXfectise Bnndwiclth. For each filter band, the totnl 1ritvgr.rted rrsntiom white noise power (constant f)Oiw* p ! " c r per unit f r t p m c y ] passed by the filter shall h b i t h i i t d 1:: pcrciwt of that which would be passed by a n d r ~ l l i1ts. i wit t i flu1 pitss1)and between the nominal

C-8

4 6 8 1 0

band-edge frequencies of 3.3 and infinite attenuation outside the passband. The white noise power passed by such an ideal filter is given by:

2-'"/, P, = 0.707 lf,P, for Octave bands

(2"' - 2-'")fmP, = O.3483fmP, for Half-Octave bands

(21m - )f,P, = O.2316f,Pm for Third-Octave bands

where P , is the noise power per unit frequency at the filter midband frequency f,. The minimum transmission loss in the passband shall be used as the reference for calculating the effective bandwidth. -

NOTE: See Appendix B for the nominal band-edge frequency transmission loss required to produce zero bandwidth error for Butterworth filters.

Table 5 Tolerance on Passband U n i f o ~ ~ t y

, Maximum Allowabld Peak-to-Valley Ripple

Filter Band Filter Class dB

Octave all 2

Ha If-Oct ave I1 1

T hird-Oct a ve I1 1

Ill 0.5

111 0.5

i-

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