Bruel & kjaer 1013 User guide

Beat Frequency Oscillator Type

1013

·a

,.

~

A Beat

Frequency

Osciilator

covering

the

range

200

to

200ooo

Hz. The

instrument

is

designed

to

meet

the

numerous

requirements

of

a

signal

source

for

audio

and

supersonic

frequency

work

.

It

is

excellently

suited

both

for

electrical

and

electro-acoustical

measurements,

as

well

as

for

acoustic

and

supersonic

research.

BRUEL&KJ&R

Naerum. Denmark .

ey;j;

80

05

00

.

.;:;:'"

BRUKJA, Copenhagen . Telex: 5316

BB

1018

Beat Frequency

Oscillator

Type 1013

NOVEMBER

1965

Contents.

Page

1.

Description

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

General

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

Oscillator

and

Mixer

Section

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

Partial

Blocking

of

Frequency

Range

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

Output

Amplifier

Section

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

Power

Supply

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

2.

Control

Knobs,

Terminals

and

Shafts

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

11

3.

Operation

..............................

.

.........

.

....

..

.........

14

General

.....

.

...........................................

.

........

14

A.

Frequency

Calibration

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

14

B.

Operation

Using

the

Output

Terminals

marked

LOAD

............

15

C.

Operation

Using

the

Built-in

Output

Attenuator

..................

15

D.

Frequency

Modulation

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

E.

Automatic

Recording

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

17

F.

Partial

Blocking

of

Frequency

Range

............................

19

G.

Automatic

Regulation

of

the

Output

Power

. . . . . . . . . . . . . . . . . . . . . .

21

H.

Remote

Control

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22

I.

Trouble

Shooting

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22

4.

Combined

Units

..

.

.............

..

.............................

.

..

24

Automatic

Frequency

Response

Recorder

Type

3306 . . . . . . . . . . . . . . . . . . 24

Automatic

Frequency

Response

Recorder

Type

3328

............

.

.....

25

5.

Applications

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28

Electronic Measurements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28

Frequency

Response

Measurements

of

Four

Terminal

Networks

......

28

AC

Bridge

Measurements

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29

Automatic

Recording

of

Electrical

Impedance

....

.

.................

30

Frequency

Response

of

High

Quality

Amplifiers

. . . . . . . . . . . . . . . . . . . . 31

Acoustical Measurements

.........

. . .

..............................

32

Frequency

Response

of

Loudspeakers

(Tweeter) . . . . . . . . . . . . . . . . . . . . 32

Directional

Characteristics

of

Loudspeakers

. . . . . . . . . . . . . . . . . . . . . . . . 34

Recording

of

the

Frequency

Response

of

Sound

Projectors

..........

35

Directional

Characteristics

of

Projectors

................

.

...........

36

Recording

of

Frequency

Response

of

Hydrophones

.

.................

39

Mechanical Measurements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40

Automatic

Recording

of

Accelerometer

Frequency

Response

. . . . . . . . . . 40

6.

Specifications

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42

Description.

Gt>neral.

The

Beat

Frequency

Oscillator

Type

1013 is

designed

for

measurements

in

the

frequency

range

200-200ooo

Hz

and

consists

of

an

oscillator,

mixer,

and

an

amplifier

section.

It

works

on

the

heterodyne

principle

using

two

high-frequency

oscillators,

one

of

which

operates

on

a

fixed

frequency,

while

the

frequency

of

the

other

can

be

varied

by

means

of

a

variable

capacitor.

The

required

signal

frequency

is

obtained

as

the

difference

between

the

two

high

frequencies

and

can

be

read

off

a

large

illuminated

scale,

the

pointer

of

which

is

connected

to

the

variable

capacitor.

The

scale

is

logarithmic

and

graduated

from

200

to

200ooo

Hz,

and

in

addition

an

INCREMENTAL

SCALE

is

provided,

allowing

exact

frequency

selection

in

the

range

-500

to

+500

Hz

for

any

setting

on

the

main

scale.

The

frequency

adjustment

is

carried

out

by

obtaining

a

beat

between

the

fourth

harmonic

of

the

line

voltage

and

the

oscillator

voltage,

occurring

when

the

oscillator

is

tuned

to

this

frequency

and

the

push

-

button

marked

LINE

FREQUENCY

BEAT

FOURTH

HARMONIC

on

the

front

panel

is

pressed.

The

variable

capacitor

has

two

control

knobs,

one

of

which

is

directly

connected

to

the

capacitor

spindle

and

is

used

for

quick

setting

of

the

approximate

frequency.

The

other

will,

when

pressed,

rotate

the

spindle

with

a

ratio

of

1

to

5

and

allow

fine

tuning

to

the

desired

frequency.

A

worm

gear

permits

the

capacitor

to

be

tuned

automatically,

for

example

by

the

aid

of

the

motor

in

the

Level

Recorder

Type

2305.

The

mechanical

connection

to

the

Level

Recorder

is

effected

by

means

of

a

flexible

shaft

which

can

be

screwed

onto

the

bushing

on

the

side

of

the

Oscillator

cabinet.

The

worm

gear

can

be

engaged

and

released

with

the

aid

of

a

built-in

electromagnetic

clutch,

operated

from

a

switch

on

the

front

panel

marked

AUTOMATIC

SCANNING

or

by

a

remote

control

arrangement

.

The

electro-

magnetic

clutch

is

a

friction

device,

so

that

manual

tuning

of

the

variable

capacitor

is

possible

even

when

the

clutch

is

engaged.

The

Beat

Frequency

Oscillator

is

provided

with

frequency

modulation.

A

reactance

tube,

controlled

by

saw-tooth

oscillations

from

a

built-in

oscillator,

may

be

switched

into

the

circuit

of

the

fixed

oscillator.

The

frequency

of

the

saw-tooth

oscillator

is

controlled

by

the

switch

marked

MODULATION

FREQUENCY,

and

the

amplitude

of

the

saw-tooth

oscillations,

which

controls

the

frequency

deviation,

is

regulated

by

FREQUENCY

DEVIATION.

Provision

is

also

made

for

external

modulation

whereby

very

wide

limits

of

frequency

modulation

can

be

obtained.

3

By

means

of

a

level

regulator

circuit

(COMPRESSOR)

which

can

be

con-

trolled

from

an

external

voltage,

it

is

possible

to

keep

the

voltage

current,

or

sound

pressure

constant

during

measurements,

when

the

oscillator

is

being

used

as

a

power

source,

(LOAD).

Oscillator

and

Mixer

Section.

Fig. 1.1

shows

a

block

diagram

of

the

complete

Oscillator.

The

diagram

is

divided

by

means

of

a

dotted

line

showing

the

oscillator

and

mixer

section,

and

the

amplifier

section

respectively.

Fig. 1.1.

Block

diagram

of

the

BFO

1013.

The

fixed

oscillator

is

tuned

to

1.2· MHz

and

can

be

frequency

modulated

by

means

of

an

arrangement

also

shown

in

Fig.

1.1.

The

reactance

tube

circuit

acts

as

a

variable

inductance

and

the

modulation

swing

can

be

continuously

varied

from

0

to

±

2ooo

Hz

by

means

of

a

potentiometer

on

the

front

panel

of

the

apparatus

,

marked

FREQUENCY

DEVIATION.

By

means

of

the

switch

marked

MODULATION

FREQUENCY

the

frequency

of

the

built-in

saw-tooth

oscillator

may

be

chosen.

Frequencies

of

2-4-8-

16-32

and

64

Hz

are

available.

The

oscillator

is a

blocking

type,

tuned

to

approximately

7 MHz,

and

the

frequency

of

the

saw-tooth

oscillations

is

selected

by

the

changing

of

the

grid

resistor.

Provision

is

made

for

external

modulation,

for

which

the

external

generator

should

be

connected

to

two

terminals

of

the

jack

on

the

front

plate

marked

REMOTE

CONTROL.

For

external

modulation

a

voltage

of

approximately

5

volts

is

necessary

when

a

modulation

swing

of

.±

2ooo

Hz

is

required.

The

impedance

of

the

external

generator

must

be

low

(approximately

1 k.Q).

When

external

modulation

is

employed

the

switch

marked

MODULATION

FREQUENCY

must

not

be

in

position

"Mod.

Off"

as

in

this

position

of

the

switch

the

reactance

tube

is

cut

off.

A

variable

capacitor

of

60

pF,

inserted

in

the

tuned

circuit

of

the

fixed

oscillator,

and

operated

by

the

knob

marked

FREQUENCY

INCREMENT,

4

permits

exact

frequency

selection

in

the

range

.± 500

Hz

in

relation

to

the

setting

on

the

main

scale.

By

means

of

a

noiseless

switch

on

the

front

panel,

marked

OSCILLATOR

STOP,

the

voltage

on

the

anode

of

the

1.2 MHz

oscillator

can

be

disconnected.

This

arrangement

is

specially

provided

for

reverberation

measurements.

The

identical

operation

can

be

obtained

by

remote

control

,this

can

be

seen

from

the

circuit

diagram

of

the

Oscillator.

The

output

voltage

from

the

fixed

oscillator

is

fed

to

the

grid

circuit

of

a

pentode,

the

grid

bias

of

which

is

controlled

by

a

regulating

amplifier.

To

obtain

a

high

degree

of

regulation,

the

working-point

of

the

pentode

is

chosen

on

the

non-linear

portion

of

the

Ia-Eg

characteristic,

near

cut-off.

The

purpose

•30

Full

Indica-

t i

ng

Me

t

er

dB

deflection

--........

•20

Graduation

'"

[·

':

-

10

-20

-30

- 40

0

u.:

a:i

'li -50

0

>

::J

Q.

-60

::J

0

-

70

I I

--

~",

v

Distorted

Signal

---

--

.,

\

1--

\\

-.......,_

\\

~

\\

\ Maximum

dynamic

1\

range

of

""'\

C

ompressor

OUTPUT

LEVEL

~ ~

t::!:

control

turned

~

:n

0

dB

____.-

-----

-10 dB- \

1\\

-30dB-

_ -

r---

~

-50

dB

,

~

""'

~

\~

1

\

r

-~

\\.~

No

i

se

~

level

-of B.

F.a

.

7 6 5 4 3 2

1-~+1

2 3 4

L

Approx

.

3V

5 d

/6

22

61-

Relative

vari

ation

of

COMPRES

S

OR

INPUT

voltage

Fig. 1.2.

Regulation

characteristics for

different

positions

of

the

potentiometer

marked

OUTPUT

LEVEL.

5

of

this

circuit

is

to

control

automatically

the

output

of

the

Beat

Frequency

Oscillator

by

applying

an

external

voltage.

The

external

control

voltage

should

be

fed

into

the

screened

jack

marked

COMPRESSOR

INPUT

on

the

front

panel

of

the

Oscillator.

A

variable

potentiometer,

marked

COMPRESSOR

VOLTAGE is

inserted

in

the

input

circuit

of

the

regulating

amplifier

and

can

be

used

as

level

control

for

the

output

from

the

Oscillator,

when

automatic

regulation

is

employed.

The

regulating

amplifier

has

a

linear

frequency

characteristic

from

200

to

200ooo

Hz

and

should

have

an

input

signal

of

approximately

3

volts

on

the

grid

of

the

amplifier

tube

for

full

regulation.

The

input

impedance,

measured

across

the

terminals

of

the

jack

marked

COMPRESSOR

INPUT

is

approx

-

imately

10

kohms,

and

the

obtainable

range

of

regulation

is

at

least

45 dB.

The

amplified

control

voltage

is

rectified

in

a

full-wave

double-diode

rectifier,

designed

to

give a DC

output

voltage

proportional

to

the

average

value

of

the

control

voltage.

The

speed

of

regulation

can

be

varied

with

the

switch

marked

COMPRESSOR

SPEED

on

the

front

panel

of

the

Oscillator.

Regulation

speeds

of

30-

100-

300

or

1ooo

dB/

sec

may

be

chosen

by

changing

the

value

of

the

capacitor

in

the

R-C

filtering

network

for

the

rectified

control

voltage.

When

the

switch

COMPRESSOR

SPEED

is

in

position

COMP.

OFF

the

output

from

the

recti-

fier

is

short-circuited

thereby

disconnecting

the

automatic

regulation.

It

is

also

possible

to

obtain

different

regulation

characteristics

dependent

on

the

position

of

the

potentiometer

marked

OUTPUT

LEVEL.

This

can

be

seen

from

Fig.

1.2.

To

obtain

good

regulation

even

when

maximum

output

power

is

required

from

the

Oscillator,

the

level

of

the

high

frequency

voltage

from

the

1.2 MHz

fixed

Oscillator

is

raised

approximately

10 dB

when

the

automatic

regulation

is

switched

in.

The

anode-circuit

of

the

pentode

in

the

variable

,

a-amplifier

is

tuned

to

1.2 MHz,

thereby

forming

a

band-pass

filter,

the

output

of

which

is

fed

to

the

mixer.

The

frequency

of

the

variable

oscillator

can

be

continuously

altered

from

1.2

MHz

to

1.0 MHz

by

means

of

a

specially

designed

variable

capacitor.

This

capacitor

is

made

with

a

high

degree

of

accuracy

and

a

maximum

deviation

of

o.7

degrees

from

a

logarithmic

frequency

curve

is

obtained.

The

Frequency

Main

Scale

can

be

remotely

scanned

via

a

mechanical

drive.

The

arrangement

is

intended

to

be

driven

from

the

B & K

Level

Recorder

Type

2305

via

the

Flexible

Shaft

UB 0041

(1

meter).

In

this

manner

the

frequency

scan

of

the

B.F.O.

can

be

driven

in

synchronism

with

the

pre-print

of

the

recording

paper

of

the

Level

Recorder.

The

built-in

worm

gear,

having

a

ratio

of

50 :1,

causes

a

scale

pointer

movement

corresponding

to

one

octave,

when

the

input

drive

of

the

B.F.O.

turns

through

three

revolutions

.

The

worm

gear

can

be

set

and

released

by

a

magnetic

slutch

which

is

operated

from

a

switch

(AUTOMATIC SCANNING)

on

the

front

panel

of

the

6

Oscillator,

or

it

can

also

be

operated

from

an

external

switch

or

relay.

In

the

latter

case

connection

must

be

made

to

the

appropriate

terminals

of

the

jack

marked

REMOTE

CONTROL

on

the

front

panel,

and

the

control

switch

AUT. SCANNING

for

the

magnetic

clutch

must

be

in

position

"Off".

By

means

of

a

pushbutton

marked

10ooo

Hz

REF.

SIGNAL,

an

extra

capacitor

is

introduced

in

the

tuning

circuit

of

the

variable

oscillator.

There

viii

be

exactly

lOooo

Hz

at

the

output

socket

when

the

scale

pointer

is

set

to

10ooo Hz

REF.

SIGNAL

and

the

pushbutton

10ooo

REF.

SIGNAL

is

depressed.

The

reason

for

setting

the

scale

pointer

at

10ooo

Hz

REF.

SIGNAL is

in

order

to

be

able

to

align

the

1013

with

the

frequency

calibrated

paper,

used

on

the

Level

Recorder

Type

2305,

as

this

paper

is

calibrated

from

10 Hz.

The

distance

between

the

calibration

mark

of

10 Hz

and

20 Hz

on

the

recording

paper

corresponds

to

the

distance

between

1oooHz

REF.

SIGNAL

and

200Hz

on

the

oscillator.

By

depressing

the

pushbutton

it

is

now

possible

to

check

that

the

level

of

the

middle

frequencies

is

within

the

divisions

of

the

paper.

The

voltage

developed

across

the

grid

circuit

of

the

variable

oscillator

is

fed

to

the

mixer

tube

via

a

buffer

amplifier

stage.

This

stage,

which

prevents

undesired

coupling

between

the

fixed

and

variable

oscillator,

also

increases

the

signal

level

to

a

value

required

for

correct

functioning

of

the

mixer.

The

mixer

tube

is a

triode

giving a

low

hum

level

in

spite

of

the

AC

heating

of

the

filament.

A

low-pass

filter

with

a

cut-off

frequency

of

500

kHz

is

inserted

in

the

anode

circuit

of

the

mixer

tube,

passing

only

the

lower

frequency

obtained

by

the

frequency

conversion

to

the

grid

circuit

of

the

first

tube

in

the

output

amplifier

section.

Partial Blocking

of

Frequency Range.

As

previously

mentioned,

the

frequency

scale

is

logarithmic

and

calibrated

20Q-20ooo

Hz.

When

the

capacitor

is

set

to

frequencies

above

20ooo Hz

or

below

200

Hz

the

fixed

Oscillator

can

be

blocked,

and

consequently

no

output

voltage

will

be

obtained.

For

automatic

recording

of

frequency

characteristics,

i.e.

when

using

the

Level

Recorder

Type

2305,

this

is a

great

advantage

as

no

unwanted

curves

will

then

appear

on

the

corresponding

section

of

the

frequency

calibrated

paper.

The

cut-off

section

can

be

made

wider

by

adjusting

the

cam

discs,

connected

to

the

rear

end

of

the

capacitor

spindle.

It

is

possible

to

cut

down

the

fre-

quency

range

to

approximately

one

octave

in

any

part

of

the

range

of

200-200ooo

Hz.

However,

if

the

REMOTE

CONTROL

plug

is

removed

there

will

be

no

blocking

at

any

part

of

the

scale.

In

application

where

the

B.F.O. is

employed

in

conjunction

with

the

B & K

Level

Recorder,

and

where

automatic

recording

is

required,

the

blocking

arrangement

can

also

be

used

for

remote

lifting

of

the

Level

Recorder's

writing

pen.

This

is a

great

asset

in

for

example

measurements

where

the

7

compressor

circuit

of

the

B.F.O. is

used.

In

this

instance

the

pen-lifting

arrangement

of

the

Level

Recorder

can

be

controlled

from

the

frequency

blocking

circuit

by

making

the

appropriate

connections

to

the

REMOTE

CONTROL

jack

of

the

B.F.O.

In

cases

where

the

entire

frequency

range

(200-200ooo

Hz)

of

the

B.F.O. is

utilized,

the

normal

frequency

blocking,

which

functions

outside

the

scale

graduation,

should

be

set

out

of

operation.

The

writing

pen

of

the

Level

Recorder

can

now

be

lifted

from

the

paper

outside

the

frequency

range

of

interest

and

a

proper

working

of

the

com-

pressor

also

at

the

initial

frequency

(2QO

Hz) is

ensured

during

the

automatic

scan.

If

the

described

methods

is

not

utilized,

the

following

would

take

place:

No

signal

will

be

present

in

the

range

200ooo

Hz

to

200

Hz

(outside

the

scale

graduation),

i.e.

the

compressor

of

the

B.F.O.

will

be

in

such

a

condition

to

give

full

output

signal

of

the

B.F.O.

Consequently,

when

the

scale

pointer

goes

inside

the

scale

graduation

(200 Hz)

full

output

level

will

be

transmitted

at

200Hz,

and

after

the

chosen

time

delay

(COMPRESSOR

SPEED)

the

signal

level

will

be

compressed

to

the

proper

(preset)

value.

A

deflection

on

the

recording

paper

which

is

not

a

response

of

the

measured

object

would

thus

be

recorded.

Output Amplifier Section.

The

voltage

from

the

low-pass

filter

is

fed

to

the

control

grid

of

the

first

tube

in

the

two-stage

output

amplifier

via

a

variable

potentiometer.

This

potentiometer

is

operated

by

the

knob

marked

OUTPUT

LEVEL

on

the

front

panel

of

the

Oscillator

and

is

used

for

continuous

adjustment

of

the

output

power.

The

gain

of

the

amplifier

is

stabilized

by

negative

voltage

feedback.

The

anode

circuit

of

the

output

tube

is

coupled

to

the

impedance

matching

circuit.

Four

different

output

impedances

are

available

and

can

be

chosen

by

the

switch

on

the

front

panel

marked

MATCHING

IMPEDANCE.

The

different

positions

of

the

switch

are

indicated

by

6, 60, 600

and

6ooo

ohms

respectively

and

the

output

voltage

is

taken

from

the

terminals

marked

LOAD.

It

should

be

noted

that

the

output

impedance

of

the

Oscillator

is

only

approximately

20 %

of

the

indicated

values,

but

with

correct

loading

maximum

power

output

is

obtained

with

minimum

harmonic

distortion

(Fig. 1.3).

In

addition,

correct

loading

ensures

the

output

voltage

to

be

independent

of

the

frequency

to

within

± 1

dB

for

frequencies

between

200

and

200ooo Hz. A

fifth

position

of

the

switch

MATCHING

IMPEDANCE

is

marked

"Att."

and

connects

the

output

transformer

to

an

attenuator,

variable

in

steps

of

10 dB

from

400

fA-VOlts

to

12.5 volts.

The

attenuator

is

operated

by

the

switch

marked

ATTENUATOR

on

the

front

panel.

In

this

position

of

the

impedance

switch

the

output

circuit

is

connected

to

the

screened

jack

on

top

of

the

front

panel.

The

output

impedance

is

constant

and

approximately

50

ohms.

The

accuracy

of

the

attenuator

is

better

than

± 2

%.

The

voltage

on

the

output

terminals

is

indicated

by

a

vacuum-tube

voltmeter

8

BRUEL & KJAER 1013 User guide

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