Brüel & kjær 1014 User guide

Beat Frequency Oscilla·tor Type

1014

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A

beat

frequency

oscillator

covering

the

range

20

to

20ooo

c/s. The

apparatus

is

designed

to

meet

the

numerous

requirements

of

a

signal

source

for

audio

frequency

work.

It

is

excellently

suited

both

for

electrical

and

electroacoustical

measurements,

as

well

as

for

acoustic

research

.

BHUEL&KJJEH

Nrerum,

Denmark

.

Phone

80

05

00

.

Telegrams:

BRUKJA,

Copenhagen

BB

10

14

Beat Frequency Oscillator

Type 1014

Reprint

January

1962

Contents

Description

5

General

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

Description

of

the

Oscillator

and

Mixer-Section

. . . . . . . . . . . . . . . . . . . . 6

Frequency

Marking

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

Partial

Blocking

of

Frequency

Range

. . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

Description

of

the

Output

Amplifier

Section

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

11

Power

Supply

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

13

Operation

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

14

General

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

14

Calibration

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

15

Operation

Using

the

Output

Terminals

Marked

"Load"

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

15

Operation

Using

the

Built-in

Attenuator

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

16

Frequency

Modulation

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

16

Automatic

Recording

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

16

Marking

Adjustment

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

20

Partial

Blocking

of

Frequency

Range

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

21

Automatic

Regulation

of

the

Output

Power

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

22

Remote

Control

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23

Trouble

Shooting

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23

Accessories

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24

Applications

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25

Group

A.

Electronic

Measurements

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25

Measurement

of

Frequency

Response

of

Four-Terminal

Networks

..

25

A.C.

Bridge

Measurements

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26

Measurements

of

Temperatures

and

Temperature

Differences

......

27

Measurement

of

Gain

in

A.F.

Amplifiers

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

30

Group

B.

Acoustical

Measurements

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30

Recording

of

the

Frequency

Response

of

Loudspeakers

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

30

Recording

of

the

Frequency

Response

of

Microphones

. . . . . . . . . . . . . 32

Recording

the

Frequency

Characteristic

of

Hearing

Aids

and

Ear-

phones

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

33

Checking

of

Hearing

Aids

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35

Measurements

on

Air

Filters,

Carburettor

Inlets

etc. . . . . . . . . . . . . . . . .

36

Testing

the

Qualities

of

Airborne

Sound

Insulation

. . . . . . . . . . . . . . . . 38

Measurement

of

Reverberation

Time

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39

Absorption

Qualities

on

Sound

Insulation

Material

. . . . . . . . . . . . . . . . 44

Group

C.

Mechanical

Measurements

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45

Strain

Measurement

on

Vibrated

Object

s

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

45

The

A.F.

Response

and

Spectrum

Recorder

Type

3326

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

47

Description

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

47

The

Audio

Frequency

Spectrometer

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

48

The

Level

Recorder

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49

Recording

Paper

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

50

Copying

of

Recorded

Information

........

.

....

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

51

Operation

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

52

General

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

52

Synchronization

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

52

Applications

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54

Automatically

Recording

Harmonics

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

. 54

Vibration

Measurements

...

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

.

..

57

Noise

Measurements

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

57

Specification

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59

Description

General.

The

Beat

Frequency

Oscillator

Type

1014 is

primarily

designed

for

electrical

and

electro-acoustical

measurements

and

consists

of

an

oscillator

-

and

mixer-

section

,

and

an

amplifier

section

.

It

works

on

the

heterodyne

principle

using

two

high

frequency

oscillators

,

one

uf

which

operates

on

a

fixed

frequency

,

while

the

frequency

of

the

other

can

be

altered

by

a

variable

capacitor.

The

required

audio

frequency

is

then

obtained

as

the

differenc

e

between

th

e

two

high

frequencies

and

can

be

read

off

a

large

illuminated

scale,

the

pointer

of

which

is

connected

to

the

variable

eapacitor.

The

scale

is

logarithmic

and

graduated

from

20

to

20ooo

c/s. An

"Incremental

Scale

" is

also

provided

,

allowing

exact

frequency

selection

in

the

range

-50 to

+50

c/s

around

any

se

tting

on

th

e

main

scale.

The

zero-adjustment

is

carri

ed

out

by

obtaining

a

beat

between

the

'

frequency

of

the

mains

voltage,

and

that

of

th

e

oscillator

voltage

occurring

''

when

the

oscillator

is

tuned

to

the

frequency

of

the

mains

and

the

pressbutton

marked

"

Power

Frequency

Beat

"

on

the

front

panel

of

the

oscillator

is

press~d.

The

variable

capacitor

has

two

control

knobs

,

one

of

which

is

in

a fixed

position

on

the

capacitor

spindle

and

is

used

for

quick

setting

to

the

de-

sired

frequ

ency.

The

oth

er will,

when

depressed

,

rotate

the

spindle

with

a

ratio

of

1

to

5

giving

greater

accuracy

and

final

selection

of

the

frequency.

A

worm

gear

permits

the

capacitor

to

be

tun

ed

automatically

,

for

example,

with

the

aid

of

the

motor

of

the

Level

Re

c

order

Type

2305.

The

mechanical

connection

to

the

Level

Recorder

is

effect

ed

by

means

of

a

flexible

shaft

which

can

be

screwed

onto

the

bushing

on

the

s

ide

of

the

Oscillator

's

cabinet

during

which

the

motor

should

be

kept

running

.

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,

or

by

a

remote

control

arrange-

ment.

The

electromagnetic

clutch

is a

friction-device

allowing

manual

tuning

of

the

variable

capa

c

itor

even

when

the

clutch

is

engaged.

Being

also

designed

for

use

in

room-acoustical

measurements,

the

Beat

Fre-

quency

Oscillator

is

equipped

with

frequency

modulation

,

for

which

a re-

actance

tube

controlled

by

saw-tooth

oscillations

from

a

built-in

oscillator

is

switched

into

tbe

circuit

of

the

fixed

oscillator.

Both

the

frequency

and

the

amplitude

of

the

saw-tooth

oscillation

are

adjustable

and

may

b~

read

off

two

printed

dials.

Provision

is

also

inade

for

external

modulation,

whereby

very

wide

limits

of

frequency

modulation

can

be

obtained.

By

means

of

a

compressor

circuit

,

which

can

be

controlled

from

an

externn.l

5

voltage,

it

is

possible

to

keep

the

voltage,

current,

or

sound

pressure

constant

during

measurements

when

using

the

oscillator

as

a

power

source.

Description

of

the

Oscillator

and

Mixer-Section.

Fig. 1

shows

a

block

diagram

of

the

complete

Oscillator.

The

fixed

oscillator

is

tuned

to

120

kc/s

and

can

be

frequency

modulated.

The

Fixed

Oscillator

Regulating

Amplifier

Variable

)J

Amplifier

Mixer

Low

Pass

Filter

Variable

Oscillator

Impedance

Output Matching

Amplifier Circuit

100

°

C(~

emote

Ref.

Sig.

L.~_Jfontrol

Magnetic :

Clutch 1

I

Output

Attenuator

Load

Output

Attenuator

Output

1605+6

Fig.

1.

Block

Diagram

of

the

Beat

Frequency

Oscillator 1014.

reactance

tube

circuit

acts

as

a

variable

inductance

and

the

modulation

swing

can

be

continuously

varied

from

0

to

± 200 c/s

by

means

of

a

potentiometer

on

the

front

panel

of

the

apparatus

,

marked

"Modulation

Swing

".

By

means

of

the

switch

marked

"Modulation

Frequency

"

the

frequency

of

the

built-in

saw-tooth

oscillator

may

be

chosen.

Frequencies

of

1- 2- 4- 8- 16

and

32 c/s

are

available

.

The

oscillator

is a

blocking

type,

tuned

to

approx-

imately

7 Mc/s,

and

the

frequency

of

the

saw-tooth

oscillations

is

set

by

changing

the

grid

resistor.

Provision

is

made

for

external

modulation.

The

external

generator

should

then

be

connected

to

two

terminals

of

the

socket

on

the

front

plate

marked

"Remote

Control".

For

external

modulation

a

voltage

of

approximately

7

volts

is

necessary

when

a

modulation

swing

of

± 200

c/s

is

required.

The

im-

pedance

of

the

external

generator

must

be

low

(approx.

1

kfl).

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",

permits

exact

frequency

selection

in

the

range

± 50 c/s

for

any

setting

on

the

main

scale.

6

By

means

of

a

noiseless

switch

on

the

front

panel,

marked

"Oscillator

Stop",

the

voltage

on

the

anode

of

the

120

kc/s

oscillator

can

be

disconnected.

This

-20

---------------------~

' MAXIMUM METER

DEFLECTION

-

301t---------

-1.0

-

501t--------

-60

1

-70

:

-80

w

<.!)

',

DISTORTED

'~SIGNAL

I

"OUTPUT

VOLTAGE"

CONTROL

~

0

>

..,:9

:::>

a..

1-

:::>

0

-

100

o .1

.2

.3

t.

.5

.6 .7 B 9

1.0

1.1

----!

0~~~~0

1.2

1.3

1.1.

1.5

VOLTS

1605+7

VOLTAGE

ON

"COMPRESSOR" INPUT

____

_.

("COMPRESSOR

VOLTAGE"

ON

MAXIMUM)

Fig.

2.

Regulation

Characteristics for

different

positions

of

the

potentiometer

marked

((Output Voltage".

7

innovation

is

specially

provided

for

reverberation

measurements.

The

same

method

is

used

for

remote

control,

the

appropriate

wiring

of

which

can

be

seen

by

referring

to

the

circuit

diagram

of

the

Oscillator.

The

output

voltage

from

the

fixed

oscillator

is

fed

to

the

grid

circuit

of

a

pentode,

tpe

grid

bias

of

which,

is

controlled,

by

means

of

a

regulating

amplifier.

To

obtain

a

higher

degree

of

control

the

working-point

of

the

pentode

is

chosen

on

the

non-linear

portion

of

the

Ia-Eg

characteristic,

near

cut-off.

The

purpose

of

this

circuit

is

to

control

automatically

the

output

power

of

the

Beat-Frequency

Oscillator

by

an

A.F.

control

voltage.

For

example,

the

voltage

from

a

standard

microphone

placed

in

the

sound

field

of

a

loud-

speaker

which

is

fed

from

the

Oscillator.

In

this

case

the

output

power

of

the

Oscillator

will

be

so

controlled

that

a

constant

sound

pressure

is

main-

tained

on

the

standard

microphone.

The

A.F.

control

voltage

should

be

fed

onto

the

screened

socket

marked

"

Compressor

Input

"

on

the

front

panel

of

the

Oscillator.

A

variable

potentio-

·

meter

,

marked

"

Compresso'r

Voltage

" is

inserted

in

the

input

circuit

of

the

regulating

amplifier

and

can

be

used

as

volume

control

for

the

output

power

from

the

Oscillator

when

automatic

regulation

is

employed.

The

regulating

amplifier

has

a

linear

frequency

characteristic

from

20

to

20ooo

c/s

and

should

have

an

input

signal

of

approximately

1

volt

on

the

grid

of

the

A.F.

amplifier

tube

for

full

regulation.

The

input

impedance,

measured

across

the

terminals

of

the

socket

marked

"

Compressor

Input"

is

approximately

100

k.Q,

and

the

maximum

obtainable

range

of

regulation

is 45

db.

The

amplified

A.F.

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

A.F.-control

voltage.

·

By

means

of

the

switch

marked

"

Compressor

Speed"

on

the

front

panel

of

the

oscillator

the

regulation

speed

can

be

varied.

Regulation

speeds

of

30-

100-300

or

1ooo

db

/sec.

may

be

chosen

by

changing

the

value

of

the

capacitor

in

the

A-C

filtering

network

for

the

rectified

control

voltage.

When

the

switch

"

Compressor

Speed"

is

in

position

"Comp

.

Off."

the

output

from

the

rectifier

is

short-circuited

thereby

disconnecting

the

automatic

regulation

circuit.

To

make

regulation

of

the

output

level

possible,

even

when

maximum

output

power

is

required

from

the

Oscillator,

the

level

of

the

high

frequency

voltage

from

the

120

kc

/s

fixed

Oscillator

is

raised

10-15

db

when

the

automatic

compression

'

is

switched

in.

The

anode-circuit

of

the

pentode

in

the

variable-It

amplifier

is

tuned

to

120

kc/s,

forming

a

band-pass

filter,

the

output

of

which

is

fed

to

the

mixer.

In

the

mixer

tube,

which

is

one

half

of

a

twin

triode,

the

120

kc

/s

voltage

is

mixed

with

the

output

voltage

from

the

variable

oscillator

.

The

frequency

of

the

variable

oscillator

can

be

altered

continuously

from

120

to

100

kc

/s

by

means

of

a

specially

designed

variable

capacitor.

This

capacitor

is

made

8

with

a

high

degree

of

accuracy

and

a

maximum

deviation

of

o.7

degrees

from

a

logarithmic

frequency

curve

is

obtained.

A

worm

gear,

connected

to

the

capacitor

spindle,

permits

automatic

tuning

with

the

aid

of

an

external

motor,

for

example

the

motor

in

the

Level

Recorder

Type

2305,

and

the

worm

gear

can

be

set

and

released

by

means

of

a

magnetic

clutch.

This

is

operated

from

a

switch

on

the

front

panel

of

the

oscillator,

or

it

can

be

operated

from

an

external

switch

or

relay.

Connection

must

then

be

made

to

the

appropriate

terminals

of

the

socket

marked

"Remote

Control"

on

the

front

panel,

and

the

control

switch

for

the

magnetic

clutch

must

be

in

position

"

Clutch

On".

By

means

of

a

pushbutton

marked

"1ooo

c/s Ref.

Signal"

an

extra

capacitor

is

introduced

in

the

tuning

circuit

of

the

variable

oscillator.

This

changes

the

frequency

of

the

oscillator

so

as

to

increase

the

output

frequency

an

amount

of

980 c/s.

With

the

scale

pointer

set

to

20 c/s

the

output

frequency

is

thus

1ooo

c/s

and

may

be

used

for

adjustment

purposes

as

explained

on

page

19,

item

17.

As

,

previously

mentioned,

the

frequency

scale

is

logarithmic

and

calibrated

20-20ooo

c/s.

When

the

capacitor

is

set

to

frequencies

above

20ooo

cis

or

below

20 c/s

the

fixed

Oscillator

is

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

fre-

quency

calibrated

paper.

The

voltage

developed

across

the

grid

circuit

of

the

variable

capacitor

is

fed

onto

the

mixer

tube

and

mixed

with

the

voltage

from

the

variable-.u

amplifier.

The mixer

tube

is

of

the

triode

type,

whereby

a

low

hum

level

is

obtained

in

spite

of

the

AC-heating

of

the

filament.

A

low-pass

filter

having

a

cut-off

frequency

of

50

kc

/s

is

inserted

in

the

anode

circuit

of

the

mixer

tube,

thus

passing

only

the

lower

frequency

obtained

by

the

frequency

conversion,

onto

the

grid

circuit

of

the

first

tube

in

the

output

amplifier

section.

Frequency

Marking.

An

arrangement,

which

can

be

operated

by

the

control

switch

for

the

magnetic

clutch,

is

the

marking

of

a

certain

frequency.

At

this

frequency

the

fixed

Oscillator

is

short-circuited,

while

at

all

other

frequencies

the

normal

output

voltage

is

available.

Basically,

the

blocking

is

effected

by

closing

a

pair

of

relay

contacts.

These

contacts

are

operated

by

a

cam

disc

which

is

mounted

concentrically

on

the

tuning

capacitor

spindle.

Normally

the

cam

rotates

with

the

spindle,

being

held

in

position

by

a

spring-loaded

friction

clutch.

However,

by

means

of

a

pawl

the

cam

disc

can

be

located

at

the

point

of

its

cycle

where

the

short

circuiting

relay

is

closed.

This

is

carried

out

by

setting

the

control

switch

for

the

magnetic

clutch

to

position

"Marking

Adjustment",

and

turning

the

capacitor

spindle

until

a

9

small

"click

l'

is

heard.

Because

of

the

friction

clutch,

it

is

now

possible

to

turn

the

capacitor

and

the

scale

pointer

relative

to,

and

independent

of

the

cam.

Release

of

the

pawl,

by

means

of

the

control

switch,

permits

the

cam

to

rotate

once

again

with

the

capacitor.

Partial

Blocking

of

Frequency

Range.

When

employing

the

special

cam

disc

OD 0065

delivered

with

the

B.F.O.,

a

part

of

th~

frequency

range

can

be

blocked,

i.e.

the

output

signal

is

inter-

rupted.

The

cam

disc

operates

the

same

relay

arrangement

as

used

for

the

frequency

marking.

The

range

length

which

can

be

blocked

corresponds

to

approximately

two

decades.

This

means

that

any

range

from

20

c/s

up

to

approximately

2ooo

c/s,

an1

from

20ooo

c/s

down

to

approximately

200 c/s

can

be

blocked

in

addition

to

the

normal

blocking

outside

the

scale

gradu-

ation.

In

Fig

. 3

is

illustrated

the

ranges

obtainable.

The

two

hatched

ranges

represent

the

blocking

ranges.

The

range

indicated

by

"Fixed"

is

the

normal

blocking

arrangement

which

functions

outside

the

scale

graduation.

The

other

range

can

be

added

to

the

normal,

as

shown

in

the

figure,

or

it

can

function

discontinued.

A

complete

instruction

of

the

mounting

of

the

cam

disc

will

be

found

under

part

Operation.

In

applications

where

the

B.F.O.

is

employed

in

conjunction

with

the

B & K

Level

Recorder,

and

where

automatic

recording

is

employed,

the

blocking

arrangement

can

also

be

used

for

remote

lifting

of

the

Level

Recorder

's

10

Frequency Marki

ng

Fig.

3.

The

two

blocking

arrangements

:

Frequency

Marking

and

Partial

Blocking

of

Frequency

Range.

writing

pen.

This

is a

great

asset

in

for

example

measurements

where

the

compressor

circuit

of

the

B.F.O. is

used.

In

this

instance

the

pen-lifting

arrangement

of

the

Level

Recorder

can

be

con~rolled

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

(20-20ooo

c/s)

of

the

B.F.O

. is

utilized,

the

normal

frequency

blocking,

which

functions

outside

the

scale

graduation,

should

be

set

out

of

pperation.

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

som-

pressor

also

at

the

initial

frequency

(20 c/

s)

is

ensured

during

the

automatic

scan.

If

the

described

method

is

not

utilized,

the

following

would

take

place:

No

signal

will

be

present

in

the

range

20ooo

c/s to

20

c/s

(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

(20 c/

s)

full

output

level

will

be

transmitted

at

20 c/s,

and

fi~st

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.

Description

of

the

Output

Amplifier

Section.

The

voltage

from

the

low-pass

filter

is

fed

to

the

control

grid

of

the

first

tube

in

the

two-stage

audio

frequency

output

amplifier

via

a

variable

potentiometer.

This

potentiometer

is

operated

by

the

knob

marked

"Output

Voltage"

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

means

of

negative

voltage

feedback,

and

the

anode

circuit

of

the

output

tube

is

coupled

to

an

auto-transformer

for

impedance

matching.

Four

different

output

impedances

are

available

and

can

be

chosen

with

the

switch

on

the

front

panel

marked

"Matching

Impedance".

The

different

positions

of

the

switch

are

indicated

by

6,

60,

600

and

6ooo

ohms

respective-

ly,

and

the

output

voltage

is

taken

from

the

terminals

marked

"Load".

It

should

be

noted

that

the

output

impedance

of

the

Oscillator

is

only

approx-

imately

10-20%

of

the

indicated

values,

but

with

correct

loading

a

max-

imum

output

power

is

obtained

with

a

minimum

harmonic

content.

Further-

more,

correct

loading

ensures

the

output

voltage

to

be

practically

independent

of

the

frequency.

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

120 ,uvolts

to

12

volts,

and

is

operated

by

the

switch

marked

"Attenu·

ator"

on

the

front

panel.

With

the

impedance

switch

in

this

position

the

output

circuit

is

connected

to

the

screened

socket

on

top

of

the

front

panel,

11

10

Ofb

0.5

c

0.2

~

:0

0.1

D

i

0.05

z

---

=Typical

Distortion

Curves

------

• Guaranteed Upper

Limit

'

0.02

~

1

~1o------------~1o~o-------------1+oo-o----------~1o~o~oo~

---Frequency

f C/s

~6~072

Fig.

4.

Distortion

curves

for

different

loads.

The

curve

marked

"Att.

10

volts"

is

obtained

from

measurements

taken

on

the

"Attenuator"

output

terminals:

open

circuit.

the

output

impedance

being

constant

and

approximately

50

ohms.

The

overall

accuracy

of

the

attenuator

is

approximately

2

%.

The

voltage

on

the

output

terminals

is

indicated

by

a

vacuum-tube

voltmeter

which

measures

the

average

value

of

the

A.F.

voltage.

It

is

calibrated

in

r.m.s.

values

of

a

sinusoidal

voltage,

and

the

accuracy

in

the

frequency

range

20-20ooo

c/s

is

1.5 %

of

full

scale

deflection.

The

sensitivity

of

the

voltmeter

is

automatically

changed

when

the

position

of

the

switch

marked

"Matching

Impedance"

is

altered

.

Full

deflection

of

the

meter

is

indicated

on

the

switch.

When

the

"Matching

Impedance"

switch

is

in

position

"Att."

the

output

voltage

available

from

the

Oscillator

will

depend

on

the

position

of

the

"Attenuator"

switch,

in

this

case

full

deflection

of

the

meter

corresponds

to

the

value

indicated

by

the

switch

position.

The

signal-to-noise

ratio

of

the

Oscillator

is

greater

than

70

db

for

maximum

output

voltage.

It

is

independent

of

the

position

of

the

attenuator,

but

some-

what

dependent

on

the

position

of

the

potentiometer

marked

"Output

Voltage".

The

best

result

is

obtained

when

this

is

positioned

on

or

around

the

point

marked

8.

Harmonic

distortion

is

dependent

on

the

setting

of

the

"Output

Voltage

Potentiometer".

The

distortion

increases

as

the

output

voltage

is

increased,

but

as

long

as

the

output

is

kept

within

the

meter

range,

the

distortion

will

be

of

the

order

indicated

in

Fig.

4.

12

Power

Supply.

The

Oscillator

can

be

operated

from

a 240, 220, 150, 127, 115

or

100

volts

AC

power

line

,

the

power

consumption

being

about

70

watts

.

The

proper

voltage

is

selectable

by

a

switch-fuse

combination

situated

at

the

rear

of

the

instrument.

To

select

the

voltage

it

is

necessary

to

firstly

remove

the

fuse

by

turning

the

hexagonal

disc

head

in

the

centre

of

the

switch

anti-clockwise

.

Then

with

the

aid

of

a

screwdriver

turn

the

head

of

the

voltage

adjuster

until

the

white

mark

is

aligned

with

the

required

voltage

.

The

fuse

is

then

replaced.

It

should

be

noted

that

if

the

apparatus

is

to

be

operated

from

a DC

power

line,

or

from

an

accumulator,

a

vibrator

unit

or

a

rotary

converter

is

required.

13

Operation

General.' ·

Firstly

ascertain

that

the

Beat

Frequency

Oscillator

is

set

to

the

appropriate

power

supply

voltage

by

means

of

the

selector

at

the

rear

of

the

instrument

and

that

the

Remote

Control

plug

on

the

front

panel

is

firmly

in

its

place.

After

connection

to

the

power

supply,

the

instrument

can

be

switched

on

by

the

toggle

switch

marked

"

Power"

on

the

front

panel.

The

dial

lights

in

the

meter

and

in

the

frequency

scale

should

immediately

come

on.

Magnetic

a~ch

~

--------

~~~

...

Corrtrol

Modulation

Frequency

Control Modulation

Swing Compressor

Speed Frequency

Scale

Adjustment

Fig. 5.

Drawing

of

the

Oscillator

1014.

14

Attenuator

Output

Load

Compressor

Input

Output

1000

r;s

Ref.

Signal

16

0590

A.

Calibration.

1.

Turn

the

toggle

switch

marked

"Power"

to

"

On"

and

allow

two

minutes

warm

up

.

2.

Set

"Modulation

Frequency"

and

"C

ompressor

Speed"

to

their

"Off"

position.

3.

Set

"Clutch,

Marking"

to

"Ma

rking

Adjustment"

position.

Rotate

the

main

scale

until

a

small

click

is

heard

and

extra

weight

is

felt

on

the

drive.

Continue

to

rotate

until

the

pointer

is

set

within

uncalibrated

portion

of

scale,

i.e.

between

20ooo

c/s

and

20 c/s.

Then

return

clutch

switch

to

"Off".

4.

Now

turn

main

scale

pointer

until

it

is

on

the

frequency

of

the

line

voltage

(e.g. 50

or

60 c/s),

checking

that

the

frequency

incremental

scale

is

on

zero.

If

not,

set

by

"Frequency

Increment"

knob

to

this

point.

5.

Set

suitable

deflection

on

the

meter

by

tuning

the

knob

marked

"Output

Voltage"

to

higher

than

center

scale

reading.

6.

Press

"Pow~r

Frequency

Beat

"

button

and

hold

to

"in"

position

and

at

the

same

time

rotate

"F

requency

Scale

Adjustment

Fine"

slowly,

until

a

large

fluctuation

registers,

slows

up,

and

practically

ceases

on

the

meter

dial.

Two

points

may

be

found

where

this

occurs,

only

one

of

which

is

correct

and

therefore

a

check

as

outlined

in

the

following

paragraph

should

be

carried

out,

firstly

releasing

the

"

Power

Frequency

Beat"

button.

7.

Turn

the

main

scale

pointer

to

20 c/s

and

with

the

"Frequency

Increment"

knob

reduce

scale

reading

to

-20

c/s

or

-30

cis

depending

upon

supply

frequency

in

use.

If

the

frequency

is

correct

the

meter

needle

will

drop

to

zero

indicating

that

the

B.F.O. is

properly

tuned.

If

it

does

not

reach

zero,

repeat

procedure

from

item

4.

8.

Finally

return

"Frequency

Increment"

to

zero.

The

B.F.O. is

ready

for

use.

N.B.

If

a

zero

point

cannot

be

found

and

is

outside

the

range

of

the

'

"Fre-

quency

Scale

Adjustment

Fine",

re-align

the

variable

capacitor

marked

)<Coarse"

with

a

screwdriver

to

give a

suitable

~etting,

which

should

occur

at

some

point

between

4

and

6

on

"Frequency

Scale

Adjustment

Fine".

B. Operation

Using

the

Output

Terminals

Marked "Load".

Apply

the

folowing

procedure:

-

1.

Set-up

and

calibrate

the

oscillator

as

described

in

A.

2.

Place

the

"Matching

Impedance"

switch

in

a

suitable

position

for

the

application.

N.B.

Full

deflection

of

the

instrument

meter

corresponds

to

the

voltage

indicated

by

the

switch

position.

3.

Connect

the

load

to

the

output

terminals

marked

"Load".

N.B.

Right

terminal

is

grounded.

15

4.

Turn

the

pointer

on

the

main

frequen

1y

dial

to

the

desired

frequency,

finely

adjusting

the

Frequency

Incren1e

nt

if

necessary.

(

For

automatic

frequency

sweep,

see

under

E).

5.

Select

a

suitable

output

voltage

by

h

rning

the

knob

marked

"Output

Voltage".

C.

Operation

Using

the

Built-in

Attenuatof

.

Apply

the

following

procedure:-

1.

Set-up

and

calibrate

the

oscillator

as

iescribed

in

A.

2.

Set

the

"

Matching

Impedance

" switcl•

in

the

position

"Att."

.

3.

Select

the

appropriate

voltage

range

IJy

means

of

"Attenuator

".

N.B.

Full

deflection

of

.

the

instrumPut

meter

corresponds

to

the

voltage

indicated

by

the

switch

position.

4.

Connect

the

load

to

the

screened

oulput

socket

on

the

top

of

the

instru-

ment

marked

"Attenuator".

5.

Proceed

as

in

B. 4

and

5.

D.

Frequency

Modulation.

When

a

frequency

modulated

output

~

:

gnal

is

required,

the

following

proce

-

dure

should

be

adopted:-

1.

Turn

the

knob

marked

"

Modula

:

ion

Frequency

" to

the

required

fre-

quency.

2.

Turn

the

knob

marked

"Modulati

.m

Swing"

to

zero.

3.

Re-calibrate

the

Oscillator

as

described

in

A.

4.

Set

the

"Modulation

Swing"

knob

to

the

required

frequency

swing

(bandwidth).

5.

Proceed

as

described

in

B

items

2

to

5,

or

C

items

2

to

5,

dependent

on

the

requirement.

E.

Automatic

Recording.

By

combining

B.F.O.

Type

1014

and

Level

Recorder

Type

2305,

or

using

Automatic

Frequency

Response

Recorder

Type

3304,

it

is

possible

to

auto-

matically

record

the

frequency

response

of

four

terminal

networks.

When

using

B.F.O.

Type

1014

and

Level

Recorder

2305,

it

is

necessary

to

connect

the

two

instruments

mecha:Qically

by

a

Flexible

Shaft

UB 0040

as

in

Fig.

6

and

to

make

the

electrical

conne

c

tions

also

shown.

Fig.

7

depicts

the

use

of

the

Automatic

Frequency

Response

Recorder

Type

3304

with

the

required

external

connections

.

For

setting-up,

calibrating

and

synchronising

the

combination

shown

in

Fig. 6

the

following

procedure

should

be

adopted

:-

1.

Ensure

power

supplies

are

correct

and

switch

powe~

toggles

to

the

"

On"

position

.

16

Object

under

test

1014

!60519

Fig.

6.

Example

of

Mechanically Connecting

the

BFO 1014 to

Level

Recorder

Type

2305.

3304

Object

under

test

!60S

SO

Fig. 7.

External

Electrical Connections

when

using

Automatic

Frequency

Response

Recorder

Type

3304.

17

2.

Calibrate

the

B.F.O.

as

described

in

A.

3.

Connect

the

instruments

as

shown

in

Fig

.

6.

Thi

s is

done

by

connecting

a

flexible

driving

cable

(UB 0040)

to

the

upper

driving

shaft

of

the

Recorder

"Drive

Shaft

I"

located

at

the

right

-

hand

side

and

to

the

front

of

the

Level

Recorder.

Taking

the

other

end

of

the

cable,

insert

and

screw

in

drive

on

left-hand

side

of

B.F.O.

(Check

engagement

by

switching

th

e

Level

Recorder

"Start

/

Stop"

switch

to

"Start"

and

the

B.F

.O.

magnetic

clutch

to

"On"

and

note

if

scale

pointer

rotates).

4.

Switching

"Paper

Drive"

to

"Stop",

continue

with

the

following

proce

-

dure

referring

Fig.

8.

Potentiometer

Range

db

Range Potentiometer

Single

Chart-

Cont. Record

Evant Marking

Drive

Shaft

n

Drive

Shaft

I

Fig.

8.

Level

Recorder

Type

2305

viewed

from

above.

5.

Load

the

Level

Recorder

with

the

desired

recording

paper.

(Follow

instructions

in

Level

Recorder

Manual).

6.

Select

and

insert

required

Range

Potentiometer

. (N.B.

Place

"

Potentio-

meter

Range

db

"

switch

to

"Standby"

when

changing

potentiometers).

7.

Switch

"

Potentiometer

Range

db

"

until

figure

corresponds

to

the

Range

Potentiometer

being

used,

i.e. "10

",

"25",

"5

0"

or

80".

8.

By

means

of

the

switch

"

Rectifier

Response",

select

R.M.S.

or

if

specially

required

one

of

the

other

three

positions

Average,

Peak,

or

D.C.

9.

Turn

the

"Lower

Limiting

Frequency"

switch

to

the

cut-off

value

(10,

20,

50

ox:

200 c/s) .

10

.

Set

"Writing

Speed"

to

required

position.

18

(Full

ex]>lanations

of

items

8, 9

and

10

can

be

obtained

from

the

Level

Recorder

·

Manual

).

Brüel & Kjær 1014 User guide

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