BRUEL & KJAER 1022 - Page 12

BRUEL & KJAER 1022

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The

cut-off

section

can

be

made

wider

by

adjusting

the

cam

discs,

connected

to

the

rear

end

of

the

capaoitor

spindle.

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

exa

1

rnple

measurements

where

the

compres

,

sor

circuit

of

the

B.F.O.

is

used.

In

this

instance

the

pen-lifting

arrangement

of

the

Le

~

vel

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

(20-20ooo

c/s)

of

the

B.F.O.

i's

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

intere

~

st

and

a

proper

working

of

the

com-

pressor

also

at

the

initial

frequency

(20 c/

s)

i

~

s

ensured

during

the

a~tomaHc

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

ins

,

ide

the

scale

graduation

(20 c/

s)

full

output

level

will

be

transmHted

at

20

c/s,

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.

Description

of

the

Output

Amplifier

Section.

The

voltage

from

the

low-pass

filter

is

fed

to

the

control

grid

of

the

f~rst

tube

in

the

two-stage

audio

frequency

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

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

i,s

only

approx-

imately

10-20%

of

the

indicated

value

's,

but

when

loading

with

impedances

as

marked,

a

maximum

output

power

is

obtained

with

a

minimum

harmonic

oontent.

Furtherm10re,

correct

loading

ensures

the

output

voltage

to

be

practically

independent

of

the

frequency.

10