BRUEL & KJAER 2107 User guide
Frequency
Analyzer
Type 2107
•
i
~
•.
•
·.!:_,
~·-
-.
,. .
~
.
~
~·
=
.
•
An
Audio
Frequency
Analyzer
of
the
constant
percentage
bandwidth
type.
It
has
been
designed
especially
as a
Narrow
Band
Sound
and
Vibration
Analyzer,
but
may
be
used
for
any
kind
of
voltage
and
sound
level
measurements,
frequency
analysis,
or
distortion
measurements
within
the
range
20
-
20ooo
c/s.
The
instrument
can
be
automatically
tuned
from
an
external
motor
and
combined
with
the
B & K
Level
Recorder
for
automatic
recording
of
spectro-
grams.
Built-in
true
RMS,
arithmetic
average,
and
peak
rectifiers.
BRUEL&KJJER
Ncerum,
Denmark
.
eye
80
05
00
•
.;:;;:"
BRUKJA,
Copenhagen
• Telex:
5316
BB
2107
;
Frequency Analyzer
Type 2107
AUGUST
1962
Contents
page
Description . .
........................................
. 3
General
.......................................................
. 3
Technical
Description
..
........................
.
...............
. 4
Input
Amplifier
...............................................
. 4
Ovedoad
Indicator
.............................................
. 4
Weighting
Networks
.........
.
.......
......
....................
. 4
Selective
Amplifier
Section
.....................................
. 6
Output
Amplifier
.....
.
..........
. .
..
....
.......................
. 9
Pow
er
Supp
1
ly
.......
........
.
..................................
. 9
Reference
Voltage
............
.
.......
..
.
..
..
.. ..
.
..........
.
..
.
10
Overload
and
Clipping
......
.
..................................
.
10
Mechanical
Parts
...
...
. .
.... ....
...
................
..
...
....
..
.
11
Identification
of
Control Knobs, Terminals etc.
...........
. 12
Operation
............................................
. 16
Sensitivity
Adjustments
........
..
...
..
. .
......
.
..............
..
. .
16
Voltage
Measurements
......
.
.....
.
.......
.
..
.
.................
.
16
Frequency
Analysis
.............................................
.
17
Distortion
Measurements
..
.
...
.
.............
.....
.....
.
......
..
.
17
Sound
Level
Measurements
..........................
.
....
.
...
. . .
18
Automatic
Reco
·
rding
of
VoHage
Analysis
..
.
........
. . .
....
.
....
.
21
Rang
e
Potentiometer
Correction
...........
.
.........
...
. .
.......
.
23
·
Hecor
.din.g
Evaluation
..................
.
.......
.
...........
..
...
.
24
Automatic
Recordh1g
of
Sound
Spectra
...........................
.
24
Evaluation
of
th
e
Sound
Spectrogram
.
....
...
.
.....
. . .
....
......
.
21
Use
of
Ref
ere
nc
e
Sound
Sources
for
Calibration
.................
.
28
Applications
.........................................
.
Distortion
Measurements
.......................................
. 29
29
·~
The
Frequency
Analyzer
Type
2107
Used
as
Bdd.ge
Indicator
.
..
..
.
30
Aut
·
omatic
Narrow
Band
Frequency
Analysis
.........
...
. .
..
....
. .
31
Noise
Measurements
and
Hecordin.g .
..........
..
....
.
...........
.
33
Vibration
Measurements
.....
........
...
. .
...
.. ..
. . .
..
·. . .
.......
.
35
Measurement
of
Heverberation
Time
.............................
.
37
Sound
Insul
·
ation
Measurements
.................................
.
39
Absorption
Measurements
on
Sound
Insulating
MateriU'ls
.........
.
40
Appe·
ndix
............................................
. 42
Specificatlo·
ns
. .
.......................
_
...............
. 45
Description
G-ener
'al.
Type
2107 is
an
AC
operated
audio
frequency
analyzer
of
the
constant
percentage
bandwidth
type.
It
has
been
designed
especially
as
a
narrow
band
sound
and
vibration
analyzer,
but
may
be
used
for
any
kind
of
frequency
analysis
and
distortion
measurement
within
the
specified
frequency
range.
A
built-in
mechanical
device
enables
automatic
tuning
from
an
externaJ
"Meter
Range"
"Range
Multiplier"
¥&0f93
Fig. 1.1.
Block
diagram
of
the
Frequency
Analyzer.
motor,
e.g.
the
motor
in
one
of
the
B & K
Level
Recorders.
When
used
to-
gether
with
a
Level
Recorder
Type
2305
frequency
amplitude
diagrams
can
be
recorded
automatically
on
preprinted
frequency
calibrated
recording
paper.
The
analyzer
can
also
be
used
as
a
linear
amplifier
and
a
vacuum-tube
volt-
meter.
In
addition
it
is
supplied
with
the
weighting
networks
for
sound
level
measurements
"A",
"B"
and
"C"
the
characteristics
of
which
are
suggested
Qy
E.J.C. (
Helsinki
1961)
and
a
7-poled
input
socket
for
connection
of
a
B & K
Condenser
Microphone
or
Preamplifier
as
required.
The
instrument
is SUJ?plied
with
an
output
switch,
by
means
of
which
the
rectifier
and
meter
circuit
can
be
switched
to
measure
either
the
peak,
the
arithmetic
average
or
the
true
R.M.S.
value
of
the
input
signal.
To
enable
3
•
easy
and
accurate
meter
reading
for
both
high
and
low
frequency
signals
two
different,
standardized
meter
damping
characteristics
can
be
selected.
A
means
is
also
provided
for
connection
of
external
filters,
for
example
the
Band
Pass
Filter
Set
Type
1612
between
the
amplifier
stages.
Technical
Description.
The
Frequency
Analyzer
Type
2107
consists
of
an
input
amplifier,
a
number
of
weighting
networks,
a
selective
amplifier
section,
and
an
output
amplifier,
see
also
block
diagram
Fig.
1.1.
Input
Amplifier.
The
input
impedance
measured
at
the
"Amplifier
Input"
bushing
is
2.22
M.Q
which
is
the
total
resistance
of
the
"Meter
Range"
attenuator.
This
attenuator
consists
of
six
selected
resistors
and
four
capacitors
for
frequency
response
compensation
and
is
directly
coupled
to
the
grid
of
the
first
tube
in
the
input
amplifier.
The
amplifier
consists
of
two
low-noise,
low-microphonic
twin
triodes.
The
two
halves
of
the
first
tube
constitute
a
two-stage
RC-coupled
amplifier,
and
the
two
halves
of
the
second
tube
are
paralleled
in
a
cathode-follower
coupling.
This
paralleling,
together
with
the
great
amount
of
negative
feed-
back
ensure
an
output
impedance
at
the
"Ext.
Filter
Input"
bushing
of
less
than
10
Q.
The
gain
of
the
amplifier
measured
from
the
grid
of
the
first
tube
(at
the
"Amplifier
Input"
bushing
with
"Meter
Range"
in
position
"10 mV")
to
the
cathodes
of
the
second
tube
(at
the
"Ext.
Filter
Input"
bushing)
is 40
db
± 2
db.
The
cathodes
of
the
second
tube
are
directly
connected
to
the
"Ext.
Filter
Input",
and
to
ensure
less
than
o.1 %
distortion
of
the
output
voltage
this
should
not
exceed
1 V
r.m.s.
sine-wave
by
a
load
of
500
.Q,
or
10 V
r.m.s.
sine-wave
by
5ooo
Q.
Note:
Since
no
coupling
capacitor
is
present,
a DC
voltage
of
60-100
volt
can
be
measured
across
the
"Ext.
Filter
Input
"
terminall.
The
max.
DC
load
must
not
exceed
1 rnA.
Overload
Indicator:
The
output
of
the
input
amplifier
is
paralleled
by
an
overload
indicator.
The
indicator
is
so
designed
that
it
gives
a
visual
indica-
tion
when
signal
peak
voltages
exceed
4.5 V
on
the
output
of
the
input
amplifier.
The
signal
to
be
monitored
is
amplified
in
a
triode
connected
pentode
and
fed
to
a
gas
tube,
indicating
overload
by
a
red
light.
Refer
also
to
item
"Overload
and
Clipping"
on
page
10.
Weighting
Networks.
The
weighting
network
assembly
is
placed
on
a
"drawer"
on
the
center
chassis
of
the
apparatus.
It
is
an
L,
C,
R
network
with
five
different
outputs
corresponding
to
five
different
frequency
characteristics:
"2
-
40ooo
c/s,
4
Linear
",
"20-
40ooo
c/
s",
Curve
A,
Curve
B
and
Curve
C as
shown
in
Fig. 1.2.
The
desired
operating
characteristic
can
be
chosen
by
means
of
the
swit
ch
marked
"
Weighting
Network
".
Amplification
tab
-10
I I
l_l_l_IJI
Linear
2-
40
000
C/5
and
Linear
2-40
000 C/5
,,
I
II
V'
v
~
,.........
~--~
~
. J I n..,to.l I I
linear
I--
~
Linear
20-40000
C/5
20-40
000
C/5
~
yloo-'8
I--'
A
'~~A
]/
C+8
II
~v
"
v v II
lJ
~~
ll
yf-1-
lr'
II
-20
-30
-
40
-50
-601
10
102
10
3 2
10'
2
1os
2 5
IO'C/s
Frequency-
/61980
Fig. 1.2.
Typical
overall
frequency
characteristics
of
Type
2107.
db
l
0
10
c
.~
..
g
20
c
QJ
..
..
<(
30
/
--
~---"
/
-~
v
40
./
-"""
,....
/
-~
v
./
1--"
50 v
60
0.05
0.1
0.2
1
lA
IJ
~
l)li
~I\
1/IJI/
~\~\
vv
1)11
~\~\
1\
/
Vi/
1/1/
l\~\
\'
"
/
vv
,,,,
\~\
1\'
"
~"--r-.
20 db
v
lJ
VII
~\
[\'
1'---t--
25
dtl
I'
v
ViJ
\
1\'
"""1'---t--
30dtl
I'
vv
1\'
......
,....1"-
35db
~
-
v
/~
1"'-t-
40db
""
~
1
a
1
~lm~m(
I
0.5
1 2 5
10
20
___.
f
To
mot,f
Fig. 1.3.
Typical
selectivity
curves
of
the
Analy
zer.
The
number
of
db
marked
on
the
curves
correspond
to
the
setting
of
the
"Frequency
Analysis
Octave
Selectivity"
knob.
5
Selective
·
Amplifier
Section.
The
selective
amplifier
section
is
switched
in
by
means
of
the
"Function
Selector"
switch,
see
also
the
block
diagram
Fig.
1.1.
When
the
switch
is
in
one
of
the
positions
"Freq.
Analysis"
or
"Auto"
the
instrument
operates
as
a
narrow
band
analyzer,
which
can
be
continuously
swept
through
its
entire
frequency
range
20-20ooo
c/s.
The
frequency
characteristic
of
the
band-pass
filter
can
be
adjusted
by
the
switch
marked
"Frequency
Analysis
Octave
Selectivity".
Typical
response
curves
are
shown
in
Fig.
1.3
where
fo
is
the
center
frequency
of
the
filter
i.e.
the
frequency
to
which
the
Analyzer
is
tuned.
Around
the
"Frequency
Analysis
Octave
Selectivity"
knob
the
attenuation
in
db
of
a
frequency
one
octave
away
from
fo
is
marked.
These
selectivity
values
correspond
to
the
following
relative
bandwidths
of
the
selection
filter:
Octave
Selectivity
in db
20
25
30
35
40
max.
approx.
45
3 db
Bandwidth
in
Percent
29
21
16
12
8.5
6
which
by
means
of
the
graph
shown
in
Fig.
1.4
can
be
transferred
into
parts
of
an
octave.
Bandwidth
in
Octaves
0,5
0,4
0,3
0,2
~
~-"""""
..,.,..,..,
0,1
~
45
40
35
("Max.")
....,.,.,.
~
~
~
30
25 20
"Octave
Selectivity
db"
't-6019/f
Fig. 1.4. Curve
showing
the
correlation
between
the
setting
of
the
knob
"Octave
Selectivity
db"
and
the
filter
bandwidth
expressed
in
parts
of
octaves.
From
the
block
diagram
Fig.
1.1
it
can
be
seen
that
the
selective
amplifier
section
actually
consists
of
two
series
connected
selective
amplifiers.
The
band-pass
characteristic
of
the
Analyzer
is
obtained
by
a
frequency
rejective
6
negative
feedback.
To
stabilize
the
amplifiers
a
certain
amount
of
linear
negative
feedback
is
also
introduced
.
Each
amplifier
contains
a
cascode
coupled
twin
triode
, a "
bridge
"
tube
and
a
cathode
follower
(
one
half
of
a
twin
triode).
The
input
signal
to
the
first
amplifier
is
fed
to
the
"
upper"
half
of
the
cascode
and
the
linear
negative
feedback
is
introduced
via
the
"
bridge"
tube
to
the
cathode
of
the
"lower"
part
of
the
cascode.
The
selective
feedback
circuit
is
shown
in
Fig
.
1.5.
It
consists
of
the
"
bridge
"
tube,
a
resistance-capacitance
network
of
the
"
Wien-Bridg
e"
type
and
a
cathode
follower.
The
output
voltage
from
the
first
selective
amplifier
is
taken
from
the
plate
of
the
"bridge"
tube
and
fed
to
the
second
selective
amplifier
via
the
cathode
follower.
To
obtain
the
required
amount
of
feed-
Voutput
V
feedback
+~0195
Fig. 1.5. Basic
schematic
diagram
of
the
((
Wien-Bridge"
arrangement
used
in
the
selective
feedback
circuits
of
the
Frequency
Analyzer
Type
2107.
back,
the
feedback
voltage,
Vf e
edb
ac
k
developed
in
the
Wien
Bridge
is
fed
to
the
grid
of
the
"lower"
.
part
of
the
cascode.
The
extensive
use
of
cathode
followers
in
the
selective
amplifiers
has
been
necessary
to
ensure
correct
impedance
matching
in
the
circuit.
7
of
the
cascade.
The
extensive
use
of
cathode
followers
in
the
selective
ampli-
fiers
has
been
necessary
to
ensure
correct
impedance
matching
in
the
circuit.
The
Wien
Bridge
consists
of
two
pure
resistors
(R
and
2R)
and
two
arms
containing
a
series
RC
network
and
a
parallel
RC
network
respectively,
Although
the
DC
supply
for
the
"bridge"
tube
is
inserted
between
the
pure
resistors,
the
bridge
acts
as
a
closed
bridge
with
regard
to AC,
because
of
the
200
p,F
capacitor
(Ce). At a
certain
frequency
fo
=
--
1-
the
feedbacl<
2n
RC
voltage,
(V
feedback),
is
zero,
and
consequently
the
gain
of
the
selective
ampli-
fier
section
maximum.
At
other
frequencies
the
feedback
voltage
,
(V
fe
e
dback)
,
is
great.
In
this
way
the
desired
selective
frequency
characteristic
of
the
Analyzer
is
obtained.
The
second
selective
amplifier
is
identical
to
the
one
just
described.
If
now
the
Wien
Bridge
was
connected
in
series
with
the
amplifier
instead
of
in
the
feedback
loop
the
resulting
frequency
characteristic
of
the
Analyzer
would
be
exactly
inverted,
i.e.
it
would
reject
the
frequency
to
which
it
was
tuned.
This
is a
desirable
feature
when
for
instance
distortion
measure-
+10
db
0
-10
-20
-30
-40
-50
-60
-70
...........
/
I
0~
0.2
0.5
2 5
---.-~a
Fig. 1.6.
Typical
frequency
rejection
curve.
10
/6{093
ments
are
undertaken.
The
"Function
Selector
"
switch
includes
for
this
reason
a
position
marked
"Freq.
Rejection.
When
the
switch
is
in
the
"Freq.
Rejection
"
position
the
final
of
the
two
series
connected
selective
ampli-
fiers
is
coupled
as
a
linear
amplifier
with
a 30
db
gain.
The
first
selective
amplifier
is
switched
so
that
tlie
"Wien-Bridge"
is
connected
in
series
with
the
amplifier,
whereby
the
selective
circuit
acts
as
a
rejection
circuit,
(see
Fig. 1.1). A
small
amount
of
selective
negative
feedback
is
still
main-
tained,
which
is
necessary
to
ensure
that
the
rejection
curve
is
not
more
than
o.5
db
down
at
the
2nd
harmonic
to
the
tuned-in
frequency.
To
ensure
perfect
balance
of
the
"Wien-Bridge"
an
additional
potentiometer,
"Fre-
quency
Rejection
Balance",
is
introduced
in
one
of
the
bridge
arms.
By
means
of
this
potentiometer
the
bridge
circuit
can
be
brought
in
balance
for
any
po
s
ition
of
the
frequency
scale
pointer.
An
attenuation
of
70
db
at
the
tuned-in
frequency
is
obtainable,
see
Fig.
1.6.
To
ensure
correct
gain
of
the
Analyzer
for
all
settings
of
the
"Function
Selector"
switch
two
screwdriver
operated
gain
adjustment
potehtiometer
s
are
pr
_
qvided.
They
adjust
the
gain
of
the
selective
amplifier
section
and
are
placed
on
the
back
of
the
instrument.
One
of
th
em is
marked
"
Freq.
Rejection
-
Level
Adjustment",
and
the
other
"
Frequency
Analysis
-
Level
Adjustment"
.
Output Amplifier.
The
signal
from
the
selective
amplifier
section
is
fed
to
the
output
amplifier
via
the
"
Range
Multiplier"
switch.
The
input
impedance
of
the
output
amplifier
is
1.46 MD
as
measured
on
the
"Ext.
Filter
Output"
bushing.
The
"Range
Multiplier"
attenuator
consists
of
five
selected
resistors
with
a
ratio
of
10
db
between
two
consecutive
switch
positions,
and
a
trimmer
capacitor
for
frequency
characteristic
compensation.
The
output
amplifier
is a
three-stage
R-C
coupled
amplifier
with
negative
feedback.
The
feedback
can
be
adjusted
by
means
of
the
two
screwdriver-
operated
potentiometers,
which
are
accessible
through
holes
in
the
front
plate
of
the
instrument
and
marked
"Sensitivity-Condenser
Microphone"
and
"Sensitivity-Amplifier
Input".
The
adjustment
range
of
the
potentiometers
is
approximately
6
db.
To
ensure
a
low
output
impedance
(less
than
50
Q)
at
the
"
Recorder"
output
bushing
the
output
stage
consists
of
a
cathode
follower.
In
addition
capacitive
feedback
is
accomplished
through
an
adjustable
bushing
capacitor.
This
is
done
to
reduce
the
input
capacity
of
the
output
amplifier
to
a
minimum,
whereby
the
frequency
response
of
the
amplifier
is
less
dependent
on
the
setting
of
the
"Range
Multiplier"
switch.
*)
To
the
output
cathode
follower
is
also
coupled
the
meter
circuit.
This
.
circuit
consists
of
diodes
and
resistors
and
gives
the
meter
rectifier
. a
characteristic
which
ensures
true
RMS
rectification
for
any
signal
with
a
crest
factor
of
five
or
les~
:
**)
A
switch
in
the
re
c
tifier
circuit
also
enables
the
arithmetic
average
and
the
peak
(
half
the
peak-to-peak
)
value
of
the
input
signal
to
be
measured
.
The
meter
itself
is a
moving
coil
instrument
with
a
maximum
current
consumption
of
o.2 rnA.
It
satisfies
the
dynamic
requirements
for
precision
sound
level
meters
as
suggested
by
I.E
.C. (
Helsinki
1961).
Power
Supply.
The
power
transformer
is
fused
on
the
primary
side.
The
secondary
side
consists
of
four
separate
windings,
one
for
the
plate
voltage
supply,
one
*)
For
more
detailed
information
see
page
6-7, B & K
Technical
·Review No. 3
July
1958
.
*
*)
For
more
detailed
information
on
this
circuit
see B & K
Technical
Review, No. R July
1958.
9
for
the
voltage
supply
to
the
condenser
microphone
bushing,
and
two
for
the
filament
voltage
supply.
DC
heating
and
special
compensation
arrange-
ments
have
been
employed
on
critical
tubes
circuits
to
decrease
the
hum
level.
To
facilitate
the
use
of
condenser
microphones
requiring
differ
.
ent
polarization
voltages
the
polarization
voltage
supply
for
the
microphone
is
made
adjust-
able
by
means
of
a
screwdriver-operated
potentiometer
located
on
the
back
of
the
instrument
and
marked
"Polarization
Voltage".
The
adjustable
voltage
range
is
150
volts
to
250
volts.
Reference
Voltage.
The
reference
voltage
is a 6.3 mV RMS
zener-diode
stabilized
square-wave
.,
signal
of
the
mains
frequency.
When
the
Analyzer
is
s~itched
for
frequency
analysis
("Function
Selector"
in
position
"Freq.
Analysis"
or
"Auto")
and
turned
to
the
frequency
of
the
mains,
only
the
fundamental
of
the
square-wave
reference
signal
is
measured
on
the
instrument
meter.
An
adequate
reference
voltage
correction
is
in
this
case
automatically
accomplished.
Overload
and
Clipping.
Care
must
be
taken
not
to
overdrive
the
input
amplifier.
By
using
the
Analyzer
in
the
nonselective
condition
overdriving
of
the
amplifier
sections
can
be
observed
on
the
indicating
meter
deflection
i.e.
within
full
deflection
th
ere
is
no
overload,
provided
the
signal
crest
factor
is
below
4.5.
In
the
selective
condition,
overdriving
of
the
output
amplifier
only
can
be
observed
on
the
indicating
meter
as
signal
components
outside
the
pass-band
of
the
filter
or
weighting
network
inserted
are
attenuated.
To
obtain
an
overload
indication
for
th
e
input
amplifier
a
visual
indicator
is
connec
t
ed
in
parallel
to
the
output
of
the
input
amplifier,
as
previous~y
described
.
The
indicator
lights
up
when
signal
peak
voltages
on
this
point
exceeds
4.5
volts
(3.HJ''V
r.m.s.
sine-wave)
i.e. 10
db
higher
than
the
1 V
r.m.s.
sine-wave,
as
stated
for
o.1 %
nonlinear
distortion.
The
4.5
volts
peak
voltage
indication
li~nits
the
measurement
s
to
signals
with
crest
factor
fc
lower
than
4.5,
which
also
is
the
highest
crest
factor
allowable
at
full
r.m.s.
drive.
The
higher
peaks
in
the
signal
have
to
contain
a
certain
energy
to
be
indicated
.
When
for
example
measurements
a,re
made
on
noise
signals
with
Gaussian
distribution
the
indicator
will
only
react
for
noise
peaks,
which
are
lower
than
approx-
imately
2.5
times
the
r.m.s.
value,
i.e. fc
lower
than
2.5.
To
be
able
to
check
on
how
far
the
input
amplifier
is
driven
in
making
selective
measurements,
the
"Fu;1ction
Selector
"
of
the
Analyzer
should
first
be
set
to
position
"Se
lective
Section
off
"
and
"
Range
Multip
li
er"
on
"0
db
,
x 1".
The
·'r.m.s.
average
or
peak
drive
of
the
amplifier
can
then
be
read
on
the
indicating
meter
.
Full
deflcciivn
corresponds
to
1
volt
on
the
ou
tput
of
10
•
•
the
input
amplifier.
From
the
above
can
be
seen,
that
in
selective
measure-
ments,
when
the
input
amplifier
is
driven
to
maximum
,
the
sensitivity
of
the
Analyzer
can
only
be
increased
by
"
Range
Multiplier"
.
1\fechanical Parts.
The
continuously
frequency
scan
of
the
Analyzer
can
be
done
manually
as
well
as
remotely.
For
remote
operation
the
scanning
is
attained
via
a
worm
gear
with
ratio
25 : 1
from
an
external
drive,
for
example
one
of
the
B & K
Level
Recorders.
A
magnetic
clutch
arrangement
permits
the
set
and
release
of
the
automatic
drive.
The
clutch
is DC
operated
by
a 600 Q
coil
with
an
operating
voltage
of
20
volts.
By
means
of
a
set
of
toothed
wheels
the
scanning
mechanism
is
connected
to
the
"Frequency
Range"
switch
switch-
ing
this
automatically
once
per
completed
turn
of
the
scale
pointer,
i.e.
each
time
one
of
the
six
frequency
ranges
are
scanned.
11
Identification
of
Control Knobs, Terminals etc.
Overload lndic dicating Meter
Polarization Volt
~-----
Power
.
,.---
- - Meter Switch
Range
Multi
plier
Sensitivity
Amplifier Input
Frequency Rejection
Balance
Frequency Range
Frequency Tuning Function Selector
Frequency Analysis
Octave Sensitivity
46019,?
Fig. 2
.1
.
Frequency
Ana
ly
zer
Type
2107
with
control
knob
identification.
identification.
Front
Plate.
12
Overload
Indicator:
Indicates
for
peak
voltages
higher
than
4,5
V,
i.e.
10
db
above
1 V
r.m
.s.,
on
the
output
of
the
input
amplifier
.
"Polarization
Voltage":
"Condenser
Microphone":
For
measuring
of
the
microphone
polarization
voltage.
A
DC
voltmeter
with
an
internal
resistance
of
at
least
20ooo
ohm
/
volt
sho
uld
be
connected
between
this
terminal
and
ground
(c
hassis
).
Input
terminal
for
the
B & K
Condenser
Micro-
phones
(
Cathode
Followers
)
and
Preamplifiers
.
•
•
"Input
Potentiometer":
'"Input Switch":
"Sensitivity,
Condenser
Microphone":
For
continuous
attenuation
of
input
signal.
Selection
of
one
of
the
three
input
facilities
"Input
Potentiometer",
to
be
used
for
relative
measurements.
"Direct".
The
signal
is
applied
direct
from
the
"Amplifier
Input"
to
the
attenuator
"Meter
Range".
"
Condenser
Microphone".
Screwdriver
operated
potentiometer,
for
adjustment
of
sensitivity,
when
input
"Condenser
Microphone"
is
used.
"Amplifier Input":
The
signal
is
applied
to
the
attenuator
"Meter
Range"
either
direct
or
via
the
"Input
Potentio-
meter",
depends
on
position
of
"Input
Switch".
"External
Filter
Input":
"\\
7
eighting
Network":
Intended
for
connection
of
external
filter
input,
parallels
the
output
of
the
input
amplifier.
Note:
A DC
voltage
of
approximately
75
volts
is
present.
Do
not
drain
mbre
than
1 rnA d.c.
"
Curve
A",
"B"
or
"C"
is
switched
in.
Connected
in
cascade
with
the
selective
ampli-
fier
section
when
"Function
Selector"
is
set
to
position
"Freq.
Rejection",
"Freq.
Analysis"
or
"Auto".
"Linear,
20-40ooo"
c/s, a
network
is
switched
in
cutting
of
below
20
c/s
with
a
maximum
slope
of
18
db
/
octave.
"Linear,
2-40ooo"
c/s
the
Analyzer
is
switched
as
linear
amplifier,
when
the
"Function
Selector"
is
set
to
position
"Selective
Section
off".
"Ext.
Filter".
External
filter
connected
to
"External
Filter
Input"
and
"External
Filter
Output"
is
switched
in.
"Frequency
Range":
For
selection
of
the
six
frequency
ranges.
"Frequency
Tuning":
For
setting
of
frequency
within
the
ranges
of
"Frequency
Range"
for
analysis
and
rejection.
13
14
"Power":
"Metel"
Switch":
"Meter Range":
"Recorder":
"Range
Multiplier":
"Sensitivity,
Amplifier Input":
"External
Filter
Output":
"Frequency
For
switching
off
and
on
the
power
for
the
apparatus.
For
selection
of
the
three
different
meter
indicating
properties
"Average"
"Peak"
(half
peak-to-peak)
"R.M.S."
The
three
positions
("
Fast")
to
the
left
gives
the
smallest
damping
of
the
indicating
meter
deflec-
tion.
·
The
positions
("Slow")
to
the
right
give
the
highest
damping
.
In
the
middle
position
"Off",
the
meter
circuit
is
disconnected.
Step
attenuator,
20
db,
for
attenuation
of
input
signal.
Output
terminal.
Step
attenuator,
10
db.
Inserted
between
selective
amplifier
section
and
output
amplifier.
Screwdriver
operated
potentiometer
for
adjustment
of
sensitivity
when
terminal
"Amplifier
Input"
is
used.
Intended
for
connection
of
the
output
of
an
exter
-
nal
filter.
Is
switched
in
circuit
with
the
input
of
the
selective
amplifier
section
when
"Weighting
Network"
is
set
to
"Ext.
Filter"
position
.
Rejection Balance":
To
obtain
maximum
rejection
of
a
signal
selected
on
the
Frequency
Tuning
scale,
with
the
"Function
Selector"
set
in
the
"Freq.
Rejection"
position.
"Frequency
Analysis
Octave Selectivity":
To
select
six
different
degrees
of
selectivity
(
band-
with)
of
the
band-pass
filter
when
"Function
Selector"
is
set
to
the
"Analysis"
or
"Auto"
posi-
tion.
"Function
Selector":
"Freq.
Rejection".
Any
signal
of
a
distinct
fre-
quency
selected
on
the
Frequency
Tuning
scale,
can
be
rejected.
Maximum
attenuation
is
attained
by
adjusting
the
"Frequency
Re-
jection
Balance".
"Selective
Section
off".
The
selective
amplifier
section
is
switched
out
of
circuit,
i.e.
the
fre-
quency
response
of
the
Analyzer
is
solely
determined
by
the
position
of
the
"
Weighting
Network"
switch.
"Freq.
Analysis".
The
Analyzer
is
set
for
analysis
of
signals
the
frequency
of
which
are
selected
on
the
Frequency
Tuning
scale.
Six
different
bandwidths
can
be
chosen
by
the
"Frequency
Analysis,
Octave
Selectivity"
switch.
"A
uto
".
Same
data
as
obtained
in
the
"Frequency
Analysis"
position
but
an
electromagnetic
clutch
is
operated
,
clutching
in
the
remotely
controlable
and
mechanic
frequency
scanning
arrangement.
Rear
of
Instrument.
(Refer
Fig.
2.2)
Mains
Voltage
Selector
and
Fuse
Holder
·:
Adjustment
Potentiometers:
For
factory
adjustment
only
Frequency Analysis-
Level
Adjustment
(P15)
Frequency Rejection-
Level
Adjustment
(P14)
The
fuse
should
be
of
1.5
amp.
(medium
lag
).
Screwdriver
operated
potentiometers
accessible
through
the
perforation
of
the
rear
plate.
The
potentiometers
identified
by
"For
factory
adjust-
ment
only"
should
not
be
adjusted
unless
a
factory
adjustment
of
the
Analyzer
is
carried
out.
For
adjustment
of
the
remaining
potentiometers,
refer
to
part
Operation.
Mains
voltage selector
===--------=__,
------
---- and fuse holder
~,,~,,
~
-
LQJ~
------------
~~
Polarisation
Voltage
(
P4)
'------------------J
I6Noo
Fig. 2.2.
Rear
view
of
Frequency
Analyzer
Type
2107.
15
Operation
Sensitivity Adjustments
1.
Check
that
the
instrument
is
set
to
the
correct
power
and
allow
a
few
minutes
to
warm-up.
2.
Set
the
knobs
listed
in
the
following
positions:
-
"Direct"
voltage.
Switch
on
"Input
Switch"
to
"Weighting
Network"
to
"Frequency
Range"
"Function
Selector"
"Frequency
Analysi~
Octave
Selectivity"
"Range
Multiplier"
"Meter
Switch"
to
to
"2-4
0ooo
Linear
"
"20-63"
to
to
to
"Selective
Section
off"
"20
db"
"X
1
(0
db}"
"Fast,
RMS"
"Meter
Range"
to
"Ref.'
3.
Adjust
the
"Sensitivity
Amplifier
Input"
until
a
meter
deflection
to
the
red
mark
on
the
meter
scale
is
obtained.
4.
Set
Input
Switch
to
"Condenser
Microphone".
5.
Adjust
the
"Sensitivity
Condenser
Microphone"
until
a
deflection
to
the
red
mark
on
the
meter
scale
is
obtained.
6.
Set
"Input
Switch"
to
"Direct"
"Function
Selector"
to
"Freq.
Analysis"
and
turn
the
frequency
scale
to
the
mains
frequency.
7.
If
a
meter
deflection
is
not
obtained
to
the
red
mark
on
the
scale
adjust
the
potentiometer
marked
"Frequency
Analysis
-
Level
Adjustment"
at
the
rear
.
of
the
instrument
(Fig. 2.2)
until
this
is
achieved.
8.
Set
"Frequency
Range"
to
"200-630''
"Function
Selector"
to
"Freq.
Rejection"
9.
If
a
meter
deflection
is
again
not
immediately
obtained
to
the
red
mark
on
the
scale,
adjust
the
potentiometer
marked
"Freq.
Rejection
Level
Adjustment"
on
the
back
of
the
instrument
until
accomplished.
Voltage Measurements.
To
use
the
Analyzer
as
a
normal
VTVM
apply
the
followi~g
procedure:
l.
Check
the
sensitivity
of
the
Analyzer.
See
"Sensitivity
Adjustment"
item
through
3.
16
I
•
2.
Adjust
the
"Meter
Range"
and
"Range
Multiplier"
switches
until
a
suitable
meter
deflection
is
obtained
(between
3
and
10
on
upper
volt
scale)
when
the
signal
to
be
·
analyzed
is
fed
to
the
"Amplifier
Input"
of
the
Analyzer.
(The
"Range
Multiplier"
switch
should,
when
possible,
be
in
either
of
the
two
positions
"X
1
(0
db)"
or
"X
o.3 (- 10
db)").
3.
Read
off
the
meter.
Full
scale
sensitivity
is
equal
to
the
~'Meter
Range"
indication
(V
or
m
V)
multiplied
by
the
factor
indicated
by
the
position
of
the
"Range
Multiplier"
switch.
Frequency
Analysis.
Selective
measurements
can
be
carried
out
in
the
frequency
range
from
20 c/s
to
20ooo
cis.
To
adjust
the
Analyzer
for
measurement
apply
the
following
procedure:
1.
Check
the
sensitivity
adjustment.
See
"Sensitivity
Adjustment"
page
11.
2.
Set
the
"Input
Switch"
to
"Condenser
Microphone"
if
the
"Condenser
Microphone"
input
is
used.
To
"Direct"
if
the
"Amplifier
Input"
is
used
for
absolute
measurements,
and
to
"Input
Potentiometer"
if
the
"Ampli-
fier
Input"
is
used
for
relative
measurements.
3.
Set
the
"Weighting
Network"
switch
to
"Linear,
20-40ooo"
if
normal
frequency
analyses
is
wanted.
to
"Curve
A",
"Curve
B"
or
"Curve
C"
if
a
frequency
weighted
analysis
is
desired,
see
also
Fig.
1.2.
4.
Set
the
"Frequency
Range"
switch
to
the
frequency
range
of
interest.
5.
Set
the
"Function
Selector"
to
"Selective
Section
off".
6.
Set
the
"Frequency
Analysis
Octave
Selectivity"
to
the
desired
selectivity
.
7.
Set
"Range
Multiplier"
to
"X
1 (0
db)".
8.
If
not
otherwise
required
set
"Meter
Switch"
to
"Fast,
RMS".
9.
Adjust
the
"Meter
Range"
and
"Range
Multiplier"
switches
until
a
suitable
meter
deflection
is
obtained
(between
3
and
10
on
upper
volt
scale)
when
the
signal
to
be
analyzed
is
fed
to
the
input
of
the
Analyzer.
(The
"Range
Multiplier"
switch
should
when
possible
be
in
either
of
the
two
positions
"X
1 (0
db)"
or
"X
o.3
(-10
db)").
10.
S~itch
fpe
"Function
Selector"
switch
to
"Frequency
Analysis".
11.
Turn
--
t.h
'e
frequency
scale
pointer
to
the
frequency
to
be
examined
and
read
meter.
If
the
meter
reading
is
below
3
on
the
upper
volt
scale
turn
the
"Range
Multiplier"
switch
(not
the
"Meter
Range"
switch)
counter-
clockwise
until
a
suitable
meter
deflection
is
obtained.
12.
Turn
the
frequency
scale
pointer
to
measure
other
frequencies
of
interest
and
switch
"Frequency
Range"
if
required.
Distortion
Measurements.
The
measurement
of
distortion
can
be
carried
out
by
measuring
the
harmonics
individually.
To
do
this,
apply
the
procedure
outlined
under
"Frequency
Analysis"
above.
If
it
is
desired
to
directly
measure
t~e
distortion
factor,
apply
the
following
procedure:
17
1.
Check
the
sensitivity
adjustment.
See
"Sensitivity
Adjustment"
page
11.
2.
Set
the
"Input
Switch"
to
"Input
Potentiometer",
and
apply
the
signal
to
be
measured
to
the
"Amplifier
Input".
3.
Turn
"Input
Potentiometer"
fully
clockwise.
4.
Set
the
"Weighting
Network"
switch
to
,
"20-40ooo".
5.
Set
the
"Frequency
Range"
two
ranges
away
from
the
frequency
range
which
contains
the
fundamental
frequency
of
the
input
signal.
6.
Set
the
"Function
Selector"
to
"Freq.
Rejection
".
7.
Set
the
'"'Range
Multiplier
to
"X
1
(0
db)".
8.
Set
the
"Meter
Switch"
to
"Fast,
RMS".
9.
Adjust
the
"Meter
Range"
and
"Range
Multiplier"
switches
until
a
suit-
able
meter
deflectior\. is
obtained
(between
3
and
10
on
upper
volt
scale
')
when
the
signal
to
be
analyzed
is
fed
to
the
input
of
the
Analyzer.
(The
"Range
Multiplier"
switch
should,
when
possible,
be
in
either
of
the
two
positions
" X 1
(0
db)"
or
"X
o.3
(-10
db)").
10.
Turn
the
"Range
Multiplier"
one
step
counterclockwise
and
the
"Input
Potentiometer"
counterclockwise
until
full
scale
deflection
is
obtained
on
the
meter.
11.
Set
"Frequency
Range"
to
the
range
containing
the
fundamental
fre-
quency
of
the
input
signal,
and
turn
the
frequency
dial
of
the
Analyzer
to
this
frequency
(minimum
deflection
on
the
meter).
By
means
of
the
"Frequency
Rejection
Balance",
fine
adjustment
to
minimum
meter
de-
flection
should
be
carried
out.
The
reading
on
the
meter
is
now
the
distortion
factor
with
"10"
on
the
"
upper"
volt
scale
corresponding
to
100
%,
"9"
to
90
%,
"8"
to
80 % etc.
If
a
~eflection
below
"
3"
on
this
volt
scale
is
obtained
,
turn
the
Range
Multiplier"
one
position
counterclockwise.
The
distortion
factor
is
then
read
in
percent
on
the
"lower"
volt
scale
with
"30"
corresponding
to
30 %,
"20
to
20 % etc.
If
a
meter
reading
smaller
than
"10"
on
the
lower
volt
scale
is
obtained
,
turn
the
"Range
Multiplier"
further
counterclockwis~
by
one
position.
The
upper
volt
scale
"10"
now
corresponds
to
10
%,
"9'
;
to
9%
etc.
Sound
Level
Measurements.
To
carry
out
accurate
sound
level
measurements
the
sensitivity
of
the
micro-
phone
must
be
known.
When
the
Analyzer
is
used
with
a
microphone
con-
nected
to
the
"Amplifier
Input",
the
meter
reading
is
in
volts
and
the
sound
level
must
be
calculated
on
the
basis
of
the
microphone
sensitivity.
When
the
Analyzer
is
used
wi
,fh
the
Briiel
& Kjrer
Condenser
Microphones
Type
4131
or
4~32,
however,
the
meter
reading
can
be
read
directly
in
db
SL
(decibel
so~nd
level).
To
do
so
apply
the
fbllowing
procedure:
-
1.
Check
that
the
polarization
voltage
is
correct.
The
polarization
voltage
can
~e
measured
between
the
bushing
marked
"
Polarization
Vo<ltage"
and
grou~d
and
is
adjusted
by
means
of
a
screwdriver-operated
potentiometer
18
•
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