Brüel & Kjær 2107 User guide

,
Frequency Analyzer Type 2107
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
vo ltage and sound level measurements, frequency
analysis, or distortion measurements within the
range 20-20000 Hz.
The instrument can be automatically tuned from
an ex ternal motor and combined with the B & K
Level Recorder for automatic recording of spectro-
grams. Built-in true RMS, arithmetic average, and
peak rectifiers.
. :.~ . ";-"
BnUEL & KJN..R
NII!rum. Denmark 12' 8005 00 . $ BRUKJA . Copenhagen . relex: 5316
BS 2107
"

Frequency Analyzer
Type 2107
Reprint June 1967

Contents
page
Description .. ... . . ..... . .... . ...... .. . .. .............. 3
General .. ... . . ..... . .. . . . ................... .... . .. ...... ..... . 3
Technical Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
Input Amplifier . . , ... . , .. . .. ..... ... . ... ..... .... . ......... . .. . 4
Overload
Indicator .... ..... ................... . .... . ... . . . .... .. 4
Weighting Networks .. '.. . .... . ........ . . ..... ............ .. .... 4
Selective
Amplifier Section ...... ..... . ......... ...... ... ........ 6
Output Amplifier .................... . ............... ............ 9
Power Sup 'ply ................. . ... . .. .... .... .. .... ....... ...... 9
Reference Voltag e . .... . .... ... ..... . . .. ............ . . . . . ...... 10
Overload and Clipping ...................................... .... 10
Mechanical Parts . . . . . . . . .. . . . . . . . . .. . . . . . . . . . . .. . . . . . . . . . . . . . .. 11
Identification of Control Knobs, Terminals etc. . . . . . . . . . . .. 12
Operation ...... . .. .. ......... . ...... ". . . . . . . . . . . . . . . .. 17
Sensitivity Adjustments ... .............. . .... .. . ... ...... ... .. ... 17
Voltage Measurements .......................... . .............. . 17
Frequency Analysis ....... .. ............... '. .... .......... . .. . 18
Distortion Measurements .............. . ..... . ................... 18
Sound Level Measurements . . .......... .. ... '..... . . .. .. .. . ...... 19
Automatic Recording of Voltage Analysis ... ,............. . ...... 22
Range Potentiometer Correction ... . ... . ........ ... ...... . .. .. .. 24
Recording Evaluation ................... ... .. ...... . ... . .... . . . 25
Automatic Recording of Sound Spectra . ..... . . ... ............... 25
Evaluation of the Sound Spectrogr am ............ .... ........ . ... 28
Use of Reference Sound Sources for Calibration . .. .. .. . .. ........ 29
Synchronization with Bandpass Filt er Set ..... . ... .. ........ . .... 30
ACCesSOl'ies .. .... ..... .. ........ .. .. .. . .. ... .......... 31
Combined Units .... . ... ......... .......... . ... ........ 40
Applications
... .... . ..... . ... . .... .. ...... . .......... . 44
Distortion Measurements ........................................ 44
The Fr e quen cy Analyzer Type 2107 Used as Bridge Indi ca tor . . . . .. 45
Autom atic Narrow Ba nd Frequency Analysis ................ .. .. 46
Noise
Measurements and Hecording .. ..... ............. . .... .... . 48
Vibr a tion Me as urements . .. . .. ... ... ..... ....................... 50
Measur e ment of Reverb era tion Time ........ ... .. .. . . ........... 52
Sound Insulation Measurements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 54
Absorption M eas urements on Sound Insul a ting Materials . ......... 55
Statistical
Distribution Ana lysis .. ... .. ................... .. . ... .. 57
Appendix . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 59
Specifications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 62

Description
General.
Type 2107 is an AC operated audio frequency analyzer of the constant
percentag e 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 exte ·rnaJ
Frequency
,Rejection
~ ~\~ ~'~~e~u~~ __ l~~~i; _-:, \,
\~,-r __ Q£lsl.Y~ 'stJ.ftl:ti'dt:t._\ \ "
\ \, \
\ \ \ \
\ \ \ \ \ \
---..j.
" Meter Range"
Average
"Re corder "
"Range MuLtiplier"
Fig. 1.1. Block diagram 0/ the Frequency Analyzer.
Selective
Amplifier
.&0'93
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
m
eas urem en ts "A", "B" and "C" the cha ract er istics of whi ch are reco m·
mended in the IEC Publication 179 and a 7 -pin input socket for connection
of a B & K Conde nser Microphone or Pr ea mplifier as required.
The instrument is supplied with an output switch, by means of which the
rectifier and meter circuit can be switched to measure either the peak, the
ar ithm e tic average or th e true RMS value of the input s ignal. 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 resistance at the AMPLIFIER INPUT socket is 2.22 MQ 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 ensures an output impedance at the EXT. FILTER INPUT socket of less
than 10 Q. The gain of the amplifier measured from the grid of the first
tube (at the AMPLIFIER INPUT socket with METER RANGE in position
"10 mV") to the cathodes of the second tube (at the EXT. FILTER INPUT
socket) is 40 dB ± 2 dB. The cathodes of the second tube are directly con-
nected to the EXT . FILTER INPUT, and to ensure less than 0.1 % distortion
of the output voltage this should not exceed 1 V RMS sine-wave with a load
of 500 Q, or 10 V RMS sine-wave with 5000 £2.
Note: Since no coupling capacitor is present, a DC voltage of 60-100 volt can
be measured across
the EXT. FILTER INPUT terminals. The max. DC load
must not exceed 1 mAo
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 an RC network with five different outputs
corresponding to five different frequency characteristics: " 2--40000 Hz,
4

Linear", "20 - 40000 Hz" , Curve A, Curve B and Curve C as shown in Fig . 1.2.
The desired operating characteristic can be chosen by means of the switch
marked WEIGHTING NETWORK.
Amplification
rob
- 10
Linear 2- ~ 0 I ddJ l c/S
''''Lineo~ JI
!-"'"
20-.0000 ctS
C
-20 V
I V
,
- 30
- 40
-so
,.
-
- 60
1 5
10
1--'''''
i--"
""
10" B
VA
I
JOZ 2 5 10 ' 2
linear 2- 40 000 CIS and
~
.1 "T" FI"J r
~ L,near 20- .0000 CIS
C.B
',~A
5 10' 2 10' 2
Frequency -/61990
Fig. 1.2. Typical overall frequency characteristics of Type 2107.
dB
c
o
.....
g 20
c
QJ
.....
.....
« 30
40
50
60
0.05 0.1
-
l
~
~'
I
\\\\
II
\\
1\
/'
V
VI
\\
1\
"-
,.-
V
II
\\
"-
"-
......
/
,.-
/
01
\\
\"
"-
/
.....-
.,//
II
\
1\'
"-
-
//
1\
"-
./
-/
>- ......
...-/
~Iol~:m~m(
0.2
0.5
2
-.... f
To
5
20 dB
25dB
30dB
35 dE
40 dB
10 20
MO.,
Fig. 1.3. Typical selectivity curves of the Analyzer. The number of dB marked
on the curves correspond to the setting of the FREQUENCY ANALYSIS
OCT AVE SELECTIVITY knob.
5

Selectivc Amplifier Section.
The selective amplifier section is switched in by means of the FUNCTION
SELECTOR switch, see also the block dia gra m Fig. 1.1. When the switch is in
one of the positions "Freq. Analysis" or "Auto" the instrument operates a,
a narrow band analyzer, which can be co ntinuously swept through its entin ,
frequency range 20- 20000 Hz.
The frequency characteristic of the band-pass filter can be adjusted by
the switch marked FREQUENCY ANALYSIS OCTAVE SELECTIVITY . Typ·
ical response curves are shown in Fig. 1.3 where fo is the ce nter fr equency
of the filter i.e. the frequency to which the Analyzer is tun ed .
Around the FREQUENCY ANALYSIS OCTAVE SELECTIVITY knob the at-
tenuation 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 Sclectivity in dB
20
25
30
35
40
max. approx. 45
3
dB Bandwidth in Perccnt
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
D,S
0,4
0,3
0,2
~
~
.---
0,1
~
45 40 35
("Max ." )
---
~
----
V--
30 25 20
"octave Selectivity dB"
"60''3'-
Fig. 1.4. Curve showing the correlation between the setting of the knob
OCT AVE SELECTIVITY and the filter bandwidth expressed in 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 stab ili ze the amp lifi ers a certa in amo unt of linear
negative f ee dback is also introduced . Each amp li fier cont a ins a casco de
coup l ed twin triode, a " bridge " tube and a ca th ode follower ( one half of a
tw in triod e) .
The input signa l to the first amplifi er is fed to the "u pper " half of th e
c
ascode and th e lin e ar ne g ative fe edba ck is introduced via the " br idge" tube
to th e cathode of the "l ower" part of the c ascode.
Th e sel ect ive feedb a ck circuit is shown in Fi g. 1.5. It cons ists of the " bridge"
tub e, a resi st ance-capaci tan ce ne twork of the "W ien-B rid g e" type and a
c
athode follow er. Th e . ou t put voltage from the first se l ective amp lifi er is
taken from the plate of the " bridge " tube a nd fed to th e second se l ect ive
amp li fier via the cathode follow er. To obtain the required amount of feed-
+H.T.
Vi nput
Bridge
tube
.H.T
V feedback
Cathode
follower
Voutput
't60195
Fig. 1. 5. Basic schematic di agram of the "Wien-Bridge " arrangement used in
the selective f eedback circuits of the Freque n cy Analyzer Type 2107.
back, the fee dback voltage, Vt ee dback developed in the Wi en Bridge is fed to
the grid of the " lower " par t of the cascode. The ex t ens ive use of cathode
followers in the se lective amplifiers has been nec e ssary to ensure correc t
impedance matchin g in the circuit.
7

The Wien Bridge consists of two pure resistors (H and 2R) and two arms
containing a series RC network and a parallel RC network respectively .
Although the DC supply for the "llridge" tube is inserted between the pure
resistors, the bridge acts as a closed bridge with regard to AC, because of
the 200 flF capacitor (C
e
). At a certain frequency f. = __ 1_ the feedback
2n RC
voltage, (V t.edbOOk), is zero, and consequently the gain of the selective ampli-
fier section maximum. At other frequencies the feedback voltage, (V toedb'.')'
is great. In this way the desired selective frequency characteristic of the
Analyzer is obtained.
The second selecth'e 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
OJ 0 .2
_-L.
fo
~
0 .5
/"
I
2
Fig. 1.6. Typical frequency rejection curve.
5
10
16109J
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 last 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 the "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
0.5 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 cin :uit can he brought in balance for
8

any position of the frequency scale pointer. An attenuation of 70 dB approx.
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 potentiometers
are provided. They adjust the gain of the selective amplifier section and are
placed on the back of the instrument. One of them is marked FREQ.
REJECTION - LEVEL ADJUSTMENT, and the other FREQUENCY ANA-
LYSIS - LEVEL ADJUSTMENT, see Fig. 2. 2.
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 MQ as measured on
the EXT.
FILTER OUTPUT socket. The RANGE MULTIPLIER attenuator
consists of five selected resistors with a ratio of 10 dB between two con-
secutive switch positions, and a trimmer capacitor for frequency character-
istic compensation. The output amplifier is a thre e-stage RC coupled ampli-
fier with negative feedback. The feedback, and thus the amplification, can be
adjusted by means of the two screwdriver-operated pot e ntiometers, whi ch 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
socket the output stage consists of a cathode follower . In addition capacitive
feedback is accomplished through an adjustable 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 . *)
The output cathode follower is also coupled to the meter circuit. This
circuit consists of diodes and resistors and gives the meter rec tifier a
characteristic which ensures true RMS rectification for any signal with a
crest factor of five or less.**) A switch in the rectifier 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 0.2 rnA. It satisfies th e dynamic require·
ment s for precision sound level meters as recomm e nd ed by I.E.C.
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 and
*) For more detailed inlormation see page ()'7. B & K Technical Review 1'0. 3 J~ly 1 ~5~ .
•• ) For more detailed information on this circuit see B & K Technical Review, No . ~ July
1958.
9

for the voltage supply to the condenser microphone socket, one for the
reference voltage and two for the filament voltage supply. DC heating and
special compensation arrangements have been employed on critical tube
circuits to decrease the hum level.
The polarization voltage supply for condenser microphones 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 a few volts on either side of 200.
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 switched for frequency analysis (FUNCTION SE-
LECTOR in position "Freq. Analysis" or "Auto") and turned to the fre-
quency 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
there 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 the input amplifier a visual indicator is connected in parallel
with the output of the input amplifier, as previously described. The indicator
lights up when signal peak voltages on this point exceed 4.5 volts (3.16 V
RMS sine-wave) i.e. 10 dB
higher than the 1 V RMS sine-wave, as stated
for 0.1 % nonlinear distortion. The 4.5 volts peak voltage indication limits
the measurements to signals with crest factor f. lower than 4.5. which also
is the highest crest factor allowable at full RMS drive. The higher peaks in
the signal have to contain a certain energy to be indicated. When for
example measurements are made on noise signals with Gaussian distribution
the indicator will only react for noise peaks, which are lower than approx-
imately 2.5 tim es the RMS value, i.e. f. lower than 2.5.
To be able to check on how far the input amplifier is driven in making
selective measurements, the FUNCTION SELECTOR of the Analyzer should
first be set to position "Selective Section off" and RANGE MULTIPLIER on
"0 dB, x 1". The RMS average or peak drive of the amplifier can then be
read on the indicating meter. Full deflection corresponds to 1 volt on the
10

output of the input amplifier. From the above can be seen, that in selective
measurements, when the input amplifier is driven to maximum, the sensitivity
of the Analyzer can only be increased by RANGE MULTIPLIER.
Mechanical Parts.
The continuous frequency scan of the Analyzer can be operated manually as
well as mechanically. For the latter method 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 volls. 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 Indi""t'nr --~
Polarization Voltaa,e - ~
Condenser Mic
Input Pot
Input
<;wiiloh, ---~ _
Sensitivity
Condenser Microphone
Amplifier lin out -----"
Ext Filter Inn"I .----"
We ighting N.lwn,'k ~-----'
Frequency R,,'n. ·-~
Frequency Tuning
2107
Meter
~--- -- Powor
/""--- Meter SwitCh
-
'. 7-II-- ------ "loter Range
------ Recorder
Function
Seledor
------- R'anae Multiplier
Sensitivity
Amplifier Input
Ext. Filter Output
Frequency Rejection
Balance
Frequency Analysis
Octave Sensitivity
J,.60192
Fig. 2.1. Frequency Analyzer Type 2107 with control knob identification.
Front Plate.
12
OVERLOAD
INDICATOR:
POLARIZATION
VOLTAGE:
Indicates for peak voltages higher than 4.5 V, i.e.
10 dB above 1 V RMS , on the output of th e input
amplifier.
For measuring the microphone polarization voltage.
A DC
voltmeter with an internal resistance of at
least 20000 ohm/volt should be connected between
this terminal and ground (chassis).

CONDENSER
MICROPHONE:
INPUT POTENTIO-
METER:
INPUT SWITCH:
SENSITIVITY,
CONDENSER
MICROPHONE:
Input terminal for the B & K Condenser Micro·
phones (Cathode Followers) and Preamplifiers.
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 al . tt nuator METER
RANGE.
"Condenser Microphone".
Screwdriver operated potentiometer, for adjustment
of sensitivity, when input CONDENSER MICRO·
PHONE is used.
AMPLIFIER INPUT: The signal is applied to the aUenuator METER
RANGE
either direct or via the INPUT POTENTIO·
METER, depending on position of INPUT SWITCH.
EXTERNAL FILTER
INPUT:
WEIGHTING
NETWORK:
Intended for connection of external filter input,
parallels the output of the input amplifier.
Note: A DC voltage of approximately 75 volts is
pr esent. Do not drain more than 1 rnA DC.
"Curve A", "B" or "C" is switched in.
Connected in series with the selective amplifier
section when FUNCTION SELECTOR is set to
position "Freq . Rejection", "Freq . Analysis" or
· 'Auto".
" Linear, 20-40000 ", a network is switched in
cutling off below 20 Hz with a maximum slope
of 18 dB/octave.
"
Linear, 2-40000" the Analyzer is switched as
linear amplifier, when the FUNCTION SE·
LECTOR is set to position "Selective Section
Off".
"Ext. Filter". External filter connected to EX·
TERNAL FILTER INPUT and EXTERNAL
FILTER OUTPUT is switched in.
13

14
FREQUENCY
RANGE:
FREQUENCY
TUNING:
POWER:
For selection of the six frequency ranges.
For setting of frequency within the ranges of
FREQUENCY RANGE
for analysis and rejection.
For switching off and on the power · for the
apparatus.
METER SWITCH: For selection of the three different meter indicating
METER RANGE:
RECORDER:
RANGE
MULTIPLIER:
SENSITIVITY,
properties
"Average"
"Peak" (half peak-to-peak)
"RMS"
The three positions (" Fast" ) to the le ft give 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 altenuator, 10 dB. Inserted between selective
amplifier section and output amplifier.
AMPLIFIER INPUT: Screwdriver operated potentiometer for adjustment
of sensitivity when socket AMPLIFIER INPUT is
used.
EXTERNAL
FILTER
OUTPUT: Intended for connection of the output of an exter-
nal filler. Is switched in circuit with the input of
the selective amplifier section when WEIGHTING
NETWORK is set to "Ext. Filter" position .
FREQUENCY RE-
JECTION BALANCE: To obtain maximum rejection of a signal selected
on th e Frequency Tunin g scale, with the FUNC-
TION
SELECTOR set in the "Freq . Rejection"
FREQUENCY
ANALYSIS OCTAVE
SELECTIVITY:
position.
To select six different degrees of selectivity (band-
width) 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 frequ e ncy of which is selected
on the Frequency Tuning scale. Six different
bandwidths can be chosen by the FREQUENCY
ANALYSIS, OCTAVE
SELECTIVITY switch.
"Auto". Same data as obtained in the "Frequency
Analysis" position but an electromagnetic
clutch is operated, clutching in the remotely
controlable and mechanical frequency scanning
arrangement.
Rear of Instrument. (Refer Fig. 2. 2)
MAINS VOLTAGE
SELECTOR AND
FUSE HOLDER:
The fuse should be of 1.5 amp. (medium lag).
Mains voltage selector
and fuse holder .
L- ____________ ---' 16Noo
Fig. 2.2. Rear view of Frequency Analyzer Type 2107.
15

16
, ADJUSTMENT PO-
TENTIOMETERS: 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.
FILTER REMOTE
CONTROL:
For synchronous operation of the Bandpass Filter
Set Type 1612 (2112). When the Filter Set is used
as external filter for the Frequency Analyzer, ex-
tremely high attenuation is obtained outside the
pass-band. See page 30.

Operation
Sensitivity Adjustments
1. Check that the instrument is set to the correct power voltage. Switch on
and allow a few minutes to warm-up .
2. Set the knobs listed in the following positions :-
INPUT SWITCH to " Direct"
WEIGHTING NETWORK
to "2--40000 Linear"
FREQUENCY RANGE to
"20-63"
FUNCTION SELECTOR
to "Selective Section off"
FREQUENCY ANALYSIS
OCTAVE
SELECTIVITY to "20 dB"
RANGE MULTIPLIER to "X 1 (0 dB)"
METER SWITCH to " Fast, RMS"
METER RANGE to "ReL"
3. Adjust the SENSITIVITY AMPLIFIER INPUT until a meter deflection to
the red mark on the me ter 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 ADJUST-
MENT at the rear of the instrument (Fig. 2.2) until this is achieved.
8. Set
FREQUENCY RANGE to "2 00-630 "
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 such deflection is
obtained.
Voltage Measurements.
To use the Analyzer as a normal VTVM apply the following procedure:
1. Check the sensitivity of the Analyzer . See " Sensitivity Adjustment" item)
through 3.
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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 th e AMPLIFIER INPUT
of the Analyzer. (The RANGE MULTIPLIEH switch should, when
possible, be in either of the two positions "X 1 (0 dB)" or "X 0.3 (- 10
dB)").
3. Read off the meter. Full scale sensitivity is equal to the METEH 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 Hz
to 20000 Hz. To adjust the Analyzer for measurement apply the following
procedure:
1. Check the sensitivity adjustment. See "Sensitivity Adjustment" above.
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
AMPLIFIER INPUT is used for rela tive measurem e nts.
3. Set the WEIGHTING NETWORK switch to "Linear, 20-40000" if normal
frequency analysis 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 HANGE 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, HMS".
9. Adjust the METEH 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 0.3 (-10 dB)").
10.
Switch the FUNCTION SELECTOR switch to "Frequency Analysis".
11. Turn the 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
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Analysis" above. If it is desired to directly measure the distortion factor,
app ly the following procedure:
1. Check the sensitivity adjustment. See "Sensitivity Adjustment" above.
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 Lhe WEIGHTING NETWORK switch to "20-40000".
5. Set the FREQUENCY RANGE two ranges away from the frequency
range which con t ains the fundamental frequency of the input signa\.
6. Set the FUNCTION SELECTOn to "Freq . Rejection".
7. Set the RANGE MULTIPLIER to "eX 1 (0 dB)".
8. Set the 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
sca l e) 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 0.3 (-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 th e
FREQUENCY REJECTION BALANCE, fine adjustment to minimum
meter deflection sho uld 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.
H a deflection below "3" on this volt scale is obtained, turn the RANGE
MUL TIPLIER 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
low er volt scale is obtained, turn the RANGE MULTIPLIER further
counterclockwise by one position. The upper volt scale "10" now cor·
responds 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 us ed with the Brliel & Kj:er Condenser Microphones, how·
ever, the meLer reading can be read directly in dB SL (decibe l sound level ).
To do so apply the following procedure:-
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