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and
31 6Hz
bandwidths
are
ob-
tained
.
Further the signal is fed either to
the
selector_
circuit or
,
if narrower
bandwidths are desired, to the third
mixer
.
The frequency of the signal
is
transformed
in
this
mixer to
750Hz by mixing with a 30,75 kHz
signal.
The 750Hz signal is fed to the
750Hz band-pass filter where the
bandwidths in the range 100Hz to
3
,
1 6Hz
are
obtained.
From
the
750Hz filter the signal is fed to the
output section via a selector circuit
for the A,
B,
C and D weighting and
bandwidth compensation networks
.
From the output amplifier the signal
is fed to the RMS rectifier, where
different averaging times and a lin-
ear or logarithmic response can be
selected and further to the meter
where the level of the input signal
is indicated
.
The signal is also available at the
recorder output. A selector offers
the choice of an AC, linear DC or lo-
garithmic DC signal.
The ana lyzer is connected to the
BFO via the Voltage Controlled Os-
cillator. The signal from the VCO
which is fed to the f irst mixer is
also fed to the BFO where it is
mixed w ith a
1,
2 MHz signal to give
a sinusoidal output signal with a fre-
quency corresponding exactly to the
tuning frequency of the analyzer
.
The level of this signal can be con-
trolled automatically by means of
the compressor circuit with variable
compression speeds
.
Input Section
The input section has a direct in
-
put (standard B
&
K input socket)
and a B & K seven pin standard mi-
crophone input socket containing the
necessary
power
connections
for
B & K microphone preamplifiers and
condenser microphones
.
V ia the in
-
put attenuator having a range of up
to 90 dB attenuation the signal is
fed to the low noise and low distor-
tion input amplifier where it is am-
plified 40 dB
.
For calibration pur-
poses the amplifier has a continu-
ously var iable gain control setting
with a range of 1 0 dB
.
From the in-
put amplifier the signal is fed to the
output for external filter
,
the selec-
tor circuit and the first mixer
.
An
overload indicator is connected to
the amplifier
.
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40
50
£?0
70
80
- 7
-6 -5 - 4 - 3 -2
-1
to
2
3
4
5
6
7
Bandwidths from ce ntre frequency
17 1104
Fig. 2. Typical filter characteristics of the filter section
,._
_ _ _
3 dB
Bandwidth -----i~
2
4
6
8
3
dB
3.5
dB
10
30 40
5o
60 70 80 90 100 110120130140150160170
Hz
I . - -Effective no ise
bandwidth
------.1
17
11
05
·
Fig .3
.
Top of the filter characteristic showing the effective noise bandwidth (3,5 dB) and the
3 dB bandwidth. The relation between the two is the following
:
3 dB bandwidth
=
effec-
tive noise bandwidth
x
0,96
Filter Section
The filter section of the 2010 con
-
sists of three mixers with corres-
ponding band-pass filters providing
three
intermediate frequencies of
1,2 MHz, 30kHz and 750Hz. The
six
constant
bandwidths
in
the
range 3
,
1 6Hz to 1000Hz are ob
-
tained in the band-pass filter sec-
tions which are double 2 pole but-
terworth networks
.
The filters fea
-
ture
low distortion and high dy-
namic range
.
Fig .2 shows the filter
characteristics of the networks.
3
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