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H
52005-301D
primarily sensitive to ambient temperature and compensates for the effect of this on the first
thermistor.
Power
supply
circuit
9.
The oscillator has a mains transformer and a full-wave rectifier circuit, feeding the
instrument
through
a series regulating circuit employing p-n-p transistors
VTl
to
VT4.
10.
On the mains transformer T1 are two primary windings which can be linked in series or
parallel to permit operation from a. c. supplies giving between 190
V
and
260 V
or between
9i> V
and 130
V
respectively.
11.
Terminals and switch S2
at
the rear
allow
the input of the regulating circuit to be fed from
an external d. c.
source.
A series semiconductor diode MR1 protects the
instrument
against
the application of the wrong polarity.
MONITORED
A
TTENUA TOR
12.
The monitored
attenuator
consists
(Fig.
2)
of a
111
dB
step
attenuator,
an
input voltmeter
and an output circuit including a multi-ratio matching transformer.
Step attenuator
13.
The
step attenuator
provides
a range of
111
dB
in
three decades.
The three
controls of
these
permit adjustment in steps of
10
dB
from 0
up
to
100
dB,
in
steps of
1
dB
from
0
to 10 dB,
and
in
steps of 0.
1
dB from
0
to 1 dB.
The
last two
decades
can
also be
switched
to completely
break
the
signal
path through the instrument.
14.
Each decac
~uses
four symmetrical T
networks,
which
are
switched
into use
alone or
in
different series combinations to
provide
ten steps of attenuation.
Each network
has a charac-
teristic
impedance
of 600
n.
High-stability resistors are
used
throughout.
The complete step
attenuator assembly is in a separate box.
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of
monitored
attenuata
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