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Chapter
4
TECHNICAL DESCRIPTION
CONTENTS
Para.
1
Oscillator
2
Amplifier and output control
7
Feedback
9
Power supply circuit
12
Monitored attenuator
13
Step attenuator
15
Input voltmeter
19
Output matching
Block diagram of oscillator •..
Fig.
1
2
3
Block diagram of
monitored
attenuator
Output matching stage - (less
switched
internal
load)
OSCILLATOR
H 52005-301D
Page
2
3
4
1.
Basically,
the oscillator consists (Fig.
1)
of a multistage transistor amplifier, two
overall feedback loops creating and stabilizing oscillation, and an attenuator controlling
the output.
The instrument
also contains a
power
supply circuit.
Amplifier and output control
2.
The first stage of
the
amplifier
is
transistor VT5
in
a common-collector or emitter
follower
circuit.
The
input is
the net signal derived from the two feedback paths. The tran-
sistor
used is
a silicon
n-p-n
type, as are all the others
in
the amplifier.
3.
The
voltage gain
in the
system
is
provided by the second stage VT6 in a common-emitter
circuit which produces
high
gain as a
result
of a
high effective
a. c. collector load
impedance
obtained by a bootstrap arrangement;
the
collector
load resistor is not
fed
directly
from
the
d. c. supply but
from
the emitter of an auxiliary transistor
VT7
dri~en
from a further point
in the
amplifier
chain.
4.
The
two following
stages are emitter followers
vrs
and
VT9.
At
the
output of
the
first,
the auxiliary transistor
VT7
receives
it
s
drive; and
als
o
at this point diode limiter MR6 is
connected,
to
control the amplitude of
initial oscillations
at switch
-on.
The second
emitter
follower
VT9 d
r
ives
the
output stage
.
Nov
.
79
Chap
.
4
Page
1
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