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Distortion M e a s u r e m e n t :
A n amplifier stage, or an entire amplifier unit, may
be tested for distortion with this oscilloscope. This
measurement is especially variable when the slope
of a waveform must be faithfully reproduced by an
amplifier. F i g . 1 0 shows the testing of such a cir-
cuit using a triangular wave, such as is typically en-
countered in the recovered audio output of a
limiting circuit which precedes the modulator of a
transmitter. The measurement may be made using
any type of signal; merely use the type of signal for
testing that is normally applied to the amplifier dur-
ing normal operation. The procedure for distortion
testing is as follows:
A D J U S T P O S I T I O N C O N T R O L S T O
S U P E R I M P O S E W A V E F O R M S D I R E C T L Y
O V E R E A C H O T H E R
A D J U S T T O B O T H
W A V E F O R M S A R E
S A M E
A M P L I T U D E
A M P
N o . 1
Fig. 1 0 Distortion m e a s u r e m e n t
1. Apply the type of signal normally encountered
in the amplifier under test.
2. Connect Channel 1 probe to the input of the
amplifier and Channel 2 probe to the output of
the amplifier. It is preferable if the two signals
are not inverted in relationship to each other
but inverted signals can be used.
3. Set Channel 1 and Channel 2 D C - G N D - A C
switches to A C .
4. Set the M O D E switch to D U A L .
5. Set S Y N C S L O P E switch to INT and adjust
controls a s described in waveform veiwing
procedure for synchronizing waveforms.
6. Adjust C H 1 and C H 2 POSITION controls to
superimpose the waveforms directly over each
other.
S U B = D I S T O R T I O N
A M P
No. 2
7. Adjust C H 1 and C H 2 vertical sensitivity con-
trols ( V O L T S / D I V and V A R I A B L E ) so that the
waveforms are as large as possible without ex-
ceeding the limits of the scale, and so that
both waveforms are exactly the same hight.
8. Now, set the Mode switch to A D D and C H 2
Polarity of INV (if one waveform is inverted in
relationship
to
the
position).
Adjust the fine vertical sensitivity control (CH2
V A R I A B L E ) slightly for the minimum remain-
ing waveform.
Any waveform that remains
equals distortion; if the two waveforms are ex-
actly the same amplitude and same waveform
and there is no distortion, the waveforms will
cancel and there will
horizontal line remain on the screen.
Gated Rising Circuit (burst circuit)
Fig. 11 shows a burst circuit. The basic settings of
Fig. 11 G a t e d ringing circuit and w a v e f o r m s
control knobs are the same as those in Fig. 5. The
waveform A is the reference waveform and is
applied to C H 1 input.
sampled at C H 2 and compared to the reference
waveforms are sampled at C H 2 and compared to
the reference waveform of C H 1 . The burst signal
other,
use the
NOR
be only a straight
All other waveforms are
13
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