Operating Instructions-AA
501
with the 400 Hz HI PASS filter. This filter should not be
employed at frequencies below 1 kHz as erroneous
readings will result. For more information see text under
Filters in this section of this manual.
A distortion analyzer must tune out the fundamental
frequency. In the AA 501 all tuning of frequency is done
automatically. For input signals with greater than about
20% noise and distortion, care must be taken to ensure
proper locking of thiscircuitry. Inmost applications which
require higher distortion measurements (for example,
SINAD' testing) the circuitry remains locked after it is
initially given a clean signal. To perform a
SlNAD test, the
receiver under test is first given a high level input. The
AA 501 will lock onto the audio signal at theoutput. Therf
level feeding the receiver is then reduced until a 712 dB
distortion reading is obtained on the AA 501.
'
Defined in Electronic Industries Association Standard No.
RS
204A, July 1972, Electronic Industries Association,
Engineering Department, 2001 Eye St. N.W., Washington, D.C.
20006.
IM Distortion Measurements (Option
01)
Another measurement of distortion is the interaction of
two or more signals. Many tests have been devised to
measure this interaction. Three standards are
SMPTE~,
DIN4, and CCIF'. The Option 01 AA 501 is capable of
automatically selecting and performing all three tests.
To measure intermodulation distortion (IM), according
to SMPTE and DIN standards, the device under test is
excited with a low frequency and high frequency signal
simultaneously (Fig. 2-7). The output signal is high-pass
filtered to remove the low frequency component. The high
frequency tone is then demodulated, as an AM radio
signal. The demodulator output is low-pass filtered to
Society of Motion Picture and Television Engineers, Standard
No. TH 22.51, 862 Scarsdale Avenue, Scarsdale, N.Y. 10583.
Deutsches lnstitut fur Normung e V, No. 45403 Blatt 3 and 4,
January 1975, Beuth Verlag GmbH, Berlin 30 and Koln 1.
'
International Telephone Consultative Committee.
Meter
High Frequency
-
Oscillator
2958-06
Fig. 2-7. Block diagram of basic IM analyzer.
ENGLISH
2-9
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