To measure difference frequency distortion, press . The LA102 will
quickly measure the rms level of the double tone and assume that each component is 3dB
below this level. The 70Hz bandpass filter is then used to measure the level of the
difference frequency distortion product. This absolute level (in dBu or dBV) is shown on
the bar graph, while the normalised result (relative to the reference level, as explained
above) is shown numerically (see fig. 2.18). Note that the
key must be pressed in
28
2. Manual Operation
0 500 1000 1500 2000
-80
-70
-60
-50
-40
-30
-20
-10
0
Frequency/Hz
Level/dB
Test Signal (f1 and f2)
f2-f1 2nd
order product
f1+f2 product2f1-f2 product 2f2-f1 product
Fig. 2.15 Typical Intermodulation Products from a Double Tone with
1kHz Centre Frequency, and 70Hz Separation (Nominally)
0 2 4 6 8 10 12 14
-1
0
1
Double Tone Waveform Compared with 70Hz Sine Wave
Time/ms
Output V
Fig. 2.16 LA101 Double tone Waveform compared with 70Hz Sine Wave
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