Products > Test Equipment
Measuring Distortions with the Scope:What you see is not what you really have..
elecdonia:
--- Quote from: nctnico on January 08, 2023, 11:53:24 am ---
--- Quote from: _Wim_ on January 08, 2023, 06:47:20 am ---@nctnico, do you now of a signal that can be generated easily with an AWG where artifacts would appear within the effective dynamic range. Would be nice to do a side by side comparison, and also useful to see what to watch out for...
--- End quote ---
The two tone test mentioned earlier on is a good one (and also industry 'standard').
--- End quote ---
I recall Prof. W. Marshall Leach and others (Walt Jung?) using a two-tone test comprised of equal levels of 10kHz and 11kHz to demonstrate TIM (transient intermodulation distortion), aka “slew-rate induced distortion.” For systems with a very wide bandwidth the test tones may be increased in frequency up to 19kHz and 20kHz. The frequency difference between the two tones is kept at 1kHz. The resulting intermodulation distortion product always appears at 1kHz. Such a large frequency displacement makes this distortion product relatively easy to hear and measure.
Prior to the discovery of TIM, the two tones in the SMPTE/DIN standard IM distortion test were 60Hz along with 7kHz at a relative level of -12dB compared to the 60Hz signal. Non-linearity will generate sideband signals at 60Hz intervals immediately above and below 7kHz. Another similar IM test signal substitutes 4kHz instead of 7kHz for applications with lower bandwidth. In this case the distortion products appear in side bands near 4kHz.
EA1DDO:
If you need to measure a "Direct injection box" (aka transformer) audio characteristics, eg. attenuation, THD distorsion, etc.
What piece of equipment do you recommend?
Thanks
Martin72:
Hi...
I had made a small setup today to measure the amplifier tomorrow using bode plot.
Before that I had sent a 1khz sinus into the amplifier and plotted the FFT of it.
Following the discussion here, the result can not be trusted...or is it?
Or in other words, how could you make sure that what is displayed is coming from the amplifier and not from the scope itself...
pope:
--- Quote from: EA1DDO on March 29, 2023, 10:36:09 am ---If you need to measure a "Direct injection box" (aka transformer) audio characteristics, eg. attenuation, THD distorsion, etc.
What piece of equipment do you recommend?
Thanks
--- End quote ---
An audio interface with the appropriate software. Or an audio analyser if you can afford one.
BillyO:
--- Quote from: Martin72 on May 06, 2023, 09:44:44 pm ---Or in other words, how could you make sure that what is displayed is coming from the amplifier and not from the scope itself...
--- End quote ---
See if you can get a hold of a sine wave reference oscillator.
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