Just yesterday my 4 year old grandson and I were playing with my scope. He put his finger on the probe end and I adjusted the sweep and amplitude to get a presentable display. The 60 Hz pickup was horrible. Since I changed my shop lights to LED's, I would have thought the Mains would have been clean. I am not going to investigate the source of the noise but it is interesting that the radiated signal is so bad.
Dan Kahn
On Friday, December 13, 2024 at 12:46:41 AM EST, Andy via groups.io <ai.egrps@...> wrote:
On Thu, Dec 12, 2024 at 06:32 PM, wn4isx wrote:
I repeat, if all you want to do is look at the 50/60Hz Mains waveform, why? There is nothing interesting about a 50/60Hz 'sinewave.'
I agree, a sinewave is not interesting - but sometimes the mains waveform is not a sinewave, and then you really really need a 'scope to see it..
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Back in college, I remember that the lab's AC mains was a very distorted wave.? We had rumors about why, but I do not recall being told the truth from a reliable source.? It was understood that there was some sort of device in the building's basement (transformer? motor-generator?) that was responsible for the lousy waveform.
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Around the same time, give or take a few years, I became somewhat interested in the AC mains waveforms mostly because of power transformers that would go up in smoke - and a few other reasons.
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It was said that anyone could tell whenever the local synchrotron was online because there would be a significant glitch at a certain point in the 60 Hz mains waveform.? I don't know if it was true but it was one of the things we had to consider.
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Also there was the time the local power company changed some HV power wiring which resulted in extremely noisy signal monitoring over rented telephone company wires (this was decades ago).? Talks with the utility company's engineers suggested that their changes resulted in a significantly bigger common-mode current through earth, of the harmonics of 60 Hz - suggesting that the 60 Hz waveform was not very clean to begin with in that section of the mains distribution network.
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These days, there are those ugly "modified" or "pseudo" sine waves that are digitally generated.
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I'd argue that using an isolation transformer could significantly change the waveform's shape and can mask the problem you are looking for.
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A 9K:1K attenuator is great - IF you can be certain which lead is always the neutral.? I hear many stories about building wiring that is not right, so I think I would not want to use that arrangement which can make the scope's chassis 'hot'.
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Use a 'scope when it's needed, and if you do, use it wisely!
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Just my opinion.
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Andy
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