A very impractical noise-reduction method that likely you cannot use.

[Rick Law]

This was interesting.  Too bad it didn’t last:

Two nights ago, I was working with a low voltage circuit that at times goes into oscillation (about 50kHz stars at mV but saturates at 2-5V+ peak to peak).  My DMM isn’t going show the oscillation with a mere two-per-second sampling rate.  So, I had my noisy Hantek USB scope hooked up to catch the oscillation which I was try to stop.  The 6022BE at 20mV/division always shows a 5-10mV noise.  The trace is normally a thick 5-8 or even 15mV line thick line instead of a thin line, but good enough for me to catch a 50mV plus oscillation.

Low rumbles started as a storm near.  I started wrapping things up expecting a storm (like shutting down my server, my air conditioning… so on).

All a sudden, I saw the noise the USB scope normally shows was gone.  The display was a clean thin line.  I was startled for a bit, and start checking if anything came loose, is it on the right scale, checked if I grounded the probe by mistake, so forth.  I moved the mouse and a few spikes appear (triggering the scope) and some below-10mV spikes were shown on the scope’s display.  So I know the scope was working.  I moved the probe to other parts of the circuit and saw what I expect, including a part where I know other noises are present and saw those expected noise.  Everything else seem normal except the absent the normal background noise.  The trace was not a thick line but a clean thin line at 20mV/division with an occasional spike or two within the entire displayed trace.

It lasted for at most 5 minutes before the storm took the power out.  We had no power for a few hours.  When power returned, everything (including the noise) came back as expected.

It was kind of interesting.  Thunders are charged clouds meeting, dating, and arguing.  Interesting how it affected even indoor.  I can see how charged air may affect electrical noise, but I did not expect to see it affecting my measurements as it did.

It lasted long enough for me to see and confirmed that it was real.  It however did not last long enough for me to explore more.  That was very interesting.

Here is my plan to get my 6022BE to work better: get my wife may agree to move our bedroom to the basement.  Remodel 2nd floor, convert our then-former bedroom for a large Van De Graff generator.  My daughter needs to sleep in the basement too - convert her bedroom into a diesel engine room to drive the Van De Graff...  Once completed, I will have an almost noise-free cheap scope!

Now that I have a good plan.  I need to plan the work and then work the plan.

[Rufus]

Low rumbles started as a storm near.  I started wrapping things up expecting a storm (like shutting down my server, my air conditioning… so on).

All a sudden, I saw the noise the USB scope normally shows was gone.

You don't think that something you turned off was more likely to be responsible for the noise rather than an approaching thunder storm?

[Rick Law]

Low rumbles started as a storm near.  I started wrapping things up expecting a storm (like shutting down my server, my air conditioning… so on).

All a sudden, I saw the noise the USB scope normally shows was gone.

You don't think that something you turned off was more likely to be responsible for the noise rather than an approaching thunder storm?

It certainly could be something turning off elsewhere.  I did not turned anything off yet, but neighbors could turned her stuff off.

After I complete that note, I went out to smoke as I have a no-smoking house.  I also heard the familiar humming - somewhere nearby, there is some big machine of some sort.  If it is close enough to hear, EM wave (if it creates any) could travel that far. Also...the cell/microwave tower near by...

You are right.  I should hold off my order for the Van De Graaff.... 

[MacAttak]

Rufus' theory seems unlikely. I would move forward with the generator and engine room plan 

[robrenz]

My wife prefers the look of our highly polished ferrite wall, floor and ceiling tiles with the Mu metal underlayment

[Rick Law]

Rufus' theory seems unlikely. I would move forward with the generator and engine room plan 

Joking aside, not that the noise is important as long ago I accept that noise is part of the living world and I just have to live with it one way or the other --- but I like to figure things out and this one puzzled me.

Rufus' theory was my first thought, but back when I first got the scope, I actually did investigated internal (in my house) noise to the extend I actually did turned off everything in my house - even the refrigerator - and then ran the USB scope from the laptop's battery.  So I am sure the noise is within the USB Scope itself or from outside my house.

The noise stopped before I turned anything off, and since it was a few minutes before power out, it is unlikely all my neighbors turned off all their stuff at the same time just as I was deciding to do so.

That leaves a single "something big" (ie, big EM generating equipment and not small household stuff ran by neighbors), or atmospheric.  Single before it was prior to power out.  It is unlikely multiple separate pieces of equipment got turned off at the same x minutes before power outage.  (Unless a few phases went down as few minutes before household power did).  My near by cell tower within sight (< 1 mile) was still operating after the power was out, so they never did stop and so it could not be them.

Part of the reason I wrote the original post is to see if anyone else experienced atmospheric effect on their equipment(s), and see some of your reactions.  May be it was something I had not yet thought of and I can learn something new.  It would surprise me if one can actually measure the effect of a large charged cloud near by; but then again, why not?  Lightnings do release a huge amount of energy so the energy stored in cloud must be huge.

I love puzzles.  Now I am looking forward to another power outage.  I am curious what kind of noise I would pick up when no one near by has power.

[robrenz]

Might be interesting to store a couple FFT's of the the typical noise spectrum under normal circumstances. Then capture a few when this mysterious quiet zone occurs again and then compare them.

[Mechatrommer]

the pc and ups next to me if turned on, will emit a good noise, my body will become antenna of a circuit under test, feed the good noise into the circuit and having fun translating signals on the dso. now i know why people dont like to operate pc based equipments on their bench, they never told me, but now i know.

Now that I have a good plan

good plan for you and your cheapy dso, at the expense of your wife's and daughter's comfort. apart from that i believe setting up a sound and vibration proof room for an diesel engine is not cheap, so do the maintenance work and health issue thereabout.