High pitched noise that isnt being picked up on scope?

[PRR]

Not being able to change the triggering sounds very 1950's.

"the scope is DSO188."

DSO188, mostly $35-$47.

It may just be too small to set trigger mode, with human fingers....

Trigger mode: Auto
Size: 57 x 34 x 11 mm
Weight: 40 grams

 

[MarcelvdG]

Apparently it has a suspend button: "At any time, the waveform display (pause function) is frozen". If it then only displays the last trace it has captured, you may be able to see something that's too small to trigger on.

 

[Mooly]

I don't think you stand much chance of seeing this on the scope you mention, but if it is audible then it should be pretty easy on a conventional scope of decent bandwidth if you handle the controls correctly.

 

[phofman]

I do not know in this case, but often faint signals are audible because ear is averaging the noise. There are tests with audible signals encoded in dither. I do not think such signal would be discernable on single scope trace. But any soundcard with Arta/REW/even spectrogram in audacity will identify the peak easily.

 

[Mark Tillotson]

Have you compared it with a 15kHz test tone of the same perceived volume?

Is the scope in full bandwidth mode with probe set to 10x mode?

Could this be an intermodulation product from some higher frequencies beating?

 

[MarcelvdG]

I do not know in this case, but often faint signals are audible because ear is averaging the noise. There are tests with audible signals encoded in dither. I do not think such signal would be discernable on single scope trace. But any soundcard with Arta/REW/even spectrogram in audacity will identify the peak easily.

You can definitely look deeper with a narrower noise bandwidth, so just about any kind of spectrum analyser (hardware, software or biological) will beat a scope when it comes to detecting faint tones in noise. Still, you usually need more SNR to properly trigger a scope than to see something on a single-shot trace.

 

[givemeyoursoul]

There is a high pitched ringing (~15khz) coming from my system which seems to fluctuate in volume slightly, almost like tinnitus , which I assumed it was after checking on scope and seeing absolutely nothing.

But after checking more thoroughly it is definitely the system, test tones of any frequency show up clear as day, rapidly changing waveforms like music or noise still show up clearly even if the scope cant track them.
How could it be that this noise is not being picked up at all on the scope?

Also I could still hear the noise through the headphones as the scope was attached.

"The capacitors in the 35th precinct are screaming..."