Home » Uncategorized » Device testing continues…

Device testing continues…

Follow World Hum Map and Database Project on WordPress.com
Follow World Hum Map and Database Project on WordPress.com

I am slowly learning. After hearing back from George G. regarding some initial concerns, here is a screenshot that shows me turning on the unit at t=5 seconds, then approaching an active wall outlet and rotating the device a few times. You can see the vertical axis here. This makes more sense. I’m surprised that the mains don’t dominate the spectrum, given that I am surrounded by it in this room and in this house. I’ll keep you all posted.

Screen Shot 2017-07-24 at 3.48.00 PM


7 Comments

  1. jimvandamme says:

    You’re surrounded by electronic gadgets which pull nonlinear current waveforms out of the mains and full wave rectify them into 120 Hz harmonics. Play with a light dimmer and see how it changes. I once recorded a light dimmer dozens of feet away.

    Would you send me a schematic of George’s gadget? If you’re still thinking that there’s an external stimulus, I’m interested.

    • Okay, but my question is this: why, when the device is sitting on a table, is there no spectral line at 60 Hz, but there are all those other lines up and beyond 22 kHz, yet when I approach the outlet, the 60 Hz line appears and the other lines are still there? I’m about to go outdoors and slowly turn in a circle and then check what results.

      • jimvandamme says:

        Your loads are balanced, i.e., the current in the hot wire is balanced by the current going the other way in the neutral wire. Anything that is unbalanced, like a ground fault, will radiate because it makes an antenna rather than a balanced feed line. If you’ve ever taken apart a GFCI, that’s how they work: a little toroid senses both currents and sums them together. any unbalance means a ground fault.

        When you approach the outlet, you’re a little nearer to one side of the line and it doesn’t balance as well. In the far field, the resultant is very low.

        Higher harmonics are going to couple better capacitively so I’d expect a rolloff on the low end. The ‘sharpness’ of the waveform is going to roll off the high end, says Mr. Fourier. So you hear that “ground loop sound” that plagues guitar amps with bad shielding.

  2. Glen – it is the power mains of course. You have 60 Hz and ALL its even and odd harmonics – the odd harmonics (including first) being weaker. The stronger lines are ALL (even and odd) harmonics 120 Hz, the second harmonic of 60. These harmonics of 120 (dominating) are even harmonics of 60.

    This is consistent with my acoustic findings where notching out 60 Hz accomplished little and I had to go back and also notch out 120.

    I wish I could say exactly why you are seeing mostly 120 Hz. I will look at this and hope for ideas from others who better understand modern power supplies, and the way they contaminate the mains.

    Of more interest are the blue lines that are NOT harmonics of 60 Hz. That is, mentally notch out the power lines. – Bernie

    • jimvandamme says:

      Good job for a comb filter if it really bothers you. Analog, digital, or software versions.

      • Jim – Thanks

        As to your assessment – outstanding.

        As to your suggestion of a comb filter – exactly.

        I have been dong this for years. For example:

        http://electronotes.netfirms.com/AES5.PDF

        Today, we would not use a CCD, but just a digital filter. Likely we want a design that is non-adaptive and correspondingly has just a bit of width about the nulls. Also a finite number of nulls, Easy.

        I will see if I can simplify the design to a few formulas.

        – Bernie

      • Here is the simplified digital notch filter procedure I promised.

        http://electronotes.netfirms.com/AN432.pdf

        It is longer than I would have supposed it would be – because I was going slowly. I think it reads easily enough.

        Note that in its simplest suggestion, if your audio software already has a notch function, you likely CAN just recycle the signal through for each frequency you wish to cancel. If you are not so lucky, it tells you how to proceed.

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s

%d bloggers like this: