Mystery

[gar]

220102-1319 EST

An update.

When I previously said that I did not see a reduction in the unwanted signal until I pulled the main fuses was accurate. Except that when I just turned breakers off I did not turn off one breaker. So the statement was actually incorrect. Turning off all breakers does greatly reduce the noise level. So it isn't necessary to pull the main fuses to do my search for the noise sources, and the major source of unwanted signals is within my home.

I have now placed an RFI filter in the supply to some of the noise sources.

Looking directly at my 60 Hz supply with a 10X probe I have a very clean and nearly perfect sine wave. The deviation from a sine wave is near the peak and is distortion from all of the 10,000s of computer capacitor input power supplies that load the power system. You see this in the distortion of the sine wave peak. Back in the early 1960s when I made photos of the power system waveform I did not see that distortion.

To look at my present sine wave directly it looks extremely clean.

When I look at this same power line signal with the low frequencies greatly attenuated is when I see these unwanted millivolt signals on the power line. These are seen via capacitive or inductive coupling. There are many different sources that cause these unwanted signals.

I will discuss this further later.

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[ELA]

Gar,
Welcome to the 21st Century and to common household devices with electronic circuitry and emissions.
I have identified/filtered or removed several from my home.
Here are a couple of examples: ( note the 60hz waveform is only as a reference pt for zero cross
amplitude is much attenuated)

 

[tom baker]

Can you operate your scope on battery? Eliminate any issue with ac mains

 

[gar]

220102-2013 EST

tom:

My scope I can operate off an inverter and battery, but the inverter adds lots of noise.

My 3 to 30 MHz receiver can operate directly from a 12 V battery and is thus useful.


ELA:

Your waveforms are interesting. And there is a lot of electronic stuff creating noise problems. I have apparently been able to lower some of the resonant looking signals to point where the noise may look more random. But that means turning virtually everything off in my home except for the scope.

When I get down to this low level then the shortwave radio has less problems. However, there are certain frequencies where it appears there are some spread spectrum signals.

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[gar]

220103-1141 EST

When I shut down my entire main panel, and run the 3 - 30 MHz receiver on battery power, then spectrum is greatly cleaned up. Unwanted signals from my home are now gone.

One of my local noise sources was the TV antenna amplifier. It was the source of the 4.4 MHz signal, so another switching power supply problem. Every switching supply should be required to meet FCC RFI emission requirements. For residential applications virtually everything is required to meet the FCC RFI limits.

Back in 1960 I started putting Corcom 5R3 or 5VR1 filters in all my 8 ft Slimline fluorescent lights fixtures to reduce RFI output. I still have those same fixtures, but now most have direct drive 120 V LED tubes ( the ballasts are removed, but not the 5R3s ). These seem to have more noise than with the fluorescent bulbs. I have not made any comparative tests.

So my task now is to try to filter any of these noise sources.

Presently with my scope in single cycle trigger mode I see a 3.3 microsecond period signal pop up every so often ( probably many minutes ). This is a typical damped oscillation that I observe, several cycles to rise to a peak and a longer time to decay. Still with my tuned circuit at about 4 MHz. This an approximate frequency of 300 kHz.

I have a lot of work to do to clean up my AC power.

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[gar]

220109 EST

A waveform I created a long time ago for my website, Photo P1 of https://beta-a2.com/cat-5e_photo.html , shows a propagation velocity of about 750 ft / microsecond for CAT 5 cable. The velocity of light in free space ( a vacuum ) is about 983 ft / microsecond. The velocity of light in free space is 300 meters / microsecond. Propagation along an insulated wire is generally in the range of 70 to 75 % of velocity in free space. If you check different manufactures of CAT 5 cable you will see these kinds of differences.

Note: that 1 meter = 39.34 " and 12 " = 1 foot, so the ratio is 39.34 / 12 = 3.2783 . So velocity of light in free space is 300 * 3.2783 = 983 ft /microsec.

The waveforms I see around my home have a longer decay time than just that from power cables.
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