Mystery

[gar]

211225-2403 eST

ramsy:

I am seeing discrete pulses with a carrier frequency. There are long, but of variable lengths, periods of low noise level between the pulses that I see. I now have an approximately tuned resonant circuit of low Q that filters out a lot of unrelated signals.

What I am seeing are definitely man made signals, and presumably have a purpose. Without a screen room these unwanted signals are not something I can remove unless I was the source of the unwanted signals.

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[ramsy]

Underground or cave radio has a frequency range of 300–3000 Hz.

 

[synchro]

Background noise between noise pulses is around 2 millivolts. These are noise pulses to me, but are a valid signal to somebody else. These signals can not be random, there is too much structure to them. They are clearly not white Gaussian noise.

The Y axis has a BNC to binding post adapter installed. The input voltage source is a 5 ft long twisted pair shorted at the input end with about a 6" diameter 1 turn loop. Over a small range loop diameter did not much change the signal level.

Is it possible that the digital signal processing and data processing circuitry within the scope itself is the source of the observed waveforms? If you haven't already done so, you could move your loop probe near body of the scope at diferent positions and orientations to check whether it has a significant effect on the signal level.
Also, if you could insert a coax cable between the scope and your binding post adapter that might provide some additional isolation to radiated signals close to the scope, beyond what the twisted pair provides.

 

[gar]

211226-1`449 EST

synchro:

Not an easy experiment to run because shielded cable adds capacitance rapidly.

However, the nature of the observed waveforms almost certainly eliminates the possibility of the source being the scope.

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[gar]

211226-2141 EST

I am continuing my experiments. Presently looking thru the RF range of 3 to something over 20 MHz. Tremendous amount of noise. I have gone to battery power. Somewhat better. Next I need to go into the country. There are a lot of places in the spectrum with raspy noise.

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[synchro]

The about 20 MHz oscillation seems to have three discrete frequencies. The modulation shape of the oscillation changes. ...

Looking at the high frequency portion of my signal I have seen a clear modulation of the carrier frequency in a pulse. One pulse has a 200 nanoS duration of 12.5 MHz carrier or possibly 16 MHz, followed by a 180 degree phase shift of the carrier for about a comparable duration. Not all pulses have this 180 shift.

I am not seeing a relatively constant amplitude of the signal. What appears to be the sync portion of the signal is almost always the strongest part. Sync being the first part. Clearly some signals have the phase reverasal at 200 nanoS, and others do not. Clearly a man made signal with information contained in the signal.

There seems to be about a 17 microsecond spacing between what appear to be repetitive similar pulses. This is a 58.8 kHz rep rate. A pulse appears to have a carrier frequency somewhere near 15 MHz, a pulse duration of 200 nanoseconds, and sometimes followed by at least one 200 nanosecond pulse that is in phase with the first pulse carrier, or 180 degrees out of phase

Perhaps you are seeing the waveform of an HF radar that uses binary phase shift keying (BPSK) modulation to effectively achieve pulse compression. Among other things, this enhances the range resolution while transmitting a relatively long pulse of moderate power, instead of the high peak power required by a traditional short pulse radar to achieve the same range resolution.
gar, it would be interesting whether you can determine if there's any pattern in the 0°/180° binary phase modulation you've observed that corresponds to any of the "Barker Codes" shown on the following webpage:

https://www.radartutorial.eu/08.transmitters/Barker Code.en.html

There are also radars that combine frequency shift keying (FSK) and/or frequency hopping with PSK. It sounds like your waveform might have some FSK occurring in it because of the three discrete frequencies that you are seeing.

If this waveform is from a radar, then the question remains where it is coming from. HF radar is somewhat unusual, and has been used in over the horizon radars such as the "Russian Woodpecker" that was powered by the Chernobyl reactors. Also, it apparently has applications in oceanography. In your case, gar, perhaps some research might be underway at U of M that you can observe on your scope because of your proximity to it.

 

[gar]

211227-1703 EST

synchro:

The Barker code is a pseudo random signal. I am not familiar with Barker's specific work. However, I was involved in pseudo random sequences starting in 1953. This was on classified DOD contracts.

I have taken my Panasonic 0.550 to 30 MHz receiver and looked at various parts of the range for anything that might correlate. Nothing pops up. But there sure is a great amount of various kinds of noise across the spectrum. From sounds on the receiver it seems there is a lot of spread spectrum stuff out on the air waves.

I believe the specific signals I am seeing are from the power line system. There is structure to the signals, but for what purpose I have no idea.

Yes these could originate at the U of M. I have had very little contact with the U of M since 1961. All my old professors have now died, and my boarding house associates are also dead, except one roommate. My major contact with U of M is using the hospital and its associates. In the last couple years I have received a pacemaker, had my heart probed ( a totally blocked artery ), cataract surgery, and various other things. At least half of my neighbors are U of M doctors or dentists.

To go to most U of M locations is quite difficult, parking is the problem. Yet in some other aspects there are some nice road paths around town that do not exist in many college towns.

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[gar]

211229-0915 EST

synchro:

I have tried various coils and loops, and I have also tried going to battery power to the scope. From one pulse to the next there is a fair amount of variation. If I average 1024 pulses the pattern is quite consistent. The highest peak is about 40 millivolts. This is not a random uncorrelated noise level. This is clearly a man made signal.

My present input is a binding post adapter to BNC. The input loop is two 30" test leads plugged into the binding posts, and the other clip ends clipped together. It is a very imprecise coil.

Do any readers of my post see anything like this on their scopes.

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[gar]

211229-1555 EST

My latest experiments. All main panel breakers turned off. Main fuses left in place. Rigol scope on 12 V DC battery via an inverter. Input to Y axis is previous said loop of two test leads. Time base is scope internal sweep generator.

Result:

1. There is a pulse of the general nature described previously. I will call it a sync pulse, or at least a marker.
2. This pulse repeats every 1/60 second ( 16.7 millisecond period ). There is a lesser magnitude one at the 8.3 millisecond point.
3. This larger pulse has a magnitude of about 4 V.
4. There are less high pulses spaced 10 microseconds apart. With the first pulse after the high pulse starting about 7 microseconds after the big pulse.
5. The large pulse group has a carrier frequency around 18 MHz. Within a pulse the oscillation frequency seems to drift around, or is designed to do so.

Can anyone else see this kind of stuff?

Because of the high amplitude of the said sync or marker pulse I am able to sync from it.

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[gar]

211229-2020 EST

The magnitude of the pulse implies it is locally generated. Thus, could this imply something from the smart meter, or a neighbor generating something.

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[gar]

211229-2106 EST

The next bit of information is:

Scope is still on battery power, X time base is still synced off of the large high frequency pulse, and now I have connected the scope chassis via the second Y axis probe common to my AC power neutral, and the X10 probe to one of my 120 V hot lines. Doing this has made no change in the signal on the first Y channel, and sync is still retained.

The 60 Hz sine wave zero crossing, or at least very close, correlates to the large high frequency pulse. Thus, the signal I am looking at is correlated to the AC power line.

So more reason to think that some of the signals I am seeing originate from my my power meter.

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[ELA]

211229-2106 EST

The next bit of information is:

Scope is still on battery power, X time base is still synced off of the large high frequency pulse, and now I have connected the scope chassis via the second Y axis probe common to my AC power neutral, and the X10 probe to one of my 120 V hot lines. Doing this has made no change in the signal on the first Y channel, and sync is still retained.

The 60 Hz sine wave zero crossing, or at least very close, correlates to the large high frequency pulse. Thus, the signal I am looking at is correlated to the AC power line.

So more reason to think that some of the signals I am seeing originate from my my power meter.

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Build yourself a high pass filter with a 60 hz notch rejection addition. That will allow you to view the signals of interest directly, with greater resolution, if you believe they originate from the power line.

 

[gar]

211231-1651 EST

ELA:

I see no reason for a notch filter. What I am picking up is primarily capacitively coupled or RF radiation. My tuned coil is only connected to the power line via the scope grounding path.

The signal I am seeing clearly seems to be synced to my 60 Hz line for part of its modulation.

The highest frequency seems to be about 4.4 MHz as I have my coil and capacitance tuned. The capacitance is 321 pfd, and I have not measured the coil inductance yet. The 4.4 MHz is from the scope.

This carrier frequency is amplitude modulated with possibly an exponential rise of 1.5 microseconds and an exponential fall off 5.5 microseconds to where the next 1.5 rise starts.

Then there is another form of amplitude modulation, and possibly frequency, that I assume contains data of some sort.

There is apparently an approx 2 millisec period near the AC zero crossing, both plus and minus slopes, where no data is transmitted.

Signal levels of the RF are around the 10 to 20 millivolt range.

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[gar]

211231-2103 EST

On my shortwave receiver I get a strong signal at about 4.4 MHz with a very rough modulation signal. This may very well correlate with what I am seeing on my scope. Also there are number of different frequencies with very rough modulation spread thru the high frequency spectrum. May imply a lot of spread spectrum signals. Does anyone else see or hear these signals?

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[gar]

211231-2135 EST

Using a frequency calculator I get:

321 pfd and 2.6 micro henrys frequency = 5.5 MHz, at least in the ballpark.
2.6 microhenrys and 4.4 MHz = 503 pfd, and in the ball park.

Tuning closer to 4.4 MHZ might have produced a greater displayed signal. Fundamentally my tuned circuit was quite low Q.

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[Fred B]

Just a question, dont really know much about what you're experiencing my only real experience with a scope was in automotive diagnostics, but find your discussion fascinating. Is this a totally new phenomenon, or just first time seeing while "playing" with your scope? Another words have you viewed your scope within those ranges that you now see a signal, before without having a signal displayed?

 

[Fred B]

Here is a thought, don't know what this would look like on a scope, but, what about those plug in rodent and pest deterrents? I know they produce a lot of interference on my circuit tracer and fox and hound wire finders. Even when a close neighboring house has one I can pick up some of the signal.
Have you tried taking your scope and testing in a much different location? Might tell you if it is a localized phenomenon or more associated with your scope.

 

[ELA]

Is this a totally new phenomenon, or just first time seeing while "playing" with your scope? Another words have you viewed your scope within those ranges that you now see a signal, before without having a signal displayed?

Gar,
Too add to what Fred is asking
Do you understand what Aliasing on a digital Oscilloscope means? If not please goggle it.

I have to ask once again exactly what it is that you are troubleshooting? It seems as though you were initially experimenting with a coil antenna in attempts to view an intended induced signal?? Now you are interested in understanding the source of an unknown/unintended signal. An induced signal that masks your original experiment intent.
You mentioned you suspected the source as the power line. Thus the suggestion to use a filter and view the signal on the power line directly ( why a 60hz rejection notch filter was recommended). With that setup you can then attempt to measure the relative signal amplitude at various places in the house and possibly get closer to determining the source.

If you really want to view induced signal in a coil antenna the OScope maybe the incorrect tool ( 1/10 Meg input impedance). A Spectrum Analyzer ( 50 ohm input impedance) is likely a better tool depending upon the intended induced signal characteristics. Of course the learning curve for a Spectrum Analyzer is even higher than for a DSO. Also expensive for an experimenter.
I believe I read that your scope may have a 50 ohm input setting. Have you tried using that setting? If you did that will show you that you are likely using the wrong tool for monitoring unknown induced signals, without also using a filtered pre-amplifier.
Whatever your original intent was may require filtering/amplification to reduce these unintended signals masking whatever your intended signal was.

 

[gar]

220101-1057 EST

This morning's experiment clearly shows that the many signals, meaning in different frequency ranges, are from the power line.

This morning I pulled the main fuses. This creates a 6" gap between the hot power wires and the house circuit wiring. Except there is some capacitive coupling between wires because all wiring enters the top of the main panel. This greatly reduced the spread spectrum noise I was hearing thruout the low high frequency spectrum ( 3 to 20 MHz range ).

I did find a fairly large wide band noise signal around 5.5 MHz as well as the one just above 4 MHz. And there are other similar signals at other frequencies. To an extent they block out most other communication signals except for high power transmitters.

At some point I will take the short wave receive out in my car and determine what I hear.

I am still interested in whether anyone else is experiencing what I see or hear.

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[gar]

220101-1123 EST

ELA:

My problem is excessive interference with bench measurements I am making.

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