Golden Valley Electric association up here has always been very competent and eager to solve noise problems. Probably because the head of engineering for many decades was a ham. I believe he also trained his underlings well...the systems seems to be incredibly clean. This may not be the case elsewhere, but I'm very grateful for our power folks up here.
73!
Eric
On 12/5/23 06:45, Dana Whitlow wrote:
David,
As I've tried to emphasize above, all i've looked at so far is the "raspy buzz"impulsive form of noise, which I've normally tended to regard as the mostobjectionable. However, I do recognize that the "fuzzy hum" form wouldlikely turn out to be more of a problem for very narrowband analyses, whichis my usual case, if a harmonic should land too close to the signal band ofinterest.
Many of my experiments have involved a final measurement bandwidth ofless than 1 Hz, so I should be alert to this possibility.
Dana
On Tue, Dec 5, 2023 at 9:38 AM David G. McGaw <david....@dartmouth.edu> wrote:
Generally, transformers do not make noise. All the electronic loads in the neighborhood on the line will create a certain amount of harmonics, though the larger loads are required to include power factor control to minimize this. Defective insulators or branches and such across the wires do create pulse noise.
You are correct, if you can localize the source of the interference, the power company will fix it. They do not have the capability of finding it themselves so rely on us to find and report it. In New England, we have created a task force under ARRL to help, see <https://nediv.arrl.org/spectrum-protection-utilization/>, "Noise Identification".
73,
David N1HAC
On 12/5/23 10:34 AM, Dana Whitlow wrote:
Michael,
Since there is no electrical connection to the top end of the pipe,basic EM theory says that the pipe is actually irrelevant to common-mode current flows. Whether or not the pipe provides any shieldingfor E-fields is another matter, of course. I have not looked at theE-field issue, because even if the pipe is not grounded, the 40 ft ofunshielded wiring from the pole to the top of the pipe would by farbe the dominant radiator, and there is nothing I could do about it.
Your mention of the transformer itself being noisy is scary, becausethe ultrasonic test would almost certainly fail to detect such aproblem, probably making it rather difficult to persuade the powercompany to change out the transformer "on speculation".
As far as power outages are concerned, I'd love to see a county-wideoutage at night in clear WX, just so I could enjoy a dark sky for achange. But preferably in the summer, you understand.
Dana
On Tue, Dec 5, 2023 at 9:01 AM 'Black Michael' via HamSCI <ham...@googlegroups.com> wrote:
Make sure your metal pipe is grounded to the ground rod at your breaker panel.
You should see almost 0 Ohms between the pipe and ground connection.
It may be more likely coming in the wiring. Do you have an oscope you can use to see what's on the wires/pipes?
The power outage is a good clue and you may be able to get the power company to come out based on that observation.
Noisy transformers are common and they are required to replace them.
Mike W9MDB
On Tuesday, December 5, 2023 at 08:55:58 AM CST, Dana Whitlow <k8yum...@gmail.com> wrote:
Michael,
I've only tried that once, during an episode of the raspy buzz form
of the problem. I used a battery-powered AM radio in the AM BC
band so that I could use the ferrite bar antenna.
The breaker panel is located on the outside of the house, and the
incoming power comes down through a metal pipe which extends
up through the eave, with the wiring from the pole entering said
pipe through the usual arrangement used to keep rain out.
Anyway, before I turned off any breakers I moved the radio around
and concluded that the noise was manifested (at least primarily) as
a common-mode current through the metal pipe.
Next I began turning off individual breakers to see if the problem
was confined to a single circuit, but apparently it was not.
Then, with all the individual breakers back on, I opened the master
breaker, with the same result. The noise remained in all its glory.
I suspect a problem with the pole about 40 ft from the house, but
did not have an ultrasonic snooper at the time. I acquired one of
those only very recently, but have not yet put it to the acid test.
I have not yet found anybody selling giant clamp-on ferrite chokes
for "cables" about 4 inches in diameter :-)
Also, I have not yet investigated the fuzzy hum form of interference.
Dana
On Tue, Dec 5, 2023 at 8:25 AM 'Black Michael' via HamSCI <ham...@googlegroups.com> wrote:
> Can we assume you've tested cutting power to your house so you can determine if it's YOUR house causing any of the hum?
>
> Mike W9MDB
>
>
>
>
>
>
>
>
> On Tuesday, December 5, 2023 at 05:34:33 AM CST, Jonathan <emum...@gmail.com> wrote:
>
>
>
>
>
> A benefit to powerline hum (radio emissions of 60Hz and harmonics radiated by power lines) being omnipresent even in the most RF quiet locations is that you can monitor local and regional power outages very closely with a VLF receiver. A local power outage occurred around the vicinity of the VLF receiver at Spring Brook Township, PA. Here is a plot of the amplitude level of 180 Hz, a harmonic of 60 Hz, showing some power loss at ~2030UT and completely at ~2100UT:
>
>
> Here you can see the hum level in greater temporal detail. What is so impressive about this power outage is how low the hum levels got. I will be pulling the audio file and listening to this period. Unfortunately, there were no whistlers or dawn chorus, but hum levels this low are quite a treat:
>
>
> After the power outage ended, there were some interesting spikes, possibly due to inductive inrush, then hum levels returned to normal:
>
> The VLF system was on a UPS during the power outage, so there definitely is benefit to keep the system up and running during local power outages, especially if the magnetosphere decides to be generous. Power grid studies are often done using VLF receivers and the benefit is that no attachment to the power lines are required.
>
> Jonathan
> KC3EEY
>
>
>
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Remember you aren't just measuring 180Hz -- you're also seeing the noise level in your amplitudes. One of the weaknesses of an FFT.
If you want the 180HZ level you have to subtract the noise level.
Mike W9MDB
On Tuesday, December 12, 2023 at 05:50:45 AM CST, Jonathan <emum...@gmail.com> wrote:
One of the benefits of vlfrx-tools is how powerful its signal processing tools are. I wanted to investigate the power line frequency over time to understand how it varies throughout the day. With GPS timestamped and sampled aligned data, I can see how the 180 Hz harmonic varies over time. To do so, I feed the stream into a brick wall filter centered at 180 Hz that is 2 Hz wide. Then, after downsampling, I feed it into an FM demodulator, which gives me a frequency deviation output. This frequency deviation output gives me the frequency variation that I'm looking for. I downsample some more to a rate of 1 Hz/sec to decimate and plot the data.
Here is a plot of the 180 Hz harmonic over a span of 4 hours showing the deviations in hundreds of mHz:
The vertical scale is in mHz and the horizontal scale is in seconds, spanning 4 hours. You can see the deviation spanning ±200mHz which is really interesting! This might represent the variations in load on the local and regional grid.
Jonathan
KC3EEY
On Sun, Dec 10, 2023 at 9:59 PM Jonathan <emum...@gmail.com> wrote:
> Here on the day of the annular eclipse, powerline hum levels were low enough that the 180 Hz harmonic seemed to have exhibited ionospheric propagation. Notice the drop in amplitude at dawn. To me, this shows daytime D layer absorption as seen in other signals:
>
> You'll also notice a slight decrease in absorption during eclipse time which is expected.
>
> As time went on, background hum levels increased, so this ionospheric propagation can't be seen on those days. Here is a plot of the last 60 days since the eclipse showing an increase in power levels of the 180 Hz harmonic:
>
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