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Author Topic: Solar panels causing RFI from afar?  (Read 3853 times)
KE2KB
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« on: October 14, 2017, 06:59:00 AM »

Hi;
I have concluded by experimentation that the spikes every 40khz during daylight hours are originating from solar panels. So it makes sense that the spikes would disappear when the sun goes down... but that is not exactly the case.
After darkness has fallen here on the east coast (NJ), I am still seeing/hearing the spikes on my SDRPlay. The difference is that the spikes are not as steady in amplitude as they are during local daylight hours. So it appears to me that the solar panels in other parts of the country are radiating and propagating. Once night has fallen in the central US, the spikes have completely disappeared, so it appears that it the farthest they are propagating.

Has anyone else made this observation?

Frank KE2KB
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N3QE
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Posts: 4944




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« Reply #1 on: October 14, 2017, 07:35:20 AM »

Noise environment does indeed change a lot night vs day on the bands. Lots of time at night the atmospheric noise on low bands is enough to mask some local RFI that is actually present 24x7. As winter comes and low band atmospheric noise drops, you may be hearing RFI that was there in the sumemr but was always covered up by nighttime atmospheric noise.

What bands are you hearing the 40kHz harmonics on at night? 40M, 30M? Usually the house panel wiring is not long enough to work as an effective long-distance radiator on 80M.

At night, solar battery installations run in a different mode when the batteries are discharged and they convert DC to AC and these inverters likely sound different/different RFI.

I'm not sure we need to blame solar installations until we've eliminated all the many crappy switching power supplies and grow-lights that make nasty RFI.
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AA4PB
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« Reply #2 on: October 14, 2017, 07:48:35 AM »

Solar panels themselves are linear devices and don't emit any RFI. The charge controllers that limit charge to the batteries are often switching devices that can create varying amounts of RFI depending on the state of the batteries and the output of the panels. The inverter that converts the DC battery voltage to 120C AC are switching devices that can create RFI. I'd be surprised though if any part of a residential solar system would radiate RFI half way across the country. It's more likely to be some one in the neighborhood.

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Bob  AA4PB
Garrisonville, VA
K0UA
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Posts: 1468




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« Reply #3 on: October 14, 2017, 10:19:38 AM »

I don't know what it is but I have the same thing he is describing here.  Unstable 40khz signals that drift up and down.  It isn't in my house and the nearest neighbor is about 250 feet.  I am not sure what it is, but it arrived about a year ago. Most noticeable 160 thru 40 meters, and getting considerably  weaker as you go up in frequency.
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KE2KB
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« Reply #4 on: October 14, 2017, 11:16:55 AM »

The RFI I have been experiencing is mainly on 40m, but I have also heard it on 80. Starting with 7001Khz and every 40Khz through 40m, and I think it's on 30m as well, but since my antenna is not going to receive as well at non-resonant frequencies, I may just not hear it on other bands.

I was thinking more along the lines of solar panel arrays than residential installations. Couldn't there be enough wiring in those systems to radiate on 40m?

I really wish I had a 40m loop and a portable radio that could receive this RFI, so I could walk around my neighborhood with it.
If I could locate a harmonic on 2m or 70cm, I could use my HT. I could even build a small Yagi for those bands.

I'll hook up my SDRPlay to my 2m antenna and see if I can find any harmonics up there.

In the mean time, I wait for a power outage. I have a good UPS on my computer that will keep my SDR running for at least 30 minutes.
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K0UA
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« Reply #5 on: October 14, 2017, 11:50:48 AM »

This is where an FT817 and a small loop sniffer antenna would really come in handy.
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K0UA
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« Reply #6 on: October 14, 2017, 12:04:34 PM »

Here is a look on 80 meters with as you can see a bandwidth of the spectrum scope set to 500Khz each way, so a 1 meg look.  You can see the vertical lines on the waterfall.  I have the RF gain back a little to add some contrast to keep from washing out the scope.  You can also see how my antenna falls off on the edges in its response.  Click on each thumbnail to see a larger photo on the post image site


« Last Edit: October 14, 2017, 12:13:35 PM by K0UA » Logged
K0UA
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« Reply #7 on: October 14, 2017, 12:05:40 PM »

Here is another now looking 100K each way

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K0UA
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« Reply #8 on: October 14, 2017, 12:06:57 PM »

Now this one at 25khz each way clearly shows two of them.

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K0UA
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« Reply #9 on: October 14, 2017, 12:08:45 PM »

And the final one where I have one tuned in to the center frequency shown, and the audio bandwidth set to 3.1Khz showing the spur in the audio scope waterfall as well as the audio oscilloscope display





Looking at this last photo, the spur has moved over 1khz in the time it has taken me to post these.
« Last Edit: October 14, 2017, 12:12:07 PM by K0UA » Logged
KE2KB
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Posts: 653




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« Reply #10 on: October 14, 2017, 03:14:17 PM »

I guess it could be that all the RFI I have been hearing/seeing is local after all. Today it is overcast, and the signals are weaker. I wish I could have an FT817, but the lowest price I can find is for a used one on Ebay for $480 - and that's only the current bid.
Perhaps I could rig up my SDRPlay to my Android phone. I read somewhere about a way to do it. There is apparently an app, and then I would just need the proper cable. I would need an external battery source, but that wouldn't be a problem. I have a backpack that could carry all of that.

Might be worth looking into, although I doubt there is anything I could so about the RFI once i found its source.

What happened to part 15? I thought that any device that has the potential to radiate energy needed to be tested and accepted so as not to cause interference to other devices or radio services.
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AE5GT
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« Reply #11 on: November 20, 2017, 03:39:34 PM »

I I  have seen spike similar to these on my pans . but they're spurs in th sound card  caused by the close proximity of the graphics or other pc card to the sound card? . Disconnecting the input to the sound card and the signal stays.
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K0UA
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« Reply #12 on: November 20, 2017, 03:44:04 PM »

Mine have nothing to do with any sound card or PC.  They are outside signals.
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AE5GT
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« Reply #13 on: November 20, 2017, 04:00:57 PM »

Is it just on 80M ?
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K0UA
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« Reply #14 on: November 20, 2017, 04:57:30 PM »

Is it just on 80M ?

Not mine..  All the way thru 6, but getting  very weak up there.
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