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Author Topic: Interactive RFI?  (Read 339 times)

AD0AR

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Interactive RFI?
« on: February 13, 2021, 04:34:05 PM »

Has anyone ever observed interactive RFI? 
I have the 20 meter band blanketed by soft, white noise, but if I transmit any carrier higher than 2 watts, the RFI is gone when my radio switches back to RX for about a second, then the noise floor returns to s9+.  I can hear perfectly weak stations for this moment of silence before the noise comes crashing back in. 
  I pulled the breaker on the qth and ran on battery power with no difference.  I walked around the neighborhood with my R20 handheld receiver and I do not observe any abnormal noise peaks.
One other thing-  This only happens during the day.  Right around sunset it suddenly stops.
  This one has me stumped folks. 
Anybody else seen anything like this?
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KF5LJW

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Re: Interactive RFI?
« Reply #1 on: February 13, 2021, 04:42:54 PM »

Say helllo to solar power.
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AD0AR

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Re: Interactive RFI?
« Reply #2 on: February 13, 2021, 05:47:24 PM »

It's ironic you say that as my antenna is over my solar array.  I even unplugged that so I know it isn't that and none of my neighbors have solar in this corn field I live in so I don't have a clue where the RFI is coming from.
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KD6VXI

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Re: Interactive RFI?
« Reply #3 on: February 13, 2021, 06:19:35 PM »

If you have optimizers or micro inverters they are powered by the individual panels they attach to.

This could be your problem.  Even with the breaker or main inverter off the micros or optimizers will still run.  They don't put voltage out (in the case of micros) but the internals are working looking for 240 to sync to.

And in the case of optimizers they are doing their job 100 pct in almost all cases looking for an inverter.

Having an antenna anywhere near a solar system is a recipe for disaster.

Get the antenna as far away as possible and common mode choke the crap out of your coax, both at the antenna feed point and the point the coax enters the house.  Which will probably not do much....

--Shane
KD6VXI
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W4MDP

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Re: Interactive RFI?
« Reply #4 on: February 13, 2021, 09:25:54 PM »

About 5 years ago I put in solar.  All of a sudden I had no signals on 20m.  Actually after testing I found broadband noise from about 14 MHz through about 22 MHz  - only during the day.  I shut down  the solar system one day and, voila!! HF signals  again.  Solar City (Mr. Musk)
was called and after some Q and A with me they told me someone would be out to check.  They did a day long analysis and ended up replacing most of the wiring an some of the mini inverters on my 25 panels.  Since that day my system has been clear of problems ---except now there are many more solar systems in the neighborhood and I can see the noise level starting to rise again.
Check around your neighborhood for new solar.  It is very difficult to trace because it is primarily broadband noise that you can't always see on a spectrum analyzer  bur youy can hear it beating against on frequemcy QSOs on the air.
73
Mark
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AD0AR

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Re: Interactive RFI?
« Reply #5 on: February 14, 2021, 03:44:09 AM »

Folks, it's not my panels.  I don't understand when I said I disconnected it, I did.  I designed it.  It is in a zero power state.  It is not the panels.  What part of unplugged don't you understand?  I have a foot of snow on my panels so not a problem to pull the plug on something that isn't being used. No inverters.  Just a bank of 12 AGM batteries and a charge controller.  The batteries reside inside my basement with a disconnect there.  The charge controller is in a zero power state.
Nobody else has solar in my association, and if they did, it would be under a foot of snow. 
It is not solar causing it. 
I wonder what else could be causing it?  When the noise starts back up, it sounds like a motor starting, then achieves a white noise like noise in less than a second. 
Bizarre behavior, but I do admit that if it is interfering with my radio ops and is that sensitive to RF, I can find comfort that I am interfering with its operation too.
  If I were to take an educated guess, I would say it is a commercial appliance found on the second floor of a house that is most likely residing in one of the adjacent houses.  I just don't know what.
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W9IQ

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Re: Interactive RFI?
« Reply #6 on: February 14, 2021, 05:38:29 AM »

If I were to take an educated guess, I would say it is a commercial appliance found on the second floor of a house that is most likely residing in one of the adjacent houses.  I just don't know what.

A commercial appliance that stops working, or at least interfering, after dusk? That is hard to envision - what do you have in mind?

The micro inverter pod on the back of a solar panel works with very little irradiation so I would expect that it is powered even under a foot of snow. So while you may not have any on your panels, it could be that there are others in the neighborhood. Keep a log of the time at which the interference starts and stops. The rapidly changing sunlight conditions this time of year helps to correlate potential diurnal sources.

Have you added any appliances or lamps to your QTH recently? Perhaps a new security light? Has the city or association done any LED upgrades recently? We see more of these as RFI sources in recent years.

Is there any construction in the area? Some of the LED informational signs have solar panels for charging their batteries.

When shutting off breakers, don't forget about the battery backed up devices - notebook computer, UPS, cable/fiber modem, alarm system, smoke alarm, etc.

- Glenn W9IQ
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- Glenn W9IQ

God runs electromagnetics on Monday, Wednesday and Friday by the wave theory and the devil runs it on Tuesday, Thursday and Saturday by the Quantum theory.

AD0AR

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Re: Interactive RFI?
« Reply #7 on: February 14, 2021, 06:25:59 AM »

Thanks for your insight Glenn.  I'm starting to think it is something much farther away than a neighbor's residence. 
  Even with -8F temperatures here, I conducted a thorough walkaround in my cornfield surrounded subdivision with my Icom R20 and noticed a even, high noise floor that did not vary much. 
  No utility poles here.  All infrastructure is buried. 
 I will have to drive around and see if I can better locate the source.
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AJ8MH

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Re: Interactive RFI?
« Reply #8 on: February 14, 2021, 07:31:23 AM »

but if I transmit any carrier higher than 2 watts, the RFI is gone when my radio switches back to RX for about a second, then the noise floor returns to s9+

The noise source must be very close for your 2 watt carrier to shut it down.  With an S9+ signal, your R20 should easily hear it, too.

Could it be something in your loop being affected by outside temperature variations? When does the noise start? Is it at sunrise or within a hour of sunrise.
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W9IQ

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Re: Interactive RFI?
« Reply #9 on: February 14, 2021, 08:08:04 AM »

I agree with Joe's assessment regarding power level.

One other thing that we have run into is automatic meter reading infrastructure for energy and water utilities. These typically use RF links for back-hauling the data to the utility. Perhaps one of these nodes has developed a problem. Look for the poles that feeds your buried power lines to see if you can spot a box with a small yagi or dish antenna attached.

- Glenn W9IQ
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- Glenn W9IQ

God runs electromagnetics on Monday, Wednesday and Friday by the wave theory and the devil runs it on Tuesday, Thursday and Saturday by the Quantum theory.

K6AER

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Re: Interactive RFI?
« Reply #10 on: February 14, 2021, 08:54:08 AM »

Check your power meter. The new ones can be read from the central office. Shutting down the main breaker will not turn off the power meter. They operate in the HF band.
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AD0AR

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Re: Interactive RFI?
« Reply #11 on: February 14, 2021, 09:42:20 AM »

Other than being real cold here (-10f) No changes have occurred.  Buried utilities and they are making some changes to the infrastructure by burying more and more but I would think they would not be an issue due to the distance (more than 1500ft)
I'm starting to think it might be a neighbor with one of them electronic battery maintainers on one of their unused vehicles.
I'll ask around.
 
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KH6AQ

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Re: Interactive RFI?
« Reply #12 on: February 22, 2021, 08:15:28 AM »

Using the R20 receiver have you confirmed the noise, transmit, no noise, noise sequence?
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WA8NVW

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Re: Interactive RFI?
« Reply #13 on: February 23, 2021, 05:02:11 PM »

This could also be caused by a neighbor's cheap solar-powered LED security light (Harbor Freight or similar) or by some decorative LEDs atop fence posts.  Sounds like the charger shuts down when it "hears" RF, then restarts when it detects enough voltage coming from the panel to charge the battery which is in the lamp head.  Charger board goes to sleep when the solar panel voltage drops too low, then after prolonged dark period it turns on the LED lamps. 
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AD0AR

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Re: Interactive RFI?
« Reply #14 on: February 23, 2021, 06:48:45 PM »

Found the source.  Neighbor had a Promariner Pro Sport 12 trickle charger on his bass boat trolling motor batteries.  Not solar. Not LED. Just a old fashioned fanless (looks like a car stereo amp) potted dual battery charger.
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