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Author Topic: Carrier Every 31khz Moving Across 80m Band  (Read 657 times)

K3YR

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Carrier Every 31khz Moving Across 80m Band
« on: November 28, 2020, 09:16:05 AM »

Hi,

My son is a youth operator and recently obtained his General ticket.  Unfortunately, he doesn't live with me; he lives about 3 miles away with his mom (my ex). 

He is running an ICOM-7300 located in the basement of a two-story house.  He has a G5RV antenna strung between the back of the house and the end of his mom's property. 

He observes strong carrier signals on the waterfall spaced approximately 31kHz apart on the 80m band - but not on 40m or 20m.  This interference appears only on 80m.  He doesn't have any problem on 40m or 20m.  But on 80m, this interference is spaced evenly at 31khz intervals and - what's worse - it drifts across the band.  So even if he chooses to work on a frequency that appears to be clear of the interference, within a few minutes the carrier will drift across his chosen frequency and render it unusable.

I'm guessing it is RFI from something in his house, or in a neighbor's house.  Actually, I'm hoping it is in my son's house, because then - once we locate the source - it will be relatively easy to fix.  But if it's coming from outside the house, it will be much harder to pinpoint the source and mitigate.

So, for the past couple of days, he and I have been trying to troubleshoot this and locate the source of the RFI.  There's a big plasma TV in the same basement room as his rig, and that was my first suspect.  So he unplugged it, but the RFI was still there.  Ditto with his Wii game unit also in the basement.  Ditto with the remote-controlled LED lights in his basement.  Unplugging these items did not eliminate the RFI.

I also suspected the monitor for his gaming PC which he has upstairs in a second-story room in the house.  He switched off the power strip, so no power going to the CPU, the PC or the attached printer.  It did not eliminate the RFI.

I also had him unplug the router for their internet/WiFi service.  No effect.

At this point, I don't really know what else to check.  They do have another TV upstairs in his mom's bedroom, and an AppleTV device.  The mom is a musician, so I suspected she might have had some guitar amp or other such device causing the problem, but he reports that none of that stuff is plugged in at the moment. 

I asked him to try unplugging those later today and report back to me.  But if it isn't either of those items, the only thing I can think of is perhap's his rig's own power supply unit, which is a Powerwerx SS-30DV.  I've got a battery, so I'm going to go over there, maybe tomorrow, to see if the RFI is still there if we operate the rig off battery power.  But I'm convinced that there is some gizmo in his house spewing RFI that I just haven't thought of. 

Any ideas?

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KC6RWI

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Re: Carrier Every 31khz Moving Across 80m Band
« Reply #1 on: November 28, 2020, 10:07:47 AM »

I have the same radio, and its annoying knowing that so many signals you seeing are not real, in a sense.
Turning off the power in the whole house is the way and then running the radio on a battery.
It probably something you have over looked so far. A power supply for an alarm, a dimmer switch, or a touch light lamp.
The door bell has a transformer that is always on, mine failed recently and I didn't guess that the smell it made was from the transformer.
I do have something that makes a pattern similar to what you mentioned, a 20 ft led light strip that changes colour, good hunting.
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WA6BJH

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Re: Carrier Every 31khz Moving Across 80m Band
« Reply #2 on: November 28, 2020, 10:08:10 AM »

I’d bet on the Powerwerx power supply.  I had one of those and I had to send it to Silicon Heaven by way of the landfill.  It worked fine for a couple of years and then started causing problems.
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W1VT

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Re: Carrier Every 31khz Moving Across 80m Band
« Reply #3 on: November 28, 2020, 10:08:28 AM »

It sounds like there is a lot of stuff in his home.  You may be better off listening on a battery powered radio,  shutting off the main breaker, and listening with the power off.  Some devices can take a while to run down the power.

Zak W1VT
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K0UA

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Re: Carrier Every 31khz Moving Across 80m Band
« Reply #4 on: November 28, 2020, 10:20:56 AM »

Rig on battery, turn off main breaker.  Turn on main but having turned off all other breakers, flip them on one by one. Someone at breaker box on cell phone, main operator observing waterfall of rig. Of course if the problem persists at main breaker turn off then problem is not is house. Don't forget to turn off all UPS's you may have.  Also don't forget that power supply to house may have this issue. Lots of "garbage" on power lines nowadays from power company with remote meter reading etc. Of course it could be in neighbors houses.  Nothing here you didn't already know, but use what ever you can of what I said. Another long term test is during an ice storm and power out over the neighborhood test rig with battery then.
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73  James K0UA

WA9AFM

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Re: Carrier Every 31khz Moving Across 80m Band
« Reply #5 on: November 28, 2020, 12:27:15 PM »

Since the RFI appears to be continuous, check appliances (fridge, freezer, furnace, etc) which run 24/7.  We had a Maytag 'Neptune' washer, although it didn't run full time, that put out enough RFI (jamming) to make the USAF proud.
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K0UA

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Re: Carrier Every 31khz Moving Across 80m Band
« Reply #6 on: November 28, 2020, 01:15:17 PM »

Since the RFI appears to be continuous, check appliances (fridge, freezer, furnace, etc) which run 24/7.  We had a Maytag 'Neptune' washer, although it didn't run full time, that put out enough RFI (jamming) to make the USAF proud.

Our LG washer makes noise when its tub is moving back and forth. It sounds on the radio just like it sounds audio frequency wise standing in front of the washer. "swish, swish".  Something to do with the direct drive computer controlled motor.
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73  James K0UA

G4AON

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Re: Carrier Every 31khz Moving Across 80m Band
« Reply #7 on: November 28, 2020, 03:25:04 PM »

One of those cheap 80m DF portable receivers could be useful.

Also check 160m to at least 6m. I suffer from 20KHz spaced spurs from a Chinese manufactured Solar River inverter at a nearby solar panel installation, which was easy to locate using a ferrite rod antenna and hand held spectrum analyser. These spurs are rock solid with no drift, but reach a measured -73dBm (S9) on an 80m dipole at 100 yards from the installation. They are weak on 160m, clean from 40m upwards but appear again on 6m.

Unfortunately the owner isn’t willing to fix the problem and our regulator (OFCOM) aren’t interested either.

73 Dave
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N6YWU

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Re: Carrier Every 31khz Moving Across 80m Band
« Reply #8 on: November 28, 2020, 03:28:45 PM »

With luck, it will be something in the house.  That you might be able to fix.  But I found a lot of those stripes in my HF spectrum only disappeared when the entire neighborhood lost power (PG&E PSPS outage).
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K3YR

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Re: Carrier Every 31khz Moving Across 80m Band
« Reply #9 on: November 30, 2020, 04:51:42 PM »

We did some troubleshooting today.  It is indeed the Powerwerx power supply.  We ran the rig on battery power and the strong signals disappeared.  We discovered some weaker RFI - that wasn't even noticeable when the Powerwerx was plugged in - but we quickly determined that was the plasma TV.

Thanks for all the help and good suggestions.
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KH6AQ

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Re: Carrier Every 31khz Moving Across 80m Band
« Reply #10 on: December 14, 2020, 11:22:15 AM »

RFI can be like peeling an onion; you remove one layer (dominant RFI source) to find another, and another below that one.
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K6AER

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Re: Carrier Every 31khz Moving Across 80m Band
« Reply #11 on: January 24, 2021, 03:02:15 PM »

most likely a switch mode power supply operating at 31 KHz.
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