Broadband HF interference

[majoco]

Hi Guys - I have been plagued by this broadband noise for about 4 months now. I've done all the usual tricks, turning everything off, walking around outside with a portable but no luck in finding a point source - it seems to be everywhere. I don't think we have cable television and if we did, I don't think it would be on HF frequencies. It certainly makes all the low level signals on the 31, 30 and 25m bands pretty hard to resolve. The pattern doesn't really change day or night, week in, week out. It sounds just like white noise but you can see at the 8MHz picture that it has some 'structure'. The 12MHz pic shows how sharply it drops off so it's certainly not a natural phenomenon. I live in a fairly low-noise but low-signal area so this rather spoils all my to get the best results from my gear. Any help gratefully received.

 

[K4EET]

Martin,

Is the "noise" consistently centered on the same frequency 24/7 or does it move around?

Due to your proximity to certain countries, I'm wondering if it is a jamming signal blocking out free-world broadcasts to those countries?

73, Dave K4EET

 

[majoco]

Hi Dave, no, it never moves. I'll go for a walk around the neighbourhood with a portable and see if it's all over the village or just very local.

 

[ka3jjz]

When you do your walk with your portable, if it has one, don't extend the whip. And if you can reduce your RF gain or use an attenuator, do so to the point where you can just hear the receiver's background noise (all radios have it, it can take effort to recognize it). That way if you approach a noise source, you should obviously hear the noise increase, assuming the radio's AGC doesn't get in the way.

Make sure your hands aren't sweaty; skin condensation will cause it to act as a very crude antenna in some cases. A light glove may be necessary.

Mike

 

[majoco]

Well, I've walked around the village and the noise signal is everywhere. Most of our services are underground, there are some instance where a power pole has lines going to a few houses and there are telephone junction boxes every few yards. This is where the noise was greatest but it never reduced to zero anywhere.

So back home to experiment. Turned off all the power at the incoming meter panel. Ran the G33 off a GelCel and the HP laptop - no change in noise signal. I only have three accessible phone jacks, one for an answerphone, one for a master wireless telephone with two remotes and my desktop WiFi router. Of course the desktop and router aren't going with no power. Pulled the plugs from the phone jacks and the noise level dropped marginally, about 3dB lower than indicated in the above screenshot - so the signal is being radiated from my house wiring. Once upon a time you could short out the phone pair and pull in the line hold relay at the exchange but I don't think it works like that now....

So I think I'm stuck with it. There is an Intruder Alert/Monitoring Service in our national amateur radio association so I might send the pics and text to them to see if this is a common occurrence.

 

[prcguy]

In some areas of the US we have broadband over power lines for Internet service, which can wreak segments of the HF band. Do you have such services in NZ?

 

[iMONITOR]

In some areas of the US we have broadband over power lines for Internet service, which can wreak segments of the HF band. Do you have such services in NZ?

Does that apply to Smart Meters as well? Not sure what frequency they operate on, or if they're over the air or over the power lines.

 

[krokus]

Pulled the plugs from the phone jacks and the noise level dropped marginally, about 3dB lower than indicated in the above screenshot - so the signal is being radiated from my house wiring.

Do you think the signal is coming in from off site? If so, disconnect your telephone network interface. (It sounds like you should know what that is.)

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[Boombox]

I have no idea what your RFI problem is.

But the one time I dealt with really strange RFI, which sounded like aliens attacking, it was some family's new washing machine, and it radiated from their house, to the powerlines, and the powerlines radiated it for a block, acting as antennae.

I would hazard a guess that even though your power is mostly underground, those power cables are still carrying a form of RFI, and the poles that carry it above ground -- and the power wires coming off those poles -- are radiating what is already being carried on the underground power lines.

I know this is stating the obvious here, but your problem must be somewhere in the vicinity, either coming from a business or someone's house, and their RFI is going through the power system. The fact your wiring is underground probably just makes tracking it worse. With overhead lines, like I have here, it was fairly simple.

Ironically, the noise went away for the most part, when the family split. The dude lives alone now, and obviously he doesn't do as much laundry living alone.

 

[majoco]

I'm sure that it's not coming down the power lines, because I can change the character of the bands in the 8MHz sector by plugging in or out any of the phones or my router. Also when walking around the village, the interference signal was strongest at the phone junction boxes, not the power poles.
As far as I know there is no BPL in NZ - the ham radio magazine would have kicked up large by now if there was.
Next time I see the phone company van down by their building I'll take my radio and go and have a chat to them, until then I may just have to put up with it - I can still receiver the other band well enough.

I too have interference from the washing machine and the dishwasher so now I tend to put them on when I'm not home! The washing machine especially - it's one of those direct drive motors that use a chopped DC to vary the speeds and direction of the drum.

Thanks for all your inputs.

 

[ka3jjz]

I didn't ever think there would be a list server for RFI, but sure enough, here it is...

RFI Info Page

Mike

 

[w2xq]

Mike, that RFI website is a moldy old design. Sure enough, I see the archives date back to 1998. :/

 

[ka3jjz]

It's not really a website per se - that is the mailman type list server screen. And to your point about how far it goes back- I have one question

So?

The latest archive is this month, so this must be a pretty active reflector. Personally I think it's worth looking at, but of course, YMMV....Mike

 

[w2xq]

Geez, Mike... it was a joke.

 

[majoco]

Interesting. I have made a subscription to that list and I'll read some of the posts just to see what their major topics are. I suspect that anything that crops up in NZ will only be specific to here, rather than a word-wide phenomenon.

 

[ka3jjz]

Geez, Mike... it was a joke.

which came out wrong on my end. I was trying - not well - to let folks know about the Mailman software. It is very simplistic but for some it works just as well. My bad

Mike

 

[krokus]

I'm sure that it's not coming down the power lines, because I can change the character of the bands in the 8MHz sector by plugging in or out any of the phones or my router. Also when walking around the village, the interference signal was strongest at the phone junction boxes, not the power poles.
As far as I know there is no BPL in NZ - the ham radio magazine would have kicked up large by now if there was.

What about remote monitoring/control of substations or switches? We do have somr of that in the US, and I doubt we are the only ones.

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[majoco]

Yes, we do and they're all up in the 400MHz range - they don't transmit continuously over a 3MHz+ bandwidth in the HF spectrum.