Interference identification?

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jpsa
Posts: 23
Joined: Sun Nov 06, 2016 10:33 am

Interference identification?

Postby jpsa » Sat Mar 11, 2017 10:36 am

Approximately every 15 seconds, I get 3 (occasionally 1 or 2) short bursts of interference over most of the range 10 MHz - 30 MHz. (qrm1.jpg & qrm2 jpg). Looked at in more detail, the interference seems to have some kind of sub-carrier structure with a spacing of about 780 Hz (qrm3.jpg). There are small frequency ranges where the interference disappears: 13.9-14.45, 18.0-18.25, 20.9-21.55 and 24.8-25.1 MHz.

Anyone know what this is (& whether I'm likely to be able to do anything about it?!)
Attachments
qrm1.jpg
qrm1.jpg (238.07 KiB) Viewed 2483 times
qrm2.jpg
qrm2.jpg (190.62 KiB) Viewed 2483 times
qrm3.jpg
qrm3.jpg (128.11 KiB) Viewed 2483 times

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CaptainNemo
Posts: 133
Joined: Mon Jan 05, 2015 1:22 pm
Location: Genoa - Italy

Re: Interference identification?

Postby CaptainNemo » Sat Mar 11, 2017 11:16 am

The short answer is: I don't know.

In the meantime we wait for a noise "guru" to answer... since the noise seems to be "local", have you tried to unplug from main
all the electronic device you have at home? Take away all phones, tablets and so on?
If you find the answer please share with the community.

Bye
Gio

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DaveB
Posts: 132
Joined: Sun Feb 01, 2015 6:04 pm

Re: Interference identification?

Postby DaveB » Sat Mar 11, 2017 11:32 am

Interestingly the gaps in the frequency correspond to amateur radio bands plus a small guard band either side. - so someone is avoiding upsetting the amateur radio community :)

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DanubeBCL
Posts: 180
Joined: Sat Jul 02, 2016 12:39 pm

Re: Interference identification?

Postby DanubeBCL » Sat Mar 11, 2017 11:57 am

This is a typical pattern of "Homeplug Powerline" (PLC/PLT) modems. They are used in millions of European households (and elsewhere, but Europe is the leader) and transport network data (mainly internet via WLAN extenders) through the mains lines in the house. According to the latest European standards they are allowed to work with broadband signal levels up to 105 dBµV.

They are fully legal and produce interferences between 1.6 and 78 MHz within a radius of up to 400 metres and more. When they were allowed in Europe one of the argument of the lawmakers was: "Nobody needs shortwave radios any more. You can hear every radio station on the internet nowadays." Objections of several national spectrum authorities (and even the NATO!) were neglected. The lobbyists of the manufacturers were stronger.

After heavy protest of amateur radio clubs the producers agreed to notch the ham bands from the spectrum. But the latest PLC modems have such high levels that they produce intermodulation in the semiconductors of the households where they are used (power supplies, Monitors, TV ...) that partly the ham bands also are filled up with noise.

I myself am a victim of several(!) such PLC modems in the neighbourhood appr. 40 metres away from my antennas. I called the local (German) spectrum authorities several times for assistance, but they said the noise levels are absolutely within European limits. That means: Noise of up to S9+20 dB all over the shortwaves. DX-ing outside the ham bands is practically impossible. All totally legal.

73, Heinrich

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DanubeBCL
Posts: 180
Joined: Sat Jul 02, 2016 12:39 pm

Re: Interference identification?

Postby DanubeBCL » Sat Mar 11, 2017 12:32 pm

PS: From the answers in this post I see that the knowledge about PLC seems to be not very widespreed among members of this communinty. This astounds me because such interferences are every day business in urban areas (mostly in Europe, but such modems are sold elsewhere was well).
Here I post an excerpt of the current "static" notches vaild for such modems. If you have a similar noise pattern you can identify PLC modems from their noise gaps.
Note: The older standard did not notch all these frequencies, e. g. the CB band is not notched. Your neighbours can still have legally allowed older modems (legal signal levels on the mains line up to 65 dBµV) which do not notch all these frequencies.

73, Heinrich
Attachments
plc-notches.jpg
plc-notches.jpg (78.75 KiB) Viewed 2463 times

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jpsa
Posts: 23
Joined: Sun Nov 06, 2016 10:33 am

Re: Interference identification?

Postby jpsa » Sat Mar 11, 2017 2:19 pm

Oh, thank you. That makes sense: we've had a new neighbour move in recently. Looks as if I'll just have to put up with it. :(

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DanubeBCL
Posts: 180
Joined: Sat Jul 02, 2016 12:39 pm

Re: Interference identification?

Postby DanubeBCL » Sat Mar 11, 2017 4:12 pm

The only thing you can do is to talk friendly to your neighbour and explain your hobby to him. He can easily distribute the internet in his house with other technologies like LAN cable or WLAN repeaters not based on powerline.
In my case all talks were useless. I have nine neighbours in the meantime using that stuff. My calling of the authorities was a shot in my own knee: After the officers explained to my "hardest" neighbour that he is doing absolutely nothing wrong and his modems are fully legal he only grins at me when I try to speak about my hobby being made impossible by his PLCs.
But he is only one of nine...
73, Heinrich

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13dka
Posts: 136
Joined: Sun Feb 14, 2016 8:40 am

Re: Interference identification?

Postby 13dka » Sun Mar 12, 2017 3:08 am

jpsa wrote:Oh, thank you. That makes sense: we've had a new neighbour move in recently. Looks as if I'll just have to put up with it. :(


I think what you see there on the screenshots (thanks for them, nice examples I may refer to in future discussions!) is an idling PLC modem. In other words, it could get more nasty if there's actually data being transferred.

I don't know where you are and whatever e.g. the FCC's stance on PLC interference is, but my advice would be to never wield the "I'll call the authorities" hammer unless it's a) possible to do that and there's b) no other option left. Instead, I'd try to approach the neighbors in the most diplomatic way possible, more in a way of "Sorry to disturb you, I know you couldn't know better and it's not your fault but these devices are destroying my hobby and the considerable investments I made for it, would you be so kind to let us check for an alternative at some point, I'd reimburse you for any expenses involved!" Of course actually paying for some WLAN repeaters and gear hurts and it might be impossible if you have multiple neighbors using PLC, but it's probably more promising than trying to make them feel like they did anything wrong or stupid and laying the ground for a long-term neighborhood fight.

As for the "authorities" option, I live in Germany like DanubeBCL and if you're not a licensed ham they do squat about it, IOW they refuse to even come and make measurements for some reason, as if SWLs are not belonging into the group of "radio amateurs", as if PLC interference had anything to do with a permission to transmit. So we have absolutely nothing to back any claims then, even if the devices are not complying with the regulations. All you can do is asking for your neighbors understanding and explain with as few and simple words as possible what the interference means for your hobby, which will appear strange enough to them anyway.

The only (stupid) things I can think of that would give some of them a bit of additional motivation would be "privacy/security". After all PLC is (possibly, don't know, maybe not) even less secure than WLAN and they are making big antennas out of their houses, with a possible range far beyond WLAN. Some may buy the "electrosmog" scare, as they may not know that RF radiation is involved in that technology. AFAIK some of these devices even advertise with a "no WLAN radiation" sales pitch, targeting those people.

It's all pretty devastating for all parties involved. For example, for the first time in my life I have a chance to (permanently) put up some serviceable antennas and really enjoy this hobby and so I consider shelling out big $$$$ for e.g. an IC-R8600 sometimes, but given the possibility that such a crappy little device could come online again any minute and make that a really pricey paperweight (at least for shortwave) I just can't do that. So that's yet another loss for the industry too. The argument "nobody needs shortwave anymore" is just as untrue as it is stupid, it's like saying "nobody needs to see stars anymore, including your kids" to help an industry selling more, particularly stupid light bulbs. The radio spectrum is a natural resource that belongs to everyone just like the starlight on the other end of the spectrum it and deserves protection. But of course neither end of the electromagnetic spectrum gets that protection, not even when academic interests are involved, but those get at least sometimes funding to put up optical and radio telescopes at still worthwhile, extremely remote places. Schools wanting to participate in one of the (radio-) astronomy projects specifically made for schools do not, and if the spectrum is so polluted in their neighborhood that won't happen in first place or it will be a desaster, meaning less future astronomers and kids coming to the conclusion that yet another aspect of nature cannot be observed anymore because adults are greedy b...ards turning everything into s..t.... [/rant]

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DanubeBCL
Posts: 180
Joined: Sat Jul 02, 2016 12:39 pm

Re: Interference identification?

Postby DanubeBCL » Sun Mar 12, 2017 9:38 am

Yes, PLC is working with on demand modulation. That means that idle PLC modems indeed make less noise. When data is transferred the modulation changes amplitudes rhythmically from almoust null to full within milliseconds. This is an obstacle when you want to null-phase the interference with a noise cancellor (phaser) using two antennas. The short pulses of the PLC modulation do not allow to adjust your noise cancellor properly. It takes you minutes to find a suitable phase and amplitude setting. I always wish that my neighbours do video streaming with their PLCs. Then the interference is constantly on a high level and I have more time to null-phase the interference.

But noise cancelling is useless when more than one neighbour is "on". And this is meanwhile standard. As I said: I have nine neighbours with PLC! And they are on the internet night and day! I did not believe that people are such internet addictet.

BTW: PLC is also used for communication in so called "smart homes" and distribution of video signals from satellite dishes on the roof into the house. And I am afraid the future will bring more applications.

PLC is the end of shortwave communication between 1.6 and 78 MHz. And the manufacturers cannot wait to see the end of FM radio to take over the spectrum up to 200 MHz. It is a complete nonsense to use power lines for RF signal transport. This is what the officers of my spectrum supervisor also said. But they also said that they are helpless as the law explicitely allows such interference at high levels.

73, Heinrich

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CaptainNemo
Posts: 133
Joined: Mon Jan 05, 2015 1:22 pm
Location: Genoa - Italy

Re: Interference identification?

Postby CaptainNemo » Sun Mar 12, 2017 11:03 am

If I understand well, jpsa posted an image of an idle modem,
in other words those horizontal lines are a sort of hearthbeat to keep in synch the system.

Can anyone share here an image of a full operating modem? I mean, when there is data traffic?

Thanks in advance.
Gio.

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