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N0JCG
join:2003-07-18
Minneapolis, MN
| reply to TACSPEED
Re: You've got to be kidding me
said by TACSPEED  :
quote:
The key is to keep the intensity of the RFI low enough as to not cause RFI problems with the majority of the people or to interfere in a frequency spectrum that's not occupied.
Exactly! Which is why the 5GHz UNII band is the place for this stuff! 5GHz permits interference management through geography. | |
W1RFI
join:2003-05-12
Burlington, CT
| reply to TACSPEED
The interference you describe from power lines is not legally acceptable. The FCC has written advisory notices to over 30 power companies to date, requiring that they correct the harmful interference from their power lines.
ARRL has a cooperative agreement with the FCC to try to resolve these cases directly with the power companies, but after those reasonable efforts fail, the FCC is willing to start waving the stick.
See:
»www.arrl.org/tis/info/part15.html
for information about the FCC Part 15 regulations.
Ed Hare, W1RFI
ARRL Laboratory Manager | |
jacour
join:2001-12-11
Ypsilanti, MI
 ·Comcast
| reply to RoguePimp
There is a way to fix this problem, and that is to design a power grid that will contain the signal and not radiate the signal. That is how cable systems work, and that is why all CATV uses coaxial cable with an outer shield. The problem is that the power grid was not designed with BPL in mind and as it sits, it acts as a huge antenna.
The problem for the power companies is that if they are forced to shield their installation, the cost would be so high as to make the price of the service non-competitive. It would be much cheaper to string coax to customers that don't have cable service than to retrofit the power grid.
This is not just a regulatory issue - this is where physics meets up with economics. Ultimately it comes down to a public policy decision on whether to wipe out 80 MHz of HF radio spectrum to benefit those users in rural areas that do not have access to DSL or cable. While the rural users might have a need for speed, this may just be a red herring to get regulatory approval; I don't see the tests being done in rural areas. | |
W1RFI
join:2003-05-12
Burlington, CT
| reply to RoguePimp
> They are joking right? Who does not have a complaint
> about BPL? There must be a way to work out the issues
> at hand.
With BPL, that might be very difficult. And it is moot, because rather than addressing the interference problems head on, as did the cable industry, the DSL industry and industry consortiums like the Home Phone Networking Alliance, the BPL industry has taken the firm position that BPL cannot and will not cause interference to radio services. It is not possible to work with anyone on a problem they claim doesn't exist.
> I refuse to believe that with the state of our
> technology we can't work on a way to avoid
> interference. I just don't but it that all of the
> problems can be so bad.
The solutions to BPL interference would require that BPL radiated noise be from 1,000 to 1,000,000 times (30 to 60 dB)less than the present FCC limits for unlicensed emitters. That is a lot of supression to achieve on a regular basis. Studies done by ARRL and the British Broadcasting Corporation demonstrate that 60 dB of supression would be required to prevent most -- but not all- levels of interference. And a 30-dB reduction in BPL signal levels would virtually mean that BPL can't work, because the BPL manufacturers have been very clear in their comments to the FCC that their systems have to operate at higher levels than the present levels of man-made noise on power lines.
As to how bad, in the US, BPL would be permitted a radiated emission of 30 uV/m 30 meters from the source. If you put a typical shortwave antenna in a 30 uV/m field, the received noise level will be very strong, S9+ by receivier "S" unit conventions. This is about 1,000,000 times stronger than the weakest signal that could normally be copied by that station. ARRL and others have verified this by 3 or 4 different calculation methods.
Most of the BPL marketing trials are small, at least in the US -- from 10 to a couple of hundred homes. Because there were virtually no amateurs in these trials, ARRL did the second best thing and brought an amateur station to the trial areas. The interference was just as predicted, and it would have been apparent to even an untrained observer that radio reception was being degraded significantly. ARRL and a number of European amateur societies have documented this effectively on the video recordings at »www.arrl.org/tis/info/HTML/plc#video.
> After all, I get my High speed cable through the same
> line as my digital cable in the house and I do not get
> any interference.
Inside that cable -- a well-shielded environment -- the modem and TV channels all use their own frequencies, separate from each other. They are able to be separated the same way that you can have multiple TV channels inside the cable, each uniquely tuned by your TV set or set-top converter.
BPL will not be the only device that has emissions at the FCC Part 15 limits. As an amateur operator, I can hear "birdies" from my neighbors' computer systems. A few are strong, but I can easily move frequency a bit and avoid them. Such devices generally have a local interference potential, so I am not apt to hear one from a mile away.
That may not always be true, however. A few years back, an early version of wireless modem jacks operated on 3.53 MHz. Like BPL, they were carrier current devices that operated at the FCC limits. They were purchased in volume by TCI Cablevision to use with their digital cable TV installations. Very soon, there were hundreds of reports of harmful interference. In some areas, the lower portion of the 3.5 MHz amateur allocation was blanketed with dozens of signals. Ultimately, AT&T Broadband, who had purchased TCI, did a system-wide recall of these devices. The manufacturer acted responsibly and redesigned the product to use a different frequency, but someone's ox was getting gored.
Phase II of that problem represents a different ox. Aeronautical, Inc operates 4 aeronautical HF communications centers. In their California facility, they were getting interference on 3.013 MHz. They contacted the FCC, who tracked it down to a number of devices in a nearby neighborhood, but they were unable to pinpoint the exact source because the power lines were radiating the signal everywhere. AIRINC had to abandon the use of that frequency at that facility.
These are some pretty serious problems from carrier-current devices that operate at the FCC limits. Both operated on a single frequency and were intended to be used on residentail and business electrical wiring -- ostensibly a localized interference potential. But both caused some pretty serious problems.
Now, take that same "legal" level and operate it on entire swaths of spectrum. Operate it 24 hours a day. And build it as big as an entire community. That's BPL.
The best analogy I can think of is airplanes. We all hear the occasional small plane that flies overhead, making more noise than we would like. We don't like it, but we live with it. Now, could we live with the same level if it were flying around the house 24 hours a day? Could our society live with the same level if every town had dozens and dozens of such planes flying everywhere all the time?
I think that FEMA has it exactly right when it says that the benefits of BPL -- and there are benefits -- do not outweigh the harm to virtually losing a unique and valuable international resource -- shortwave communications. In those areas where BPL is deployed and on any spectrum BPL uses, if it operates at the FCC Part 15 limits, nearby radio communication will be degraded to the point of unusability. ARRL and Amateur Radio are concerned; FEMA is concerned; the ITU is concerned; the BBC is concerned, and in many countries where the regulators have taken a close look at the impact, the decision was reached not to permit BPL operation.
ARRL's information and links on BPL is well worth the read. See »www.arrl.org/bpl and follow the links. I have recent information about official interference reports and official reguator decisions in Europe that I hope to get onto the page this week. A few of the links appear to be busted, so try the page in a few days as I figure out the new URLs.
Ed Hare, W1RFI@arrl.org
ARRL Laboratory Manager | |
91439306
15,000 Watts of Bass Power
join:2002-10-16
New Milford, CT
| reply to W1RFI
said by W1RFI :
The interference you describe from power lines is not legally acceptable. The FCC has written advisory notices to over 30 power companies to date, requiring that they correct the harmful interference from their power lines.
ARRL has a cooperative agreement with the FCC to try to resolve these cases directly with the power companies, but after those reasonable efforts fail, the FCC is willing to start waving the stick.
See:
»www.arrl.org/tis/info/part15.html
for information about the FCC Part 15 regulations.
Ed Hare, W1RFI
ARRL Laboratory Manager
I would like to see them correct the severe RFI from the new traffic signal lights (LED) used in CT now. When I'm 1/4 mile or less from one of those things, it buzzes louder than the audio of the AM station I'm trying to hear.
Who the heck approved these solid state traffic lights without RFI testing first? They would have put in filtering had they bothered to test them before deploying thousands around here.
--
Take care,
Mark & Mary Ann Weiss
Hear my Kurzweil Creations at: »www.dv-clips.com/theater.htm
Business sites at:
'»www.dv-clips.com
'»www.mwcomms.com
'»www.adventuresinanimemusic.com
| |
TheMadSwede
Premium
join:2001-01-30
Holland, MI
·Charter Pipeline
| I hate to turn this into an "interference annoyance" forum, but I live less than a mile from an FM tower for a local station and it jacks with at least 2 other stations that I enjoy.
--
Hey - there's this thing called spell check... | |
N0JCG
join:2003-07-18
Minneapolis, MN | Have you filed a complaint? | |
rf_engineer
join:2003-08-04
USA
| reply to TheMadSwede
said by TheMadSwede :
I hate to turn this into an "interference annoyance" forum, but I live less than a mile from an FM tower for a local station and it jacks with at least 2 other stations that I enjoy.
It may be an issue with your receiver. A lot of pieces of consumer equipment can't deal with strong signals nearby, especially if they fall on the right frequency (aka the "IF image frequency") or are adjacent to a distant station you're trying to receive. So this may not be the fault of the local FM station. You should probably start by talking to the chief engineer of the station and give specifics. They don't like FCC compliants and should be willing to help or at least figure out what's really going on. | |
W1RFI
join:2003-05-12
Burlington, CT
| reply to TACSPEED
> Learning from the failures of Nor.Web approach, second
> generation PLC technologies are using techniques like
> OFDM, which substantially reduce the potential of
> interference to radio users, thanks to a decrease in
> transmitted power spectral density.
OFDM does not decrease the transmitted power spectral density. It takes a certain amount of spectrum to transmit a certain data rate at any specific signal to noise ratio. In the US, the OFDM BPL systems operate at the FCC Part 15 radiated-emissions limits of 30 uV/m at 30 meters, just like other BPL systems.
Go to the ARRL video at »www.arrl.org/tis/info/HTML/plc#video and look at trial area #4, the Ambient BPL system in Briarcliff Manor, NY. It is an OFDM system based on the DS-2 chipset. That will demonstrate quite well that OFDM does not reduce the inteference potential. 30 uV/m is 30 uV/m is 30 uV/m when it comes to interference and the simple laws of antenna physics predict what signal levels will be received on nearby antennas.
Ed Hare, W1RFI
ARRL Lab | |
91439306
15,000 Watts of Bass Power
join:2002-10-16
New Milford, CT
| reply to TheMadSwede
I live within the fall zone of a 50,000-watt FM tower, and ya know what? Not a damned thing anyone can do about it. They were here since 1959 and the houses came in the 1960s.
It is called 'blanketing' interference and radio receivers have to accept it.
It wipes out the ENTIRE FM dial up here, on my Jensen car stereo, and most of the dial on the wife's Sansui. Forget about using a portable or clock radio. 100% obliteration.
Not a damned thing anyone can do about it.
--
Take care,
Mark & Mary Ann Weiss
Hear my Kurzweil Creations at: »www.dv-clips.com/theater.htm
Business sites at:
'»www.dv-clips.com
'»www.mwcomms.com
'»www.adventuresinanimemusic.com
| |
rf_engineer
join:2003-08-04
USA
1 edit | said by 91439306 :
It is called 'blanketing' interference and radio receivers have to accept it.
It wipes out the ENTIRE FM dial up here, on my Jensen car stereo, and most of the dial on the wife's Sansui. Forget about using a portable or clock radio. 100% obliteration.
Realize, though, that it's not necessarily the fault of the radio station. Every receiver contains a filter in the "front end", the first part of the receiver that gets the signal from the antenna. The job of this filter is to attenuate signals that we aren't interested in receiving. A perfect filter would infinitely attenuate unwanted signals. In the real world, though, a front end filter attenuates the unwanted signals a large amount, but some of the unwanted signal gets through the filter. Taken to the extreme, when you have a powerful transmitter next to a receiver, a large amount of unwanted signal will get through. This unwanted signal gets to subsequent stages and gets detected and converted to audio.
Better receivers have better filters and will be able to tolerate strong signals, especially ones that are adjacent or close by your intended receive frequency. One could also put a "notch filter" ( »www.scott-inc.com/html/fmnotch.htm ) in front of the receiver to add additional attenuation to the unwanted signal.
quote:
Not a damned thing anyone can do about it.
Actually, FM stations are required to help resolve blanketing issues in some situations »www.current.org/pb405.html and »www.scott-inc.com/html/73318.htm ...
( Update: Ooops, I didn't see the dates in your post. Buy a notch filter  ) | |
91439306
15,000 Watts of Bass Power
join:2002-10-16
New Milford, CT
| I hung a 1/4-wave shunt across the 300 ohm terminals of the Sansui, and that brought in at least the 5 big CT stations, but I find it unreasonable that a 50,000 watt FM with a tall E-plane pattern is allowed in a residential neighborhood. We didn't have this problem when they used 6 bays of Dialectric antennas. But now that they increased power and decrease to two bays of ERI antennas, we have a 20X increase in ground level field strength.
--
Take care,
Mark & Mary Ann Weiss
Hear my Kurzweil Creations at: »www.dv-clips.com/theater.htm
Business sites at:
'»www.dv-clips.com
'»www.mwcomms.com
'»www.adventuresinanimemusic.com
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