BPL: No Shortage of Critics
So is 5Ghz the answer?
by N0JCG 11:17AM Tuesday Dec 30 2003 Tipped by Karl Bode
Amrad (the Amateur Radio Research and Development Corporation) is the latest group to respond to the FCC's request for feedback on broadband via power-line technology. The group, like others before them, notes there will be a serious impact on radio communications if the technology becomes widespread. Unlike others, AMRAD offers up some suggestions on how to minimize the potential impact of BPL (broadband via power-lines) in their submission
(pdf file) to the FCC.
The group conducted a RF Susceptibility experiment this past November on the Potomac BPL trial being conducted by Potomac Electric Power Company (PEPCO). Unlike previous reports that emphasize BPL's impact on radio operators and emergency communications, AMRAD also emphasizes the reverse. "From this test data, it is apparent that radio amateur operations in the test neighborhood could cause many homes to lose their Internet connection during the times when the radio amateur is transmitting,"
the report notes.
The report offers some suggestions on how to reduce interference, including replacing unshielded Romex with commercially used BX armored cable and metal outlet boxes - something the report notes is more practically performed during construction than at a later date. The report also recommends the use of quarter-wave coaxial stubs at the wall plug to absorb energy at the interfering frequency.
The BPL technology used by PEPCO comes from Current Technologies, and is one of several technologies that create significant interference problems to HF and low-VHF spectrum use between 2 and 80 MHz. Such interference problems have been the reason (along side significant cost) that a great number of BPL trials world-wide have run into trouble
. The concerns about interference haven't been enough to slow many projects in the States, like the goal of wiring the entire city of Manassas, Virginia
There are some alternative BPL technologies under development, that operate primarily within the unlicensed 5 GHz ISM band. One version of the technology being developed by Corridor systems uses 216mbps capable BPL up to a point, and then connects to the end user via 802.11 wireless gear (see pdf
of Corridor's BPL specs). Such BPL alternatives are currently being tested by California PG&E. However there are several technologies that either currently use, or plan to use the 5GHZ band (like 802.11a or the looming 802.11n
) - so the interference battle may simply change battlefields.
59 comments .. click to read
|reply to bmn |
Re: Solution is worse than the problem...
said by bmn:
said by rf_engineer:Actually, I was never really "pro-BPL" due to the interference issues. My concern is less with HAM and with more mission critical devices and uses of the impacted frequencies. However, I don't think moving the interference issues to another spectrum (5ghz) and one that is going to be heavily used is a solution. A solution would be to find a range that is vacant and use it.
It's funny though how everyone is for BPL until it comes into their radio spectrum neighborhood. Not in my backyard, you say ?
Good point, but that's the kicker, finding vacant spectrum. If BPL interests actually tried to get a real 80 Mhz wide allocation in HF/VHF, they'd be laughed out of Washington. I have often said before that we could perhaps look for a 1 Mhz chunk for BPL. This would be able to support the drops to houses at maybe a 500 kbs rate, but wouldn't be sufficient for the main backhaul. But 2.4 and 5 Ghz is just so much better suited for this, either as a wireless medium or surface propagated on the line (like Corridor). Part 15 rules in the HF band where never meant to support wideband uses in a large geographical area like BPL. On the contrary, it was to support small narrowband consumer devices that occasionally transmit and at most would be a minor occasional nuisance to licensed users in the band. Part 15 in 2.4 and 5 Ghz land, though, allows much higher radiated power levels. This is why the band is ideal for unlicensed WISP use. Also, the 5 Ghz band is also known as UNII or the Unlicensed National Information Infrastructure band, created during the Clinton/Gore administration. It was created and built from the ground up with such applications in mind, and it was recently expanded. BPL type applications really belong there, not in worldwide communications spectrum. But good luck getting a free and clear 80 Mhz chunk in any microwave bands.
Another thing to consider is that comparing the interference issues in the HF spectrum versus the interference that would be present to incumbent users at 5 Ghz is like comparing apples and oranges. Current devices at 5 Ghz are much like wideband spread spectrum or OFDM BPL devices. HF on the other hand is typically narrowband uses with very sensitive receivers. 5 Ghz can't propagate across the globe like HF, therefore interference effects are very localized. It's also much easier to create highly directional antennas to avoid interference, such as in a WISP or WLAN application. HF directional antennas with the equivalent directionality are measured in acres or even square miles !
The mission criticality that you refer to is really in the eye of the beholder. Many Internet citizens consider 2.4 and 5 Ghz "mission critical" because they're aware of it and use it, as do WISPs. HF radio spectrum is "mission critical" for several government services and international entities. Even truckers would consider 27 Mhz (CB) mission critical when trying to get directions in an unfamiliar town, or calling for emergency help. You'll find that most any chunk of spectrum has users which depend on it, so don't dismiss Ham or HF use in general as not being mission critical.
BTW, "Ham" is not an acronym so it's not really proper to refer to it as "HAM"
Long Beach, NY
|reply to cmaenginsb1 |
Re: This makes no difference
Some salient points here.
Why is BPL being pushed? Not so much because it is the best technology to get high speed data communication to the masses but because the power companies can push it as a way to create more business for themselves by jumping into this hot-technology field with as little cost or system upgrading as possible.
On the surface, who would argue with low-cost broadband access to all. But, the costs of an ineffective or problematic system needs to be evaluated. This article looks at the damage to (and from) amateur radio. Again, on the surface, most folks could care less- but amateur radio is a MAJOR communications backbone for national defense, disasters, etc.
The disruption of communications for amateur radio are also problems in many radio communication systems currently used in defense, aeronautics, etc. Because BPL will rely on a wide signal through spread-spectrum frequency use, it cannot simply be notched out or attenuated with RF (radio frequency) filters.
There are now many US private and governmental agencies, some military and public service that have rallied against the damaging effects of BPL technologies. In most cases this is not based on fear of the unknown, but actual testing done at and around the BPL test sites across the country.
Further substantiating these concerns are the trials done in other countries prior to BPL even taking much interest here in the US. As mentioned in the article, in other countries such as cutting-edge technology loving Japan, BPL was discarded due to the detrimental effects to various radio services. Other European countries have scrapped BPL after their own research showed indelible damage to many (some critical) radio frequency based services.
Presently, there are many complaints against electric companies for lossy power lines, bad transformers, insulators, etc...causing RF interference through arcing and RF radiation. It has often been an uphill battle for complaints to be resolved. Yet, on these (some leaky and antiquated) systems, the power companies want to inject powerful large radio-spectrum BPL signals.
Personally, I have no beef against the power authorities, however the proposed systems are worrisome. It would be great to offer broadband to those who cannot easily get it, but in this case the messenger (form of delivery) may need to be shot. There are less invasive means that should be considered.