This FAQ attempts to answer many of the questions surrounding Broadband Over Powerline. Perhaps you’ve seen the controversy in Internet forums, or are investigating the technology. I’ve attempted to target all audiences and keep technical items as easy to understand as possible. I welcome suggestions, comments, questions, or corrections at the email address above.
Q: What is Broadband over Powerline or BPL?
A: BPL is a system that is being tested to provide broadband Internet service via powerlines. Radio energy is coupled onto power lines and is distributed into homes. A device in the home plugs into a normal wall outlet and typically provides an Ethernet connection to a computer or home network.
BPL is also known in some countries as PLT. It can also be referred to as Broadband Powerline Carrier, or just PLC, although the acronym PLC is more applicable to an older technology that is used for telemetry and control in power systems and is not the same thing.
At the time of this writing, BPL is mainly in testing in the United States and a few foreign countries. A few carriers are actually selling the service to customers. BPL is intended as another residential broadband technology similar to DSL and Cable.
Q: Why are Amateur Radio operators, also known as Hams, in an uproar over Broadband Over Powerline or BPL?
A: BPL is a system that is being tested to provide broadband Internet service via powerlines. The system uses frequencies that will radiate into the air and cause interference to licensed services including Amateur Radio. The frequencies BPL uses in general is 1 to 80 Mhz (megahertz). This particular band of frequencies are known as HF (which is actually 1 – 30 Mhz). This part of the radio spectrum has very special properties not found elsewhere. With this band, one can communicate around the world with very minute power levels. This is due to the fact that radio waves in this band can bounce off the ionosphere multiple times to get to the destination. Other portions of the radio spectrum are essentially line-of-sight. This means that the signals cannot bend or bounce off the ionosphere, but they can only propagate like light – in a straight line.
Here is a good visual representation of how much spectrum BPL has the potential to pollute. (BPL is the black “spray paint”)
Q: What is technically wrong with BPL?
A: The medium of BPL (the powerline cable), unlike any other broadband medium (copper twisted pair, fiber, coaxial cable), is inherently unsuited for carrying the frequencies BPL uses. In fact it naturally abhors them, much like nature abhors a vacuum. Power lines, copper twisted pair, and coaxial cable all act like natural low pass filters, meaning higher frequencies are attenuated more than lower frequencies when attempting to transmit them through the medium. The exact slope of the graph of attenuation depends on the specific construction of the material, but in general, twisted pair is suitable up to 100 Mhz and coaxial cable can go up to about 3 Ghz. Again, these are very general figures and determining the suitability for any application depends on other factors. Power lines would be suitable for up to perhaps 20 Khz, maybe 350 kHz at a stretch, with caveats. The exact figure is unimportant for this discussion, but note that this is kilohertz, not megahertz or gigahertz. These are essentially audio frequencies, and equate to a data rate in the neighborhood of ISDN.
The other property of the medium chosen for BPL is its radiating capability. Again, unlike all other broadband mediums, power lines are excellent radiators of the frequencies BPL uses. Copper twisted pair, coaxial cable, and fiber are all inherently non-radiating mediums. It should be noted that twisted pair and coaxial cable do actually radiate to some extent, but in proportion to the amplitude of the signal they are carrying, it is minuscule. (This doesn’t apply to poorly designed or maintained cable or pairs, or intentionally radiating cable like Radiax used for indoor applications). It’s ironic that an antenna in use by some Amateurs called a rhombic actually is very close in construction and visual appearance to typical power lines. Amateurs have often joked through the years that they would have excellent signals if they could only use the power lines in front of their homes for antennas.
No electrical engineer in his right mind would unleash a technology that puts 80 MHz of RF noise and modulated carriers on an unshielded, lossy, radiating medium. Basic first-year college courses teach one this. This is very, very basic. The electrically dirty and unpredictable nature of power lines will also produce harmonics and intermodulation that will cause unexpected forms of interference.
Q: Does BPL work?
A: From a consumer point of view and what has been heard from test areas, yes. Neither I nor the majority of the Amateur community disputes this. The scalability of each of the systems remains to be seen, though, as there are few if any heavily loaded systems. However, one would expect the behavior of a BPL network to resemble that of a shared medium like cable or wireless. Systems will have to be segmented further as traffic grows and the available bandwidth in a segment decreases.
There are significant concerns about immunity to interference which I discuss further later in this document. The effects of such interference are unknown at this point and could make BPL service in areas unreliable or unfeasible.
Q: Why can’t BPL coexist with wireless technologies?
A: To allow a wired-based network to make large portions of frequencies unusable in the RF world is tantamount to allowing human rights atrocities to occur. Cable companies use frequencies in VHF and UHF bands that were they to leak out into the outside world, would wreak havoc with aviation and public safety frequencies. They are subject to strict radiation limits, and there’s no reason why any other wired network like BPL shouldn’t be subject to strict limits – it’s a wired medium, it shouldn’t affect wireless media in any way.
Q: Is BPL new?
A: BPL has been tested and deployed on a limited basis in other countries and was essentially rejected due to interference issues. BPL vendors may claim “new technology” and advances have now made it possible, but the fact is they can’t change the laws of physics. High speed data must occupy a certain amount of “bandwidth” and power lines which were designed to operate at 60Hz will radiate RF that is applied to them. Only changing power line construction (i.e. coaxial cable) would eliminate this radiation. BPL proponents reject this as being too costly, but that would be the cost to make this a real viable technology.
Q: Hasn’t Power Line Carrier or PLC been in operation for years without problems?
A: The “original” PLC is a very low frequency, narrow bandwidth signal used for control equipment in the power grid. It is in the neighborhood of 100 to 180 kHz (that’s kilohertz, not megahertz). It is not intended for high speed data transfer, but rather simple commands, like “turn relay on”, “turn relay off”. It is also used to send “messages” up the line when a major failure occurs so that other network elements don’t trip off when senses a fault. This keeps the power grid from falling down like a bunch of dominoes (like what happen recently with the blackout in the Northeast :-).
Usually people refer to the 1-80 Mhz “PLC” as BPL, although some use the acronyms interchangeably and in my opinion, wrongly. Comparing “original” PLC and BPL is like comparing apples to oranges. PLC is brief, primitive commands and is very narrow banded. BPL is wide band noise that’s all over the place.
Recently the Amateur Radio community petitioned the FCC for a low frequency band in the same area as the original low frequency telemetry PLC. It was rejected by the FCC because utility companies complained that Amateurs would interfere with this telemetry PLC. This is very interesting for several reasons. First off, the utilities are saying that BPL won’t interfere with Amateurs and Amateurs won’t interfere with BPL. But PLC is arguably more robust than BPL because it’s narrow band. So which way is it ? The second reason this was so interesting (or disturbing) is that telemetry PLC is operating under Part 15 and is afforded no protection from interference from licensed services. For the first time the FCC disallowed licensed operation and essentially protected a Part 15 operation. This sets a dangerous precedent as any unlicensed “spectrum squatter” can later claim rights to a chunk of frequencies. The third and even worse observation is that the utilities have admitted that the telemetry system of the national power grid is vulnerable to attack, and they’ve based a critical part of the infrastructure on something that cannot be legally protected from interference. Any nutcase with a little knowledge could conceivably control network elements within a power grid with enough time and money.
PLC has been in operation for a long time, but as I mentioned, it’s very different from BPL. It seems many BPL proponents are confusing the situation by riding on PLC’s history and merits. Their recent defense of “original” PLC with the FCC also illustrates their lack of understanding of Part 15.
Q: Won’t adaptive technology in BPL protect others from interference?
A: Adaptive technology has been proposed by the FCC in the Notice of Proposed Rulemaking as a way to mitigate interference. While sounding high tech, this technology is actually administrative functions that are present in most BPL equipment today. This includes:
- Power control, dynamic or remote
- Frequency notching
- Harmful interference shut-down feature
First off, these techniques do not provide any protection for mobile or portable stations. Dynamic power control is an obvious no-brainer and should be a requirement as this would keep power levels on the lines as low as possible. Frequency notching, while a possible solution for local interference complaints, doesn’t address long range interference that would be created by ionospheric propagation or the cumulative effect on the noise floor in the HF bands. The harmful interference shut-down feature is rather ambiguous in the NPRM, but it seems to be a manual remote control on/off switch. Most network equipment today can be turned off remotely, so this feature isn’t a real stretch, but it does nothing proactively to lessen interference.
Q: If this just affects Ham Radio, why should anyone care?
A: BPL will also affect other licensed services such as government agencies , military, aviation, maritime, public safety, and shortwave broadcasts. Ham radio occupies less than 10 percent of the affected radio spectrum.
Q: Are Hams qualified to talk about BPL issues ?
A: Hams are licensed by the FCC in the United States and various governing bodies in most every country in the world. Most countries have several classes of licenses. In the United States and most countries, one must pass written tests on electronic theory, communications protocol, and regulatory material. While becoming a licensed Ham isn’t equivalent to an Electrical Engineering degree, many hams have formal educations in electrical engineering.
The experience and knowledge of Hams can vary greatly, and like any hobby or profession, there are hams who spout off without knowing what they are talking about. Occasionally you will find an ex-ham dismissing Ham Radio as being dead, or an inexperienced Ham who only uses VHF bands who could care less about the HF bands that are threatened by BPL. Most active hams though are rather knowledgeable.
Q: Why are Hams the only people talking about the negative affects of BPL? Why aren’t other services complaining?
A: Ham radio occupies a minority of BPL spectrum, with government, shortwave, public safety, and ship communications occupying the majority. Ham radio operators are the most vocal because government agency employees quite simply don’t post in Internet forums.
Q: What other services use the HF radio spectrum?
A: A good web page with a sampling of non-Amateur frequencies is here . This is just a sampling of 1000 frequencies of interest and not a complete list of allocations. A chart of allocations from a “30,000 foot” view is here .
Q: Can’t Hams and others using the spectrum simply be relocated?
A: Users of the affected spectrum cannot be relocated, or at least not economically or in a timely manner. It would be cheaper for the government to subsidize cable and DSL deployment. Plus, all of the services that use HF bands require the characteristics that only HF bands exhibit. There would also be huge international treaty implications with any relocation. Changes in international communications treaties are measured in decades, not months or even years. Relocating government and military services alone would take years as the FCC would have to structure a migration plan. Chances are it would be ten years before this could be completed and it’s likely that power companies will have run fiber to the home or DSL and cable will finally be ubiquitous. Perhaps the largest issue to tackle, though, is where to move these services in what is an already overcrowded spectrum.
If it was determined that relocation was the way to go, this would be very irresponsible as HF radio bands are a unique natural resource. No other radio spectrum can provide worldwide communications without any supporting infrastructure (i.e. satellites).
Q: Won’t Frequency Notching protect licensed services?
A: Frequency Notching is a new feature that is reported on some of the second generation BPL systems. (I’ve heard MainNet uses this). The idea is that if a BPL signal is interfering, the system can be configured to not use this frequency or a band of frequencies. This apparently can be done on a subscriber, network, or system wide basis. While this is a nice feature, it still doesn’t make BPL acceptable for four reasons. The first of which is that the possibility of intermodulation still exists. (Intermodulation is described in detail below).
The second reason is that BPL signals can propagate for very long distances due to the characteristics of the frequencies they are using. Interference from a BPL could be experienced a thousand miles away. Tracking this interference down so that the BPL operator could be informed of a Part 15 violation in order to get them to notch the frequency would be logistically difficult. Considering BPL acts like a large distributed antenna and not a classic point-source of interference, it would be hard to direction find the signal to track it down.
The third issue is what’s called the noise floor. The noise floor in simple terms is what you hear in between radio stations on an FM or AM radio. It’s the snowy screen you see on your TV when there’s no station on the channel. The noise floor is essentially noise and radio spectrum energy left over from the Big Bang. This noise is fairly constant, but man-made noise sources such as existing 60 Hz power lines, noisy transmitters and other things contribute to raising the noise floor. BPL systems will contribute to the noise floor and raise it higher. This will make it more difficult to receive weak signals. Taken to the extreme, the raised noise floor could make HF communications impossible.
The fourth reason that notching won’t work is that there just isn’t any significant open space in the HF spectrum. Anywhere you look, there’s a service using the frequency. My guess is BPL providers are banking on the fact that there’s not a local user of particular chunks of HF frequencies, so they will configure their systems to operate in these areas. If we were talking about microwave frequencies that are strictly line-of-sight propagation bands this would be a great solution, but that’s simply not the case with HF. HF has worldwide propagation characteristics, so it’s likely users hundreds or thousands of miles away could experience interference. As mentioned elsewhere here, tracking such wide band no identification interference is nearly impossible.
Q: What is intermodulation?
A: Intermodulation is the mixing of radio signals which produces new radio signals. Think of it as radio waves having children. But just how do radio waves have children ?
This mixing is caused by what are called non-linearities. One non-linear electronic component that you find in most any electronic device is a diode. When multiple radio signals are run through the diode, they mix together. Let’s say we have a 4 Mhz signal and a 6 Mhz signal going into the diode. We would then get:
4 + 6 = 10 Mhz
6 – 4 = 2 Mhz
4 and 6 Mhz had two “children”, 2 and 10 Mhz !
Now, non-linearities are usually good. This phenomenon is used in just about every radio device to either create a signal to be transmitted, or receive a signal that you hear or see. But, non-linearities can occur where you don’t want them and then in causes problems. One such place is in power lines. Bad, corroded connections or dissimilar metals touching can create natural diodes that act like mixers and produce this intermodulation.
So, let’s take a BPL signal and for the sake of discussion, say it’s a grossly simplified consisting of radio signals at 1, 5, 8, 9, and 12 Mhz. Some of the intermodulation products that could be created would be:
1 + 5 = 6 Mhz
8 + 9 = 17 Mhz
9 + 12 = 21 Mhz
12 – 9 = 3 Mhz
But you could also have what is known as third order products:
1 + 9 + 12 = 22 Mhz
8 + 9 + 12 = 29 Mhz
8 – 5 + 12 = 15 Mhz
2 * 12 = 24 Mhz
(9 – 5) * 12 = 48 Mhz
You can do the math and figure out each permutation, but you get the idea. If we took a real BPL signal that has signals from 1 – 80 Mhz the number of products and where they would fall are mind-boggling. The resulting intermodulation products in a system could extend well above the band BPL proponents want, falling into FM broadcast, VHF TV, Aeronautical, and more public safety bands. This is just another reason why BPL is so problematic.
It’s arguable that such non-linearities in power lines are exhibited as arcing connections, something that most power companies are actively searching for these days as the RFI (radio frequency interference) effects are well understood. These maintenance issues will be addressed quickly by well run utilities. However, non-linear loads are common in homes, light dimmers being the first devices that come to mind. Theoretically, these devices could create intermodulation that would in turn be radiated by the house wiring and outside power cabling.
Q: Isn’t ham radio on the decline?
A: Ham bands are not deserted and ham radio is not dying. Ham radio has more licensees than ever. Ham opponents post comments that every time they’ve listened to ham radio, it’s been dead. You never hear any details. Was it HF, VHF, UHF? Were they listening on a band that is subject to the effects of propagation which change based on time-of-day and solar conditions, and were just listening to a band that was dead due to radio conditions? They don’t know. But in this online world, anecdotal evidence carries as much weigh as a ten year study. It should be noted that on many weekends, it can be difficult to find an open, unused frequency on several HF bands. Statistics on the number of ham radio operators in the world is here .
Q: Isn’t ham radio obsolete?
A: Depends on what you call “obsolete”. Hams use numerous modes including CW (Morse Code), Voice (AM, FM and Single Sideband), Video (analog slow scan and fast scan), and data (RTTY, PSK, MFSK, Spread Spectrum). Morse code has been around since the beginning of radio and still thrives as a nostalgic part of the hobby today. Other Hams experiment with cutting-edge modulation techniques, while others prefer older modes. Many Amateurs build their own equipment from scratch.
Electronics engineering basics such as antenna design, modulation techniques, amplifier design, filter design, and transmission line theory never really change, and in Amateur Radio you can learn about these and actually see them in action, and not just read about it.
While Amateur Radio in general isn’t “cutting edge” like it was in previous years, it provides an educational foundation for engineers who will be designing cutting edge technology in the future in the professional world, so to dismiss it as “obsolete” is misguided and narrow-minded.
Ham radio also provides emergency communications services in times of need.
Amateur Radio has continued to thrive through the advent of long distance telephone, satellite, pagers, cell phones and now the Internet, and it will always have a place whether for hobbyist, public service, educational, or international goodwill purposes.
Q: In a disaster when the power goes out, BPL goes out, but so does Ham Radio as well. So what use is Ham Radio in a disaster?
A: Amateur Radio operators pride themselves in emergency preparedness and many are equipped with significant emergency power capabilities and portable low power equipment. There’s an annual event called Field Day in which this emergency preparedness is exercised and improved.
Q: But cellular provides disaster communications, so why is ham radio needed?
A: Cellular networks rely on telco facilities to deliver calls to cell sites. Many carriers do use Part 101 point-to-point microwave instead of telco facilities, but this has largely given way to telco facilities especially in core metropolitan areas where cell densities make microwave prohibitive. So cellular networks are often subject to the same negative impact as wired telco facilities. Additionally, during a disaster, if a portion of the cellular system remains in operation, many times it is so overloaded that it is nearly useless. While ham radio can’t carry an onslaught of phone calls, it is useful in delivering messages across the country and world. Some of these messages may be a simple “I’m OK” type message from one family member to another and seem insignificant. But, if you’ve ever been in the situation on the other end waiting, you know such an insignificant communication is priceless.
Q: If the power goes out in an area, BPL interference will go out as well, so Hams could then provide emergency services, so what is the problem?
A: Amateurs need to maintain equipment and practice needed skills before a disaster occurs. If the equipment is unusable during regular times, what is the motivation even to buy equipment? Another thing to consider is that emergency stations need to be able to communicate out to areas that do have power.
Another issue to contend with is the propagation characteristics of the HF band which BPL is using. Interference could travel thousands of miles. I doubt anyone will want to track down interference a thousand miles away when a hurricane has just flattened their state.
Q: Why can’t a national “off switch” for BPL be implemented so that during times of emergency BPL could be deactivated allowing interference free radio operation?
A: This makes an assumption that only emergency HF communications are needed and normal day-to-day communications are not. This is not the case. Looking at this sampling of non-Amateur HF frequencies, there’s a massive amount of day-to-day communications for aeronautical, military, and other government agencies.
Assuming for a moment that we could live with only emergency communications and were going to implement a mechanism to turn off all BPL on command, the logistics of such of system would be staggering. Who would trigger such a switch? If it was a linked system, how would it be secured? What if companies wanted to legally challenge activations as any activations of the system would impact their bottom line?
The FCC declares communications emergencies several times a year in which Amateurs must avoid the use of several frequencies so that emergency traffic can be passed. Assuming a national off switch would be synchronized with this, BPL users could expect to have outages lasting several days or weeks, multiple times of the year. This quality of service would make the worse BPL or cable look wonderful.
Q: Are the American Radio Relay League or ARRL and/or Hams shills for the telcos, cable, and other commercial interests?
A: Hams are individuals like you and me. The ARRL is non-profit and represents ham radio in the US. The Baby Bells are well funded but would have a hard time buying off 700,000 Hams. They are interested in stopping BPL due to business issues and Hams could care less about this.
Q: But BPL complies with FCC Part 15, doesn’t it?
A: BPL compliance with Part 15 is meaningless. Part 15 basically states that the unlicensed device must generate no interference and accept all interference from licensed services with no recourse. Power companies in general have a particularly poor record in responding to interference from their existing 60 Hz power transmissions. The FCC is enthusiastically seeking comments on relaxing Part 15 to encourage BPL. BPL vendors know that they can deploy BPL right now under Part 15, but they know widespread deployments will open a Pandora’s box of interference complaints. Even if they are Part 15 compliant, they will have to cease operation if the network is interfering.
BPL vendors have proudly released press releases stating Part 15 compliance, as if this proves evidence of no interference. This is simply PR fluff as it merely means measured signal emissions are within mandated limits. In the HF bands, the emissions limit is 30 uV/m (microvolts per meter) at a distance of 30 meters. It’s not important to know exactly what this means, but know that this signal level will cause interference in any well designed HF radio equipment. Once interference is detected, the second clause in Part 15 goes into effect, and the system must cease operation regardless of compliance with the mandated emission limit.
Part 15 compliance or certification should not by any means be considered a milestone for product success or investment.
Q: BPL is being tested in several areas. Shouldn’t the negative affects be seen in these test areas?
A: BPL tests in the United States haven’t been widespread enough to understand fully the implications. Experiments have been mostly on a street or city block level. Judging by the recent FCC Notice Of Inquiry filings from BPL proponents, little if any measurements have been taken.
Q: If the interference problem is not solved and this is deployed, what will happen?
A: If BPL is deployed in its current state it will be a mess for both sides. The FCC will be inundated with interference complaints which will stress its limited resources. Customers of BPL will experience unreliable service due to interference in many areas. Utilities will become frustrated with trying to troubleshoot the service problems and will undoubtedly lack the equipment or expertise to identify interference ingress into their system. Ultimately investors in the technology will lose out as well. It’s a losing proposition all around.
Q: Won’t BPL create more “effective bandwidth” out of what limited resources we have?
A: BPL is a wired network impacting wireless radio spectrum. Wired networks are intended to do just the opposite – not impact wireless frequencies. One wouldn’t run a wire to a car or SUV to provide mobile phone service to that vehicle. And deploying BPL actually exacerbates the ongoing radio spectrum congestion problem, and does not create any additional “overall bandwidth” in the world. And as I mentioned before, relocation of existing services in the HF band is a very, very monumental task taking years of work and substantial costs that have not yet been identified.
Q: Don’t these new modulation techniques like OFDM reduce or eliminate interference ?
A: While techniques like OFDM may change the distribution of radio energy across the radio band in use, it will not reduce interference. Consider this analogy. In a restaurant at a table next to you, if someone speaks loudly in English, and then changes to French or German, the voice still speaks at a certain volume and can interfere with your ongoing conversation at your table. Ignoring that the human brain can naturally block out foreign languages, different languages may change the tonal qualities, but the overall amplitude of the sound waves is still the same.
BPL equipment designers are limited to an emission level of 30 uV/m at a distance of 30 meters. They are naturally going to run the highest power level possible on the line, staying withing this emission limit. The higher the signal level, the less repeaters are needed and it makes the system more economically viable. So, running different modulation schemes will result in the same 30uV/m emissions level.
Q: How else can power companies get into broadband? Isn’t this their only choice?
A: Power companies should be building for broadband dominance in the coming decades and beyond with viable technology like fiber, not for the next year or two with doomed-for-obsolescence technology. If the utility companies are in a frenzy to get their proverbial “foot in the door” before telcos and cable companies snatch up their potential customers, fiber delivery to the last mile and 802.11 wireless on poles for the last 100 feet makes a ton of sense. This is not a new idea and some carriers are doing it now.
Q: Doesn’t the need for broadband outweigh the needs and value of ham radio and other services using the affected spectrum?
A: Destroying a large portion of wireless spectrum is not justifiable because it benefits more people. There are many examples of this in society where reallocation of a resource would benefit more people, but it would be detrimental long term to the people and the resource itself. Right now, amateur frequency allocations belong to the people internationally. You can enjoy them by simply passing a test and getting licensed. Once they are given to a business interest, they cease to be yours and you can only use them as a customer of that business. BPL impacts other groups including government, military, shortwave, aviation, maritime communications, and CBers, so this would have national security and international implications as well. BPL has been linked in some rhetoric with increasing “homeland security”. BPL in fact takes spectrum away from government agencies directly tasked with protecting the country. So in summary, allowing BPL will ultimately benefit a few utility companies, not the people.
Q: Why would anyone propose a broadband system that isn’t viable?
A: Potential revenue, an FCC that is very pro-big business lobbyist friendly and technically lacking, a high demand for broadband from a starving public, and the classic promises of broadband (also known as hype) are driving BPL.
Q: Why have BPL proponents (like the APPA) stated that the responsibility of proving interference is that of its opponents?
A: BPL proponents have claimed interference is not an issue, but haven’t put in any hardcore measurements into their NOI filings (that I’m aware of at this writing). Either the measurements haven’t been taken by them, or they have them and are withholding them. In selling a technology or anything to investors, regulatory agencies, or the general public, one normally is more than happy to provide supporting data to defend a proposed product, so this is puzzling to say the least. Unfortunately it will be up to opponents to spend considerable time and expense taking measurements that the BPL industry should have done in the first place and submit them to the FCC.
Q: Won’t BPL give me cheaper broadband?
A: Perhaps, but the costs to deploy BPL are still there. Repeaters and the BPL equivalent of DSL DSLAMs will need to be deployed. BPL promises to deliver broadband in areas that cable and DSL don’t so there will be no competition to drive down prices. The costs to deliver to these less populated areas will be higher, so the motivation for low prices in these area is absent. But it’s likely BPL will be deployed exactly where cable and DSL is now because that’s where the revenue is.
Q: What is 802.11 / WiFi / 2.4 Ghz / 5 Ghz High Speed BPL?
A: This is a recent development which uses frequencies at 2.4 Ghz or 5 Ghz and not HF frequencies. It should not interfere with licensed services such as Amateur Radio in 1-80 Mhz. Amateurs have a secondary allocation at 2.4 Ghz, but have been living fairly harmoniously with unlicensed 802.11 operations there. The propagation of 2.4 and 5 Ghz is much, much different than that of HF. Such frequencies will travel only a couple miles and is strictly a line-of-sight. HF spectrum can travel around the world with only milliwatts of power making any BPL operations in this band dangerous.
I have my doubts whether this high speed BPL will actually work, but as far as interference concerns, I have nearly none. The BPL that occupies 1-80 Mhz is a train wreck technologically and will be a disaster for everyone involved. The FCC and investors should be looking at this high-speed BPL and quite simply trash HF BPL as a bad idea that looked good drawn out on a napkin after five drinks at the company Christmas party. If they can make it work and it’s strictly 2.4 or 5 Ghz, I say have at it.
Q: What is the technological basis of 802.11 / WiFi / 2.4 Ghz / 5 Ghz High Speed BPL?
A: The creators of this system are taking advantage of a technique perfected by Georg Goubau, more commonly known as G-line. A good web page describing G-line is here. Ironically, a Ham, George Hatherell (ex-K6LK or SK ?), wrote about G-Line in a 1974 QST article entitled Putting the G Line to Work.
Q: Do you think WiFi / 5 Ghz BPL will work?
A: G-line, the discovery that this BPL is based upon has one troublesome requirement – the cable must be coated with a dielectric, like a low-loss plastic. Most power lines are bare conductive metal and coating or replacing all of these is a rather difficult and expensive undertaking. Also, the cable used in G-line cannot have sharp bends, otherwise the microwave energy just floats off into space.
If this is used like a radiating line with the “drops” to houses being wireless rather than conducted RF on the line, this may just work. Considering the effective radiated power limit in the upper 5Ghz band is four watts, a 5 Ghz BPL system could use significantly more power than a low speed HF system, reducing the need for repeaters.
Q: Won’t 802.11 / WiFi / 2.4 Ghz / 5 Ghz High Speed BPL interfere with UNII band Wireless ISPs , 802.11 indoor wireless LANs, or 2.4 Ghz or 5 Ghz cordless phones?
A: This could have the potential to interfere with existing 5 Ghz UNII band operations such as wireless ISPs (WISPs). However, all of these devices are on equal regulatory footing as they operate under Part 15 rules. Something to consider, though, is the nature of 2.4 and 5 Ghz signals. They do not propagate like HF signals that the low speed BPL uses. This is microwave frequencies, so it propagates much more like light – in straight waves, or line-of-sight. So any radiated emissions could be expected to be stopped or severely attenuated by vegetation and buildings in short order. I’d suspect that indoor wireless LANs could easily overcome any emissions from such a system, and wireless ISPs using directional antennas would not have problems.
Specific to 5Ghz, there are three bands which we’ll call lower, middle, and upper. The lower band is strictly for indoor use due to some legacy government applications in this band. 5 Ghz cordless phones and 802.11b wireless LANs operate in this band. Any outdoor BPL would operate in the middle and upper bands, so interference for 5 Ghz consumer devices should not be an issue.
Q: Why have so many people attacked Ham Radio in forums ? Why does the information above conflict with what people have told me in forums?
A: There’s a vocal minority of uninformed people who want broadband Internet in the worst sort of way and are willing to dismiss anything they are unfamiliar with or unaware of, or if it simply doesn’t affect them. The Internet has created this world of anonymity where ignorance and anecdotal evidence with no supporting facts is taken as gospel. When forum debaters can’t attack the evidence, they attack Ham Radio. Before you take the word of someone online with an AOL-like screename spelled in hacker language ( 733t H4X0r spe4k), listen to the people who are licensed and understand what they’re talking about.
Q: Many major discoveries and inventions throughout history first met with failure. Determined scientists and inventors who ambitiously pursued their goals ultimately triumphed and were able to succeed and produce products that benefited the public. Perhaps BPL is in the same category ?
A: The invention of BPL isn’t quite on the level of the discovery of plutonium or the invention of the telephone. The radiating characteristics of conductors were discovered a century ago and the concept of carrying radio frequency on power lines (also known as Carrier Current and described below) has been in use for decades.
One could argue that perhaps BPL engineers have discovered some new phenomenon that changes the laws of physics. I’d counter that if they did, there’d be numerous papers in the scientific community describing the phenomenon, and the applications of a such a discovery would have much, much more lucrative applications beyond BPL.
Q: Couldn’t Hams use power lines as antennas?
A: Technically anyone can as long as they operate under Part 15 rules. This concept is called Carrier Current and is used by some unlicensed (legal) AM broadcasters. This is done by injecting very low power radio frequencies into the line. The difference between classic Carrier Current and BPL is that Carrier Current uses one distinct frequency, typically a standard AM channel. BPL is wide band in nature and uses several megahertz. Note that the entire reason someone would use Carrier Current is that the power lines radiate the signal, acting like a distributed antenna – something many BPL proponents claim just doesn’t happen. If Hams used power lines as antennas with typical Amateur power levels, the results would be disastrous with massive interference to many residential devices.
Q: Won’t BPL radio energy on power lines be detrimental to people ?
A: No, the low power levels that BPL uses will not have detrimental biological effects.
Q: People who already have broadband Internet oppose BPL because they don’t care about the people who don’t have any broadband choices. (Statement, not a question.)
A: Hams are people like you. Hams want broadband just as much as anyone else and the same percentage of Hams as the general population are dealing with the same lack of broadband Internet. You don’t see Hams standing up and blocking cable or DSL deployment, so to say that this is entirely a movement of people who don’t care about “broadband challenged” citizens is just plain wrong and perhaps one of the stupidest arguments I’ve heard to date. The movement against BPL is strictly technology based.
Q: Hasn’t FCC Commissioner Powell stated/mandated than any broadband pipe to the home is welcome?
A: Powell is a politician and broadband is a hot button topic for many Americans. He will earn considerable points if he could deliver broadband. Whether you’re a Democrat or Republican, liberal, moderate, or conservative, you have to recognize the political realities of the current FCC administration. They are Republicans. Republicans don’t support regulation, and won’t take the necessary steps to subsidize/fund/mandate/encourage DSL, Cable, and wireless deployment in the boonies. On the contrary, Powell has worked to preserve these monopolies. Additionally, the Bush Administration is very pro energy business and pro big business, so electric utilities and their lobbyist organizations are calling the shots with the FCC.
Q: Won’t the FCC protect licensed services? The FCC wouldn’t let bad things happen, would they?
A: It’s the FCC’s mission to protect licensed services and promote good use of the spectrum. I don’t feel the FCC would intentional wreck spectrum, but in their fervor to have a broadband victory, they seem to have forgotten their directive of protecting licensed services.
Q: Won’t BPL be different than Cable and DSL and deliver broadband to those who don’t have it, especially in rural areas?
A: If you don’t have broadband now, there’s probably one good reason – lack of sufficient revenue in your area. People are mistaken in thinking that BPL providers are going to go out of their way to deliver BPL to country folk, as if this is some kind of humanitarian effort to get the country on the ‘net. It’s not. Companies are in business to make a profit, plain and simple. Being a good corporate citizen in a community makes great press releases, but such efforts stop when the bottom line is affected.
Let’s talk about the differences and similarities between Cable, DSL, and BPL for a moment. Cable requires a unit at the origination of the cable system, also known as a headend. This unit is expensive, but can service hundreds to thousands of customers. The cable system is already built with repeaters for the video part of the system called amplifiers. So the major investment for cable is at the headend, and service can be delivered basically anywhere cable already is deployed. The upstream Internet network must be brought to a single point, the cable headend.
DSL is based out of telephone central offices using a device or peripheral called a DSLAM. Like a cable modem headend unit, it can provide service to hundreds of customers. DSL service can be provided about 18,000 feet from the DSLAM. This has severely limited DSL deployment. As with cable, the upstream Internet network must be brought to a single point, the central office. Any ILEC or CLEC probably already has significant Internet bandwidth available at any central office serving business customers.
BPL service is provided by a DSLAM/Cable headend type device, but its effective distance is 200 meters or 656 feet. Every 200 meters a repeater must be used to regenerate the signal. BPL service can’t really be distributed from a central point like Cable or DSL, so the upstream Internet network must be backhauled to each BPL feed point via telco facilities such as fiber or copper.
So to deploy BPL an up front investment must be made in BPL headend/feed point equipment and repeaters. There’s going to be significant recurring costs in backhauling the IP traffic from the numerous BPL feedpoints serving an area. Neither DSL or Cable has this recurring cost or need for multiple network origination points. These costs unique to BPL make it even less attractive for deployment in rural areas that Cable or DSL as customer densities and revenue potential is lower. While it may be stated by BPL providers that initial metropolitan buildouts are needed to subsidize rural deployments, why would any for-profit company expand into rural areas when it’s a losing proposition?
Q: Is there a way that BPL could be made to work?
A: This is strictly my opinion, but here’s my thoughts:
1. Limit all BPL deployment to underground cables.
2. Confine BPL to a set, dedicated band of spectrum, perhaps 1 Mhz of spectrum that will have the least impact to all licensed services.
3. Set installation acceptance regulations that specify measurement standards and mandate periodic measurements and record keeping.
4. Set out of band spurious emissions limits to an acceptable level to all licensed services. This would need to be much more stringent than the current 30 uV/m at 30 meters limit in Part 15.
5. Set the in band emissions limits to an acceptable level, although less stringent than the out of band emissions above.
6. Require equipment certification beyond Part 15 for all BPL equipment.
7. Add additional language to Part 15 to apply appropriate emissions limits to broadband devices operating on HF frequencies.
I haven’t fully developed these guidelines, but I’m basically saying that BPL shouldn’t be a Part 15 device because it doesn’t fit the historical Part 15 “mold”. I think a new section in Title 47 needs to be created to accommodate it as its effects could be widespread. Part 15 was meant to allow devices like cordless phones to operate, not for telecommunications companies to create regional networks supplying services to thousands of customers.
Some may argue that Part 15 has done its job over the years, despite the rather loose emission limit, but I’d respond that BPL isn’t your typical Part 15 device. 30 uV/m at 30 meters is great when you’re dealing with a single point source, but not for large distributed antennas run by large corporate interests with questionable response times to interference complaints.
Q: Why don’t the utilities just bury all the power lines to lessen interference?
A: If digging up the entire country for power line burial would be an option, it would make better sense to just run buried fiber everywhere. Fiber has so much, much more bandwidth compared to BPL it would be frivolous to go through such a drastic project just to bury cabling that can ideally carry only 100 kHz of bandwidth.
Q: Shouldn’t Hams be responsible for coming up with an alternate broadband solution?
A: Hams are merely the messengers, or the “canaries in the mine” as I like to say. Hams cannot use their spectrum for commercial purposes, so designing an alternate over-the-air technology using ham frequencies is out of the question. The responsibility of providing a broadband solution over power lines or other mediums is not their responsibility as some have suggested. BPL is a technology dreamed up by commercial interests with profits in mind. Some who have delusions that BPL is a humanitarian effort to deliver the Internet to huddled masses of rural folk starving for bandwidth are overly idealistic and unrealistic. This is a business with one thing in mind – revenue.
Q: Why don’t Hams work to help solve the problems of BPL they claim exist?
A: At the time of this writing, the ARRL is assisting several BPL manufacturers at various levels. Some have been more cooperative or welcoming than others. I suspect some fear ingress interference from higher powered Amateur stations, and are cooperating with their interests in mind.
I personally would have no problem with helping a utility or a BPL vendor take measurements and I’m sure others would volunteer. I doubt anyone in the Amateur community would be interested in improving the BPL product though, as its foundation is considered too weak to make it work. I also wouldn’t want my volunteer time to contribute to the coffers of a corporation.
Q: Why are some Hams so emotional in their opposition to BPL ?
A: There’s several answers to this. To some extent, the BPL issue is much like an environmental issue. BPL would pollute valuable radio spectrum which is really a natural resource when you think about it. Once the FCC relaxes emissions requirements, the horse is out of the barn and there’s no turning back. It angers many Hams that what should remain confined to a wired network is radiating out into the air and polluting this spectrum. Most lay people do not understand RF theory or the impact of BPL. What is common sense to Radio Amateurs and Electrical Engineers isn’t to the general public. I think this really frustrates Hams.
Another cause of this emotional response is the BPL vendors and the journalists reporting on BPL. Most articles on BPL have been very rosy and fail to mention the severe disadvantages and the ongoing debate. It seems many journalists merely take BPL vendor press releases and transform them into articles. They are either too lazy or just incompetent and don’t dig deeper to get the full story. Some BPL vendors have been arrogant in their response to the interference issue, claim it doesn’t exist, but they clearly haven’t taken field measurements. Others have filed NOI comments that are clearly wrong, or have comments that disagree with what their own models say.
The third cause I believe is the response of some in Internet forums to Ham Radio as being outdated and in need of being eliminated. This display of ignorance is incredibly frustrating and often Hams are arguing with anonymous posters. These anonymous posters can pretty much say whatever they want without stating their qualifications or basing their arguments in reality. This is nothing new as the Internet has been enabling clueless people since it went mainstream in the 90s. Hams are technically minded and most despise wrong information and will stubbornly debate anyone to the bitter end.
I think one will find though, that most Ham forum posts and web pages, however emotional, are largely factual. This has been a hot button topic within the community and anyone involved in the issue usually has read up on the subject.
I’ve attempted to remain unemotional in this FAQ. Any emotional responses here aren’t intended and are more likely due to my writing style 🙂
Q: Do you wish to stop BPL?
A: My problem is with the interference generated with BPL, not BPL itself or broadband. If someone came up with truly interference free BPL I’d support it.
Q: What is your take on the recent FCC Notice of Proposed Rulemaking (NPRM FCC 04-29) ?
A: The FCC ignored just about every argument and piece of evidence against BPL, and gave BPL proponents most everything they wanted, short of lessening Part 15 emissions requirements. The proposed interference mitigation techniques do little to proactively protect licensed services.
Q: What are your qualifications?
A: I currently work in IT at a regional ISP and CLEC. I have experience in RF engineering in HF, VHF, UHF and microwave frequencies. I’ve deployed unlicensed Part 15 wireless Internet services and I’m an avid Amateur Radio operator who builds equipment and enjoys QRP (low power) operation and CW (morse code). I am President of a local Amateur Radio organization and a member of the American Radio Relay League.
Q: Have you experienced BPL interference?
A: Luckily BPL has not been deployed near my home and probably never will be due to my rural location. (Ironically I have a cable modem). I’ve received an Ambient BPL system while operating mobile and plan to take further measurements and publish them as soon as I get the time.