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rf_engineer
join:2003-08-04
USA
| reply to Fox McCloud
Re: BPL interference and the ARRL
said by Fox McCloud  :What some fail to realize is that the ARRL operates BPL directly at their HQ in Connecticut, and they have no reported any problems (this is the BPL that operates on low voltage). Thus, it doesn't create any interference. Yes and no. The particular system at ARRL HQ doesn't create interference to Amateur Radio spectrum. Amateur Radio spectrum is only about 9% of the HF (1-30 Mhz) spectrum, the rest is military, aeronautical, maritime, government, CB, international broadcasting and others. Plus, the 30 to 80 Mhz range some systems use contains business and public safety two-way frequencies. While notching can address these other users on a case-by-case basis, it still places the burden on wireless licensees of identifying the interference, proving it's the BPL system causing it, and requesting resolution from the BPL carrier which historically has been a long and drawn out process. It's a concept that basically puts unlicensed services with nearly the same privileges as licensed spectrum users, something the FCC has never quite realized or acknowledged or explored the implications.
I will agree though that the BPL system approach with wireless as the backbone and BPL on the LV drops to the home makes the most sense and has the best chance of succeeding. | |
W1RFI
join:2003-05-12
Burlington, CT
| Interference update:
The system that is installed at ARRL HQ is made by Motorola. It uses their Canopy wireless as a backbone, and then HomePlug modems on the LV (240 v) wiring to get into premises. HomePlug has included notches in the Amateur bands in its specificiations. The Motorola modems have additional filters to improve the notches. When tested at ARRL HQ, the signal was loud and clear outside the Amateur bands (ie, shortwave broadcast), but inaudible in Amateur spectrum. When the W1AW radio bulletin transmitters fired up with 1000 watts simultaneously on 7 Amateur bands, system was not affected.
One other BPL system that has been pretty thorougly evaluated by ARRL is the Current Technologies system, as deployed in Cincinnati, OH. It operates 32-48 MHz on overhead lines, and uses HomePlug modems to get into premises. Although, IMHO, some interference is possible, to date, there have been no interference reports from Cincinatti. The BPL signals there are loud and clear from 32-48 MHz and as I drove around in Cincinnati, I noted that the noise in the shortwave broadcast bands was pretty strong. Amateurs have reported some interference to shortwave broadcast, but none have filed a formal complaint about same to the utility, to Current, to ARRL or to the FCC.
Other BPL has not fared well. The DS2 generation 1 products were notorious for causing interference, and the notching is not very good. Just yesterday, I was in Briarcliff Manor, NY and noted that the Ambient DS2/G1 system there being operated under an experimental license was again quite loud in some of the Amateur bands in some areas of the installation.
There is some progress with notching. DS2 has, for example, improved the generation 2 notch depth. I have only had an opportunity to look at a couple of DS2/G2 systems, and to get a few preliminary reports from local Amateurs. So far, the improved notching is looking promising, although based on the past records of some of the BPL manufacturers involved, it is necessary that they and ARRL work closely together to answer each others' questions before I would expect ARRL to make public statements such as it has done for Motorola and Current Technologies' products. So far, some manufacturers have talked about talking about this; others have started to work with ARRL and/or local Amateurs.
The premise that interference is a dead issue, however, is far from over. The BPL system in Briarcliff Manor is an older technology, but still generating strong interference to Amateur Radio. That interference may or may not be greater than the level that the FCC permits for interfernce to mobile stations, but the bottom line is that it is there; it has not been measured and, so far, the manufacturer has not done anything effective to address it. To the contrary, they have steadfastly claimed that the interference doesn't exist. (I am thinking that a video showing this over the entire area may be needed to really document how to do it wrong.)
Other manufacturers have gone well beyond the requirements of the rules (indicating, of course, what the rules SHOULD have been, to help manufacturers know what is necessary to have a successful product). HomePlug, for example, has fixed, effective and permanent notches in its industry specification. This works; to date, with millions of HomePlug devices installed, ARRL has not received any reports of harmful interference.
Yet the rest of the BPL industry steadfastedly resists effective rules and blocks any attempt to include this sort of mitigation in the developing IEEE BPL standards. This is, IMHO, a tremendously wasted opportunity, and the evasive denials that have been the first reaction from this industry has, IMHO, been a factor in the slow deployment of BPL.
It is not a surprise to me that the largest major successes so far in BPL -- the Current deployment in Ohio (60,000 homes passed) and the pending 2,000,000 homes passed deployment in Dallas are based on technology that has effectively addressed EMC issues.
The other issue discussed in this post has been ingress -- interfernece TO BPL from licensed transmitters. We have seen very positive results from Motorola's approach. DS2-based systems, both G1 and G2, have shown immunity problems to as little as 5 watts. More recent tests conducted by ARRL showed the following general trend:
o 5 watts of in-band transmitter carrier stopped the system cold
o It took, however, 200 watts of out-of-band transmitter carrier to block the system
o Of note, the system auto recovered after about 30 seconds
o In band, 600 watts of transmitted voice signal, slowed the system down, but it did not stop operating. The slowdown appeared in bursts, with data getting through in between syllables.
All in all, this was pretty encouraging, as it shows that, if careful selection of frequency and notching is done to avoid locally used spectrum, transmitters like mobile low-band VHF and typical mobile Amateur operation will not take the BPL system out of service. Such interference will slow it down, with the probable effect that time-critical uses such as VOIP and streaming video would have issues over BPL near radio transmitters. (Of course, such issues could exist with other broadband technologies, too.)
To my knowledge, this is the first testing that has compared the interference from transmitted carriers (as test signals) and transmitted single-sideband voice and on/off keyed CW.
Ed Hare
ARRL Laboratory Manager
225 Main St
Newington, CT 06111
Tel: 860-594-0318
Email: W1RFI@arrl.org | |
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