BPL update - Tasmanian DS2 G2 trial

Many Australian hams will have heard the spate of press announcements early last month of intended BPL trials in several locations in South Australia, Melbourne and rural Victoria, and Canberra. These trials are in addition to the long running trials in Hobart, Burnie, and Queanbeyan.

Justin, VK7TW, re-visited the Hobart trial sites again in March, making measurements of the background noise level adjacent to the trial sites, and the level of emissions at several locations within the trial area. He also performed a series of measurements at one site where “notching” technology is employed to reduce emissions across the 20m band.

His latest findings are in two reports.

Justin's reports note that BPL emissions raise the ambient noise power density in the trial precincts by between 15dB (or 32 times) and 41dB (or 12,600 times) in the absence of apparent notching. That means an ambient noise level on 20m in excess of S9 at some of the locations.

Notching is a filtering technique used to reduce emissions in specific frequency bands. The reduction is limited in depth at the source, and expert opinion is that there will be some dilution of notches due to inter-modulation inherent in devices attached to the power lines.

Justin's measurements of the notch performance at Mount Nelson show a reduction in emissions within the 20m band compared to emissions on the adjacent frequencies, by up to 20dB (or 100 times), but the notch does not reliably deliver better than 10dB (or 10 times) reduction in emissions.
BPL emissions raise the ambient noise power density on the 20m band where the notch was deployed by between 5dB (or 3 times) and 15dB (or 32 times).

Justin's reports are available online at the REAST website, reast.asn.au , follow the BPLWATCH link at the top of the home page (http://reast.asn.au/vk7bplwatch.php#emissionmeasurements).

Justin has demonstrated the ingenuity of amateurs in using available resources to make meaningful measurements, and his report of the analysis and conclusions clearly demonstrates BPL to be spectrum polluting and a serious interference risk to radiocommunications services. Well done Justin, a lead for others to follow.

With plans for wider BPL deployments, more amateurs will gain the opportunity to witness its spectrum pollution first hand.

Wait and see... BPL may be coming to a power point near you sooner than you think!

Sound file of story (2:30, 0.6MB): TasBplUpdate.mp3

Owen Duffy, VK1OD

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