Submitted by: 73, Lee, N6AXB
The ARRL Letter - Vol. 25, No. 12 - March 24, 2006
BPL CHIP MAKER SHOWS INTERFERENCE ABATEMENT IMPROVEMENTS TO LEAGUE
A demonstration at ARRL Headquarters of DS2 BPL equipment suggests the chipset developer and manufacturer is working to minimize--if not altogether eliminate--interference from its products on amateur bands, ARRL Laboratory Manager Ed Hare, W1RFI, says. Hare met with two DS2 officials at ARRL to discuss the company's improved approach to Amateur Radio band notching techniques. Based upon his observations during a demonstration of DS2's latest generation G2 technology, Hare says he's cautiously optimistic. A spectrum analyzer check of the modem's output showed the G2 modem could attain a notch depth of up to 40 dB.
"While there's no certainty that all BPL products using this technology could achieve 40 dB of protection within notched spectrum, our tests show the capability to do so is there," Hare commented. "This may not prevent all interference problems, but a 10 to 15 dB improvement over the notching used by many BPL systems in place today would be a significant improvement."
Hare points out that DS2 chipsets are used by BPL equipment makers Ambient, Amperion, Corinex and Mitsubishi, among others. "Our work with DS2 could help manufacturers as they address interference problems in earlier-generation equipment," he said. In its October 2005 Petition for Further Rule Making in the BPL proceeding http://www.arrl.org/tis/info/HTML/plc/filings/BPL-FNPRM.pdf, ARRL cited BPL systems using Main.net and DS2 chipsets as among those that lack fixed, permanent notches in the ham bands and "have caused numerous cases of harmful interference to stations in the Amateur Service."
Hare says he was intrigued by an earlier demonstration showing that DS2 had improved the notching capability of its latest chipset. Preliminary tests showed that although close-in notching wasn't much better than other systems', BPL noise dropped below the ambient noise level deep into the notches. Hare and DS2 agreed to work with ARRL to further investigate the notching improvements.
On March 9 DS2 Vice President of Technology and Strategic Partnerships Chano Gomez and Product Manager Eduardo Lluna, EA5ETP, brought a pair of modems using DS2's latest-generation G2 technology to ARRL Headquarters. Gomez directs DS2's US office in California. Lluna is based in Valencia, Spain. The modems were set up in the ARRL Laboratory's screen room, and checked on a spectrum analyzer in the 20-meter band. Hare said the 40 dB notch depth across the entire band was typical of all bands measured.
The DS2 modems also were tested at Maxim Memorial Station W1AW, where they were plugged into outlets in separate parts of the building and set to transmit data. Hare listened on a number of ham bands and on adjacent spectrum. Inside the ham bands, the signal was inaudible, he said.
"Although this was encouraging as a reasonable quick-look test of DS2 modems on premise," Hare cautioned, "testing on a BPL installation using overhead power lines would present a more realistic situation from which to draw firm conclusions." Gomez offered to look into ways such tests might be arranged.
Gomez said he's happy to be working with ARRL to demonstrate that DS2's chipsets are Amateur Radio-friendly. "We have made a huge effort to ensure that the 40 dB programmable notches in our OFDM chipset provide adequate protection," he said. Lluna said several vendors already have deployed DS2-based equipment in the US, "and this gives them the mechanism to avoid interference problems completely." Feedback from the ARRL "has been invaluable" in achieving that goal, he added.
Afterwards, Hare, Gomez and Lluna discussed BPL and electromagnetic compatibility (EMC) issues and potential solutions to head off most cases of interference. "We had a solid exchange of ideas about the technical aspects of interference problems and how improved notch depth could be combined with other techniques to prevent and correct interference," Hare said. "The DS2 staff has a good grasp of the technical issues involved and believes many of them ultimately can be implemented in deployed systems."
ARRL CEO David Sumner, K1ZZ, concurred with Hare's cautious optimism. "We very much appreciate this dialogue with DS2, and we are looking forward to turning talk into action and solutions," he said.
Elmers Corner:
Hints & Tips
Recently, I listed the US Navy antenna handbook. Not wanting to slight another branch of the services, the USMC antenna handbook is another good reference. It can be downloaded at https://www.doctrine.quantico.usmc.mil/htm/doc8.htm. (Thanks, Brian KB9BVN)
The major US automobile manufacturers each publish a guide to installing radio equipment in their vehicles. These are full of good information about grounding, cable routing, noise management, and so forth.
General Motors - http://service.gm.com/techlineinfo/radio.html
Chrysler - http://www.arrl.org/tis/info/pdf/INSTG01.pdf
Ford - http://www.fordemc.com/docs/download/Mobile_Radio_Guide.pdf
The following Web site will give customized sunrise/sunset for almost every city in the USA http://www.sunrisesunset.com/usa/. Select your state and city, then select Astronomical Twilight to get the actual sunrise/sunset times for each day of the selected month. (It prints best in "landscape" orientation.) The US Naval Observatory site, http://aa.usno.navy.mil/data/docs/RS_OneDay.html, is also quite good. For standalone software, Geoclock is the best, but a simple free program by W4SM is TrakSM which is available at http://www.keplerian.com (Thanks, George K8GG and Matt WV1K)
Matt WV1K also contributes this neat link to a site that lists Big Towers - http://en.wikipedia.org/wiki/List_of_Masts. If your ego is threatened by towers larger than yours, don't go there.
Somewhat simpler and easier to deal with than a ground plane antenna on Top Band, John W2GD recommends the vertical dipole he uses at P40W. The big advantage is that no ground system is required, although ground screens help cut losses. An 80/160 version of the antenna is described at http://www.yccc.org/Articles/double_l.htm Tuning the antenna is easy - adjusting the length of the lower leg. Try to pull the top leg out as horizontally as possible, but it will still work even with a significant angle toward the ground.
Do you have audio questions? Try Shure's excellent educational page on microphones and audio electronics http://www.shure.com/support/technotes/default.htm Fans of older microphones and such will enjoy the Web site http://www.coutant.org/contents.html you want to roll your own filter, check out the free design software at http://www.aade.com/filter32/download.htm. It not only helps you design a filter with all the standard types, but it also shows you the response, return loss, etc. in graphic form. (Thanks, Larry N8LP)
The MFJ-1026 Noise Canceller has been around for a while, yet getting it to cancel noise can be tricky. Tod K0TO contributes his procedure that may help others find a null in the haystack http://www.k0to.us/HAM/Noise/adjusting_MFJ-1026.htm.
Hubbell Power Systems provides a useful "Encyclopedia of Anchoring" at
http://www.hubbellpowersystems.com/powertest/chance/earth_anchors.html given the critical nature of guys to one's tower remaining vertical, this is an excellent resource. (Thanks, Roger N1RJ)
Rebuilding antennas made of aluminum tubing often hits a snag when you're trying to clean out the inside of overlapping joints. Skinned knuckles, sore fingers, and a less-than-satisfactory result often result. When the topic came up on the TowerTalk reflector, Scotchbrite pads wrapped around a screwdriver and gun cleaning brushes were the most commonly mentioned tools. For loosening up any hardened lube or anti-oxidation compounds, WD-40, carburetor cleaner, or brake cleaner got glowing reviews (with a caution that rubber gloves and good ventilation are in order, particularly for cleaning solvents.)
TECHNICAL LINK OF THE Month - K0BG's Mobiling Web Site http://www.k0bg.com
73 W6IGK Elmer
