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From: John Smith on Tues 9 Aug 2005 17:46
Len: The BPL modems I have seen go from the bottom of low audio freqs up to ~300Khz. I don't know where anyone ever got the idea this range was even going to go into the am broadcast band! At some of those freqs, a full wavelength can be measured in miles... and, the "transmission line" becomes a few small wavelengths... We aren't talking about the in-building carrier-current kind of thing. This is HIGHER SPEED stuff occupying HF and on up to about 80 MHz. I think they are doing, REALLY, what they say they are doing, they are now simply in the process of TESTING it, what the final results of all this are/"will be" ??? It's primarily MARKET testing...plus ordinary Field Trials. Seems to be very difficult to get some real guts-contents kind of information but it IS broadband, much wider than the best carrier-current stuff. There's been several field tests for RFI on the installed Test (Market) locales. That Testing began 3 years ago or so. It has gone on longer in Yurp. You can begin looking into BPL at the ARRL website and continue on to some very large RFI testing reports by the government and private metrology companies, checking out the links. FCC ECFS has lots and lots and lots of Comments on it. Much of that has been thrashed-out in words and figures in 2003 and 2004. I am just stating amateurs and the interference it MAY pose to their HOBBY is NOT ANY REASON(S) to be given ANY consideration what-so-ever, it is not the majority--the greatest good for the greatest number... The "majority users" of HF may NOT be just radio amateurs. Aeronautical Radio Inc., ARINC, contracts to do HF comms with air carriers on long international routes. Those sites CAN be interfered with, not a good thing with the "heavies" (747 and the like) carrying lots of passengers. The U.S. government has about 2500 HF-capable stations in the contiguous states, AK, and HI, plus PR and other U.S. territories. Those are periodically netted as a SHARES exercise. Most of those are equipped with ALE and can jump frequency as needed depending on local QRM. There's still a couple of low HF freqs for maritime emergency comms. Maritime radio services still use HF especially on deep water; they've gone to single-channel SSB for voice and Teleprinter Over Radio for data in place of electromechanical teleprinter. There's the WWV and WWVH time-frequency standard stations; not everyone uses (or can get) the 60 KHz WWVB signal; still useful for medium-accuracy metrology. The "low-VHF" band for PLMRS (Private Land Mobile Radio Service) includes freqs in high-HF as well as from 30 to 50 MHz. Lots and lots of those still working in USA. "SW BC" can kiss some of their audience goombye wherever a BPL is running since it will effectively mask reception of both foreign and domestic stations. There are more SW BC bands than there are ham bands on HF. The "occupiers" of HF can be found at the NIST site as reports and documents, going back two decades if you like that sort of thing. They and the NTIA work together to try future planning for the EM spectrum; FCC cooperates by using that information for decision-making on specific radio services. FCC OET (Office of Engineering and Technology) concentrates on Mass Media radio services (broadcasting) for BC standards, separation of stations by locale, and useful info on BC antennas. In Yurp there's similar but their "BPL" (they use another acronym) is older. The first system was a test in Norway. Lots of info on the web for that, just not concentrated neatly as for the USA. Japan has done some trials and was NOT happy with the results. Ackshully, the electric power transmission people have been using a BPL-predecessor longer for telemetry and control of the power lines they are controlling. Slower-speed stuff which may be what you've seen. Hasn't been a bed of roses for them, either, according to some of the Commentors in the FCC ECFS on Access BPL, a couple of those being P.E.s who were involved in that "pre-BPL" work. Electric power folks have the advantage that few other folk live close to the Kilo- and Mega-Volt electric power transmission lines; them MVe lines be ten kinds of noisy anyway. Access BPL systems in Market Testing have been using the "medium" (around 4 KV) distribution lines. Those are the ones that connect to transformer primaries (such as on utility poles) so that the secondaries can supply 230/115 Volt drops to individual subscribers. Some kind of couplers manage to get the KV line data to the drop lines for residential broadband service (two-way) with most systems but at least one uses a WiFax-kind of coupler to get to an individual residence. That sort-of isolates the data line from the KV. WiFax is a low end of microwaves or high UHF. I would presume that the data rate of these BPL providers is similar to the broadband data supplied through wideband cable such as TV cable service. TV allows HF to 50 MHz for broadband data downstream since it doesn't interfere with present-day TV channel 2; that's a 40+ MHz wide path for fairly-good-rate data. TV itself uses about 1 GHz bandwidth (give or take) for analog TV; larger for digital TV through fiber optic main distribution (analog for the drops). "Discontinuities" in transmission lines (for RF, data, etc.) are the culprit for high VSWR and thus reflected power which winds up spritzing out into space (around the lines). Discontinuities come from everything...jump to a different characteristic impedance, changes in conductor wires, weird loopy jumpers, pole-mounted circuit breakers. The electric power lines were NEVER characterized as RF or DATA transmission lines...ONLY for 60 Hz AC, never higher in frequency. rfi emi |
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