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In article , "Ryan, KC8PMX"
writes: I definitely am not an expert in any way, shape or form about this whole BPL thing, but to me logic would dictate that if these BPL lines are going to be emanating a ton of intereference, would they not also be prone to interference coming in??? Not necessarily. It depends on the format of the wideband information and whatever is used, if any, for error detection/correction, and whether or not that detection/correction is in the "up" or "down" direction along the lines. The problem in trying to decide anything about BPL is that NONE of the proponents are revealing anything about the technical characteristics of their various systems. None of us know the "weight" of the "ton of interference," not even the ARRL Lab. Seems to me that would create problems with connections and the quality of transfer rates. Ordinarily, with simple systems, yes. Case in point against: We (wife and self) decided on the digital cable TV service from our cable TV provider, main point being the larger number of non-fee channels available plus other services. That digital TV service provides "up" (to the head-end) communications through the supplied cable set-top box, used mainly for pay-per-view requests and the like. The analog TV service from the same provider requires telephone contact (tone-dial entry). Minor point, but the analog TV distribution is one-way and IS subject to external RFI affecting the signal. The digital TV distribution is very nearly interference-free on all channels and there are many more of those available in the same bandspace than can be had via analog TV distribution. The digital TV formatting is the major key in being interference-free...as well as holding video and audio quality consistent regardless of signal strength. I don't know for sure whether the digital TV format includes any error- correction capabilities in our particular TV cable provider but I suspect it does based on general electronics trade information of the past. "Broadband over Power Lines" is such a general term that no clue can be derived from the name or the bandwidth of the "broadband" part. If the BPL was carrying just a single Internet provider, then the bandwidth could be considerably smaller than the 78 MHz bandwidth referred to on 03-104, even for 1.54 MHz "T1" or equivalent digital service...in both "up" and "down" directions operating equivalent to full duplex. Irrespective of the bandwidth, there's no information on the lines' RF levels from various BPL proponents. Only one BPL system was indicated as wanting "Part 15" incidental radiation levels much higher than existing regulations. That still doesn't give any indication on what the BPL distribution system line levels are. Line levels of RF are important in considering the BPL coupling systems to provide subscriber drops...but there is NO information on what any of them use for couplers. We don't know for sure if they are really using the "MV" (4 to 12 KVAC, depending on locality) lines as long distribution lines. Those MV lines have finite lengths and we don't know if the BPL system provides any sort of terminations at RF of those ends. If there is no termination, then the lines will radiate as indicated in the ARRL model. Those MV lines can radiate even if terminated, although such radiation at HF will be lower. MV lines were NEVER characterized, standardized, or municipally-coded as RF transmission lines, not even in the National Electrical Code documents. Their lengths and wire spacings (especially above ground) vary considerably. They work very fine at 60 Hz, dependable and reliable as they are, whether elevated or underground. There are no details sufficient for any sort of real technical evaluation so all of it is a big guessing game at this point. The only true reports are the radio observations done at the BPL test sites, not done with calibrated field strength meters/receivers. LHA |
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