I was unaware of the context in which the far field question was raised. I don't know much about BPL, but if the control is to be exerted on the field radiated from the power lines in one's home, then my opinion is that antenna factor is the least of your concerns. Your real concern is not the receive antenna, but the transmit antenna, which is very long, of uncontrolled impedance and unmatched as well. At one or even three meters you will always be in the near field of the transmit antenna, so carefully controlling the receive antenna is wasted effort. Now you could certainly idealize the transmission line for the purposes of a standard test, and you would need to, but if you do that, why not specify and measure the BPL current on that matched transmission line? That can be done accurately, and the current limit on that matched transmission line can be derived from the sensitivity of that amateur band radio or other sensitive receiver operating in-band to BPL. That calculation can be done to two decimal places, ignoring uncontrollable sources of reflections. And you don't need a high-priced anechoic chamber for the test, either, just a screen room or area quiet enough that ambient fields coupling to the transmission line do not couple currents near the specification limit.
> From: "Iain Summers" <[email protected]> > Date: Mon, 7 Aug 2006 23:22:02 +0100 > To: <[email protected]> > Subject: Fw: Near field/Far field what is D. > > Resent without attachment - sorry forgot the firewall rejects GIF files. It > was a graph that shows all of the differing compliance levels and they are > as much as 60dBuV/m apart. If anyone wants it I can send it to their > individual mailbox. > > > ----- Original Message ----- > From: "Iain Summers" <[email protected]> > To: <[email protected]> > Sent: Sunday, August 06, 2006 4:30 PM > Subject: Re: Near field/Far field what is D. > > >> Gents, thanks for all of the comments so far. >> >> Ken exactly as you have stated regarding how antenna factors are produced >> is >> one of the issues that I am trying to bring to the fore for powerline >> telecommunications (PLT or BPL in the US). The current papers being >> circulated are not that helpful to either those for or against PLT. >> >> The problem at present is that CISPR 22 (or its European derivative) does >> not really deal with radiated emissions below 30MHz and in any case the >> location of measurements is going to be in a housing estate which is not >> well defined. Those that are trying to produce a standard are trying to >> come >> up with common acceptance limits for Radiated Emissions based upon >> existing countries >> standards. (see attached small gif file) >> >> The issues are that existing standards: >> >> A. Measure at different distances >> B. Use different detectors >> C. Measure different quantities, H, E (H converted to E assuming 377ohms) >> >> The common consensus appears to be that you measure with a loop and then >> convert to E using 377ohms. The problem is that when these results are >> published opponents argue that their services will be affected because >> they >> can extrapolate to a certain distance and their receivers are sensitive >> enough to detect this extrapolated value. The HOWEVER as far as I am >> concerned is that these values are so inaccurate initially that it is >> futile >> to try and make this case on a few fronts: >> >> A. field impedance is not 377ohms at 1 or 3 m (where most measurements >> take >> place) >> B. the antenna calibrations may not have been completed at 1 or 3m >> C. the attenuation with distance may not be 1/distance. >> >> I have measured C, I cannot control B and I am trying to get a feel for A, >> hence my initial question about 2D^2/lambda. >> >> Ultimately I am going to conduct some subjective mutual interference >> measurements to come up with some answers but not to 2 decimal places - >> that's for sure. >> >> Regarding modelling I was intending to produce some NEC models myself of a >> single dwelling but even a single ring main electrical circuit is >> difficult >> to model because its overall dimensions are large (64m^2 in my house) but >> it >> has 2 conductors lying about 5mm apart with an earth(in the UK) running >> down >> the centre. I am looking into it and will (with David Cuthbert's help) may >> come up with an extremely idealised solution. I'd like to understand the >> field changes for changing mains impedance which can be anything from 15 - >> 200ohms according to research. >> >> Cheers, >> Iain >> >> >> >> >> > > - > ---------------------------------------------------------------- > This message is from the IEEE Product Safety Engineering Society > emc-pstc discussion list. Website: http://www.ieee-pses.org/ > > To post a message to the list, send your e-mail to [email protected] > > Instructions: http://listserv.ieee.org/request/user-guide.html > > List rules: http://www.ieee-pses.org/listrules.html > > For help, send mail to the list administrators: > > Scott Douglas [email protected] > Mike Cantwell [email protected] > > For policy questions, send mail to: > > Jim Bacher: [email protected] > David Heald: [email protected] > > All emc-pstc postings are archived and searchable on the web at: > > http://www.ieeecommunities.org/emc-pstc > - This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. Website: http://www.ieee-pses.org/ To post a message to the list, send your e-mail to [email protected] Instructions: http://listserv.ieee.org/request/user-guide.html List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Scott Douglas [email protected] Mike Cantwell [email protected] For policy questions, send mail to: Jim Bacher: [email protected] David Heald: [email protected] All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc ______________________________________________________________________ This email has been scanned by the MessageLabs Email Security System. For more information please visit http://www.messagelabs.com/email ______________________________________________________________________
