From owner-freebsd-current@FreeBSD.ORG Sun Mar 6 15:59:24 2011 Return-Path: Delivered-To: freebsd-current@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:4f8:fff6::34]) by hub.freebsd.org (Postfix) with ESMTP id E4424106564A for ; Sun, 6 Mar 2011 15:59:24 +0000 (UTC) (envelope-from erob@gthcfoundation.org) Received: from relais.videotron.ca (relais.videotron.ca [24.201.245.36]) by mx1.freebsd.org (Postfix) with ESMTP id BAD7A8FC0A for ; Sun, 6 Mar 2011 15:59:24 +0000 (UTC) MIME-version: 1.0 Content-transfer-encoding: 7BIT Content-type: text/plain; charset=ISO-8859-1 Received: from [192.168.0.100] ([184.162.50.38]) by VL-MR-MRZ22.ip.videotron.ca (Sun Java(tm) System Messaging Server 6.3-8.01 (built Dec 16 2008; 32bit)) with ESMTP id <0LHN00GUT8EZAY80@VL-MR-MRZ22.ip.videotron.ca> for freebsd-current@freebsd.org; Sun, 06 Mar 2011 10:59:24 -0500 (EST) Message-id: <4D73AF44.9070909@gthcfoundation.org> Date: Sun, 06 Mar 2011 10:59:00 -0500 From: Etienne Robillard Organization: Green Tea Hackers Club User-Agent: Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.9.1.16) Gecko/20101227 Icedove/3.0.11 To: Diane Bruce References: <4D7398C6.8030800@gthcfoundation.org> <201103061533.32138.hselasky@c2i.net> <4D73A085.4030009@gthcfoundation.org> <4D73A41A.4050109@gthcfoundation.org> <20110306153517.GA86035@night.db.net> In-reply-to: <20110306153517.GA86035@night.db.net> X-Enigmail-Version: 1.0.1 Cc: freebsd-current@freebsd.org Subject: Re: can somebody explains OFDM in FreeBSD? X-BeenThere: freebsd-current@freebsd.org X-Mailman-Version: 2.1.5 Precedence: list Reply-To: erob@gthcfoundation.org List-Id: Discussions about the use of FreeBSD-current List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Sun, 06 Mar 2011 15:59:25 -0000 . > https://gthc.org/investigations/OFDM/72_armstrong_ofdm.pdf > > That paper is a basic paper. COFDM is being used just about everywhere now. > OFDM was used in the Telebit modems of years gone by. To this day > (last I checked) it is superiour to the v32.bis format used today on > third world phone lines, because of its ability to ignore dead spots > in the frequency spectrums used. > > ... > Reference(s) please? >> I'm worried from a amateur computer scientist point-of-view about the >> harmfulness >> of EMF fields; in particular the ELF/VLF frequencies as defined in OFDM, >> for operating WLAN devices as 'ethernet-class subcarriers'.. >> > I personally would not worry about DSL and ethernet. The fields are > self cancelling due to the twisted pair. It's a transmission line. > I do worry much more about cell phone and wifi signals. I advise others > not to use cellphones for long periods of time without a remote earpiece. > (And of course, do likewise). Cell phone towers provided they are up high > enough do not bother me. Keep in mind the inverse square law here. > I would also suggest you look for the papers on double blind studies of > so-called RF sensitive individuals. (ES) I am very sceptical personally > of the effects. That said, I would not want to be within the near field > of any high power transmitter. This is why broadcast stations have > fences around their antennas and warning signs. The high power stuff > is dangerous. > > Its not phone lines who are the main issue, rather the radiation levels of OFDM ethernet class devices (including USB devices and routers) using ELF/VLF frequencies below 30khz as per the newer 802.11(ng) drafts... ;-) -- Etienne Robillard Company: Green Tea Hackers Club Occupation: Software Developer (and CEO) E-mail: erob@gthcfoundation.org Work phone: 450-936-2123 Website (Company): https://gthc.org/ Website (Blog): https://gthc.org/blog/ PGP public key fingerprint: F2A9 32EA 8E7C 460F 1728 A1A7 649C 7F17 A086 DDEC During times of universal deceit, telling the truth becomes a revolutionary act. -- George Orwell If a free society cannot help the many who are poor, it cannot save the few who are rich. -- John F. Kennedy