Date: Tue, 23 Jan 2001 08:28:09 -0000 (GMT) From: Duncan Barclay <dmlb@dmlb.org> To: Terry Lambert <tlambert@primenet.com> Cc: keichii@peorth.iteration.net, (Brad Knowles) <brad.knowles@skynet.be>, (Kris Kennaway) <kris@FreeBSD.ORG>, freebsd-chat@FreeBSD.ORG, (Greg Lehey) <grog@lemis.com> Subject: Re: GSM vs. CDMA (was: VCD (was Re: cvs commit: src/sys/dev/ata Message-ID: <XFMail.010123082809.dmlb@computer.my.domain> In-Reply-To: <200101230748.AAA14547@usr08.primenet.com>
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On 23-Jan-01 Terry Lambert wrote: >> >> Yes, I saw that. I was more thinking about who you would be >> >> pissing off if you turned one of these things on in the U.S. >> >> near a military base. >> > >> > Hmm. Yes, I wonder what would happen. I wonder how long it would >> > take them to work out what was going on. >> >> A GSM phone will not transmit anything until it find a beacon being >> transmitted by a basestation. There is a scanning procedure that >> looks at all possible frequencies in use by all GSM networks (in a >> given band), followed by a timing acquistion, followed by reading >> of various informational packets transmitted in the beacon. The >> whole procedure is documented in the GSM 05.08 and 05.10 standards. >> >> The US military would not know anyone was using a phone because the phone >> would just not do anything apart from saying "no network". > > When I was in about third grade, I had a ham radio receiver (I > collected broken electronics and other things, which I would then > fix or scavenge for parts; I built my first robot in fifth grade). > > One interesting effect that I quickly latched onto to get PBS > programming on the television instead of "The Brady Bunch" > was that you can use one receiver to selectively jam specific > frequencies from being usable by another (if you tell my > sisters, I will, of course, deny this). All it takes is a > strong receiver (actually, when they make you turn off your > electronics in a plane, it's to keep them from interfering > with the on-board ILS receivers, not just so people will actually > use the GTE "AirPhone"). WTF is a "strong receiver"? I think that you are talking about local oscillator leakage that can be used to jam another signal. This effect is well known and handsets have to pass particular limits before being deployed. The emission limits for GSM handsets for Local Oscillator radiation whilst in receive mode are listed in section 4 of the GSM 05.05 standard and they specify a maximum emission of somewhere around -40dBm for a spurious signal. Because of the way one designs a GSM radio, this limit is really easy to beat unless you are using something called a homeodyne or zero-IF radio. Ironically, it is just these radios that will be used for multie-mode GSM/3G handsets. In about three hours I have a meeting on just with topic with one of our clients. > The point is, if the British can detect unlicensed televisions, Via detecting the radiation from the scan coils. A very strong signal, a couple of hundered volts at 15 odd kHz. > I think the U.S. Military can find a cell phone that looks > like a scanner trying to listen to their frequencies. Maybe they can, but a cell phone is certainly not a scanner. The GSM handset will complete its scan for basestations in about 30seconds and then go quiet. Do you think they really care? > Terry Lambert > terry@lambert.org Duncan --- ________________________________________________________________________ Duncan Barclay | God smiles upon the little children, dmlb@dmlb.org | the alcoholics, and the permanently stoned. dmlb@freebsd.org| Steven King To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-chat" in the body of the message
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