Date: Tue, 23 Jan 2001 09:09:04 +0000 (GMT) From: Terry Lambert <tlambert@primenet.com> To: dmlb@dmlb.org (Duncan Barclay) Cc: tlambert@primenet.com (Terry Lambert), keichii@peorth.iteration.net, brad.knowles@skynet.be ((Brad Knowles)), kris@FreeBSD.ORG ((Kris Kennaway)), freebsd-chat@FreeBSD.ORG, grog@lemis.com ((Greg Lehey)) Subject: Re: GSM vs. CDMA (was: VCD (was Re: cvs commit: src/sys/dev/ata Message-ID: <200101230909.CAA15826@usr08.primenet.com> In-Reply-To: <XFMail.010123082809.dmlb@computer.my.domain> from "Duncan Barclay" at Jan 23, 2001 08:28:09 AM
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> > 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. Yep; exactly. It sucked a lot of juice, and the juice had to go somewhere. I was really surprised to learn that the receivers tended to take more energy than the transmitters, when you weren't trying to transmit huge distances. Now the PAL contingent will claim that it only interfered because we had an NTSC television. 8-) 8-). > 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. I think we're back to buying two phones, or using the "velcro" approach... > > 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. Actually, I believe several southern states in the U.S. use (or used) radar detector detectors, which if found, got you an "obstruction of justice" charge and a stiff fine. I know that for a while, until they were forced off the market, the FCC was trying to crack down on Radio Shack scanners, which could be modified (wire cutter out a diode) to remove the band filter for analog cell phone eaves-dropping. Much less of a problem these days, since it takes slightly more expensive equipment to listen in on newer cell phones. > > 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? They are professionally anal, which is probably what you want, given their job description. 8-). Actually, I'd expect them to be very defensive of their radio spectrum; look at what it took to pry the 2.4GHz for 802.11b and Bluetooth away from the French military... if nothing else, they could be happily out to confiscate European phones, for being put on their frequencies in the first place as a means of protecting Euro manufacturers from U.S. competition. Seriously, unless they were conducting electronic warfare exercises, I wouldn't expect them to notice, but I don't know what that frequency is used for when they do use it (The general's wife's walkie talkie? Very low energy short range communications that could be noticibly disrupted by a receiver on the frequency, the way LC tank door-security cards get read by RF readers? A private GSM system used only by the military, and completely compatible with European GSM phones? Klingon disruptors?). Terry Lambert terry@lambert.org --- Any opinions in this posting are my own and not those of my present or previous employers. To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-chat" in the body of the message
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