Various not so random notes: The power needed to jam GPS depends a lot on receiver state, during TTFF it takes virtually nothing.
Therefore most "real" jammers will periodically blast at high power, to "dislodge" any locked receivers and then continue at low power to keep them off the signal. They are also built spectrum efficient, by emitting a signal designed specifically to interfere with GPS' spread-spectrum encoding, either by trying to lure the receivers to aim for the jammer (lowest power) or just by mimicking the worst kind of power for acquisition & tracking (higher power). Most receivers have hard-limiting inputs, so overload is a slightly more involved concept than for analog inputs, but it is still possible. The jammers which were quoted earlier are not "real jammers": they are just simple noise-sources, and long range is a negative sales parameter, because they are intended for "personal protection": a long range would increase the risk that they get detected. Their main customer base is drug-runners, fraudulent businessmen, infidel husbands and criminals sentenced to home-confinement with a GPS a ancle-bracelet. Many of those jammers does not work as well as advertised. Some of them are even "trojaned" and emit a signature signal for the benefit of law-enforcement. The infamous tv-preamp case was so efficient because it trippled the frequency of a local TV signal, due to instability, went into saturation/clipping and had a circular antenna with convenient dimensions to radiation of the resulting blanket of noise around the GPS frequency. Unfortunately, nobody tought about measuring its power-consumption or if they did, they didn't publish it. Given the kind of UHF transistors usually used in antenna-preamps, we are very likely talking no more than 1W. I an urban/hi-rise environment, havoc can be played with jammers that use glass facades as reflectors for the signal. The story about the "Mexican LORAN-C jammer" is instructive in how that complicates finding the trouble. GPS antennas on planes in the air do receive some help from being above it all, and pilots can still fly without GPS. The trouble starts once CATIII landings on GPS become routine. Poul-Henning -- Poul-Henning Kamp | UNIX since Zilog Zeus 3.20 [email protected] | TCP/IP since RFC 956 FreeBSD committer | BSD since 4.3-tahoe Never attribute to malice what can adequately be explained by incompetence. _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
