Hi Well finding a +10 dbm 1.5 GHz transmitter isn't very hard to do at all. I've got several of those….
Bob On Oct 8, 2013, at 9:42 AM, Jim Lux <[email protected]> wrote: > On 10/8/13 4:17 AM, Bob Camp wrote: >> Hi >> >> But there's obviously something wrong with the 400 KM number. >> >> 1) If +10 dbm is good enough to burry a useful signal at that distance, it >> should be good enough to communicate at that distance. That's pretty >> impressive QRP without high gain / directional antennas involved. >> 2) The radios (at least the modern ones) do have CW signal immunity. Weather >> that's 60 db or something else probably varies with the make / model of the >> GPS. How well that works with a VCO jammer - again, a that depends sort of >> thing. >> 3) There's a (maybe) 40 db variation in GPS signals. To deny service you >> need to take out the strong ones, not just the weak ones. >> 4) Even without specific anti-jam in the GPS, the code it's self does have >> some immunity to a jammer. >> >> Of course you don't have to look very far into the archives to find >> wonderful examples of slipped decimal points in my posts…. >> > > > You're right, I forgot the process gain of the despreading. > Assuming you're going from 1 Mchip/sec for the C/A code to 50 bps for the nav > message, that's 43 dB > > That alone gets you to 2km jamming range from 400km, but that also assumes > that the jamming signal doesn't inhibit acquiring the code and despreading. > > As Dixon's book on Spread Spectrum says, "acquisition is the hard part"; > because you don't have the process gain yet. I suppose with a parallel > acquisition strategy, you're basically trying all codes, and that might be > able to work. > > But even so, those sorts of process gain arguments don't necessarily work if > the receiver has a hard limiter or quantizer in it. > > I don't know that modern consumer GPSes have CW immunity. If they're using a > 1 or 2 bit quantizer, a strong CW signal pretty much captures the front end. > > Easy to try. Let me just fire up my kilowatt 1.5 GHz transmitter here<grin> > > > > > _______________________________________________ > 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. _______________________________________________ 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.
