I'm not so convinced about this: "OMEGA was the primary means of radio navigation, world wide, from 1976 to 1997. ."
There was LORAN-C, after all. And Omega was a CW, phase difference system, LORAN a pulse system. AFAIK, Omega never really made it into the uP age; LORAN certainly did. -John =========== > The Helix coils are 25' high and have a 6' high relay: > http://www.haikuvalley.com/History/OMEGA-NAVIGATION-SYSTEM/8839335_kzKJLd#!i=2042047390&k=QJbHKzM/ > > > --marki > > > -----Original Message----- > From: time-nuts-boun...@febo.com [mailto:time-nuts-boun...@febo.com] On > Behalf Of Bob Camp > Sent: Monday, 29 July 2013 7:05 AM > To: Discussion of precise time and frequency measurement > Subject: Re: [time-nuts] GPS Spoofing > > Hi > > So in this case we're talking about "horrible" to "even more horrible" in > terms of efficiency. I'll freely grant that a 600' tower over a really > good ground plane (like say the sea) is going to be way more efficient > than anything I'd come up with. The same thing would apply to a matching > network made of coils you can stand up inside compared to anything I'd > make. > > Totally off topic - In the lobby of Continental Electronics they used to > have this typical transmitter sitting there. You sort of wondered "why". > After looking at it you figured out the little ant down in the bottom was > a person. Yes, the coils and "stuff" in Omega transmitters were *big*. > > Bob > > On Jul 28, 2013, at 4:23 PM, Tom Miller <tmil...@skylinenet.net> wrote: > >> You can't use "efficient antenna" and "100 kHz" in the same sentence. >> Oh, wait... >> >> >> ----- Original Message ----- From: "J. Forster" <j...@quikus.com> >> To: "Discussion of precise time and frequency measurement" >> <time-nuts@febo.com> >> Sent: Sunday, July 28, 2013 3:06 PM >> Subject: Re: [time-nuts] GPS Spoofing >> >> >> The point about the duty cycle being low is correct. And, there are >> commercial linear power amps, like the used ones made by ENI and >> others, that can easily put out 1 kW plus narrow pulses. >> >> Furthermore, the pulse generator is trivial to make with a Rb, 3 or >> more Tektronix DD501s, a simple OR gate and a gated oscillator at >> about 100 kHz. I've cobbled up that setup several times as a LORAN-A >> simulator. >> >> The main difficulty is getting a reasonable match to an efficient >> antenna at 100 kHz. >> >> -John >> >> ================= >> >> >> >>> Hi >>> >>> Since it's a pulse system, and you get to position your pulse for >>> maximum effect, I don't see any reason to generate CW power. Simply >>> mimic the lowest power slave in the chain. There's very little >>> redundancy with Loran, so spoofing one station will mess it up. No >>> need to mask the entire chain. At most you would need to hit two low >>> power slaves. >>> >>> Math wise: >>> >>> Wavelength is 10,000 ft / 3,000M. Throw things off by ~10% of that >>> and you have problems in a harbor. You would need to play a bit to >>> see weather a pulse every so often does the trick or not. Is that 20 >>> db below the slave or not ? You'd have to play with it. It's in that >>> range. A spoof that says they are on the other side of the world >>> isn't going to work. One that says you are on the north side of the >>> channel (when you are on the south side) is what would work. >>> >>> Power within a pulse set at a 5:1 duty cycle. For a 50,000 us GRI >>> you have another 50:1. For longer GRI's you might add another 2:1. >>> Net is a peak to average ratio of 250-1000 to 1. Put another way, a >>> 500W pulse is ~ >>> 1 average. >>> >>> Power at 100 KHz = what's in a fairly cheap switching power supply. >>> Plug it into the wall. A couple hundred watts (or even KW) pulse is >>> cheap. Say you have 120W out of the wall (or a car battery). If the >>> math above is correct and you can run 80% efficiency, that's a pretty >>> powerful pulse. >>> It's probably cheaper to generate something at 50:1 rather than the >>> whole >>> > 200:1. A 5KW is a *lot* of RF, even into a simple antenna. >>> >>> Antenna - there's a couple ways to do that. All of them are tradeoffs >>> (size / cost / power). The cheap way is to use a wire that's already >>> there.... Since you don't need to propagate (near field), the antenna >>> efficiency could be higher than you would think for some antennas. >>> >>> Is it easier than that with some smarts involved in the pulse - >>> probably yes. Do the smarts raise the hardware cost significantly? - >>> you'd have to build a few and find out. What really drives this or >>> that Loran receiver nuts? I'm quite sure you could work that out with >>> one to play with. >>> >>> Am I gong into the Loran-C jammer business? No, so don't contact me >>> off list to buy one. The point is not *have* I built one, but could >>> one be built easily. >>> >>> >>> Bob >>> >>> >>> On Jul 28, 2013, at 1:29 PM, "Poul-Henning Kamp" <p...@phk.freebsd.dk> >>> wrote: >>> >>>> In message <dab33aef-98ef-4503-89a7-657f0d25a...@rtty.us>, Bob Camp >>>> writes: >>>> >>>>> I'm not talking about taking out Loran-C over the entire North >>>>> Atlantic. >>>>> The target is a harbor sized area. For that, you certainly do not >>>>> need a 600' antenna or megawatts of power. >>>> >>>> No, you need about 600W (continuous) and a loop-antenna about 5m in >>>> diameter. >>>> >>>> Do the math, It's not as easy as you think. >>>> >>>> -- >>>> Poul-Henning Kamp | UNIX since Zilog Zeus 3.20 >>>> p...@freebsd.org | 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 -- time-nuts@febo.com To unsubscribe, go to >>> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts >>> and follow the instructions there. >>> >>> >> >> >> _______________________________________________ >> time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to >> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts >> and follow the instructions there. >> >> _______________________________________________ >> time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to >> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts >> and follow the instructions there. > > _______________________________________________ > time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. > > > _______________________________________________ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. > > _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.