[time-nuts] GPS Spoofing

J. Forster jfor at quikus.com
Sun Jul 28 18:24:30 EDT 2013


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-bounces at febo.com [mailto:time-nuts-bounces at 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 <tmiller at skylinenet.net> wrote:
>
>> You can't use "efficient antenna" and "100 kHz" in the same sentence.
>> Oh, wait...
>>
>>
>> ----- Original Message ----- From: "J. Forster" <jfor at quikus.com>
>> To: "Discussion of precise time and frequency measurement"
>> <time-nuts at 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" <phk at phk.freebsd.dk>
>>> wrote:
>>>
>>>> In message <DAB33AEF-98EF-4503-89A7-657F0D25AC48 at 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
>>>> phk at 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.
>>>
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>>
>>
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