[time-nuts] GPS backup for the stationary time and frequencyuser

jimlux jimlux at earthlink.net
Sat Oct 9 15:22:28 UTC 2010

Matthew Kaufman wrote:
>  On 10/9/2010 8:00 AM, Magnus Danielson wrote:
>> Hmm. Yes. Creative! Once demonstrated essentially all WAAS/EGNOS/SBAS 
>> sats need to develope some protective measure.
> Unless, of course, such protective measures already exist. I can think 
> of several ways right off the top of my head... one would be to have the 
> transponder be able to shut itself down if it doesn't appear to be 
> relaying a single valid code stream... another would be to have ensured 
> that the maximum power density was low enough that anything with enough 
> real satellites in view couldn't be practically interfered with... 
> another is to have ground-based monitoring and a transponder enable 
> system that can't simply be jammed into the "on" mode but rather 
> requires a key be sent require regularly to keep the transponder powered 
> up...

that would assume that the WAAS transponders are actually purpose 
designed, and not just a generic bent pipe that was repurposed from 
something else.

If it's purpose designed, it's easy.. the uplink signal doesn't have to 
look anything like the downlink signal. You could, for instance, send up 
two signals which have to be combined on board to make the downlink signal.

For the initial WAAS, they may have just leased transponders that 
already existed..  which would be vulnerable, after a fashion.  There 
are a variety of AJ measures taken by the satellite operators (no more 
Capt. Midnight stuff)

> I just haven't seen anything in the literature noting that the threat 
> had been looked at and/or addressed in any way.

Unlikely that this would be in the open literature.  It's pretty clearly 
one of those things that falls under export control.

>> To pull it off, a standard GPS simulator and some minor frequency 
>> conversion is needed. Should not stop the handy man.
> Indeed.
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