[time-nuts] GPS jamming susceptibility

[jimlux]

scmcgrath at gmail.com wrote:
> The Phrack article's jammer attacks the offset frequencies.
> 
> Phrack.org/issues.html?issue=60&id=13
> 
> This article shows just how vulnerable L1 GPS is
>

I'm not very impressed by design...
That old Freescale/Motorola MC145151 PLL, and using a separate 
prescaler?  That's a 1970s-1980s design out of some old ap note. Can you 
even buy a 145151 anymore? I suppose you can, there's probably millions 
of them out there in all manner of radios.

Why not get an eval board for one of the plethora of MMIC PLLs out there 
that has VCO, dividers, etc. all on one die.  Heck, NS has a whole 
webbench application that will basically design the thing for you.


On a related note... What about a GPS signal simulator.. Yes, there are 
commercial vendors out there who will be happy to sell you one for many 
tens of $k.. how about something simpler?  Seems it should be easy to 
have a FPGA programmed up to generate all the PN codes and nav messages, 
and just run it out to a mixer with a 1575 MHz LO (generated by one of 
the aforementioned $100 NatSemi eval boards)..

Or is it too much of a pain to do the doppler?  That would take 
something like an DDS to create a reference for each S/V simulator, with 
the DDS programmed for the required doppler.  So it would take N 
channels to do N S/Vs in view.  Yeah... the multi $10k starts to seem 
reasonable now..

I was sort of hoping, in the back of my mind, that some grad student out 
there had created some FPGA code to run on a Xilinx eval board (or a USRP2)