[time-nuts] GPS jamming susceptibility

Bob Camp lists at rtty.us
Tue Nov 23 01:38:19 UTC 2010


Hi

If you run through the article the author claims that he's getting a few hundred feet of range with a few hundred mw of power into a good antenna.

Your cell phone and FM broadcast radio are equally susceptible under typical conditions. 

Bob

On Nov 22, 2010, at 8:24 PM, 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
> 
> Scott
> Sent from my Verizon Wireless BlackBerry
> 
> -----Original Message-----
> From: Magnus Danielson <magnus at rubidium.dyndns.org>
> Sender: time-nuts-bounces at febo.com
> Date: Tue, 23 Nov 2010 01:29:56 
> To: <time-nuts at febo.com>
> Reply-To: Discussion of precise time and frequency measurement
> 	<time-nuts at febo.com>
> Subject: Re: [time-nuts] GPS jamming susceptibility
> 
> On 11/23/2010 12:19 AM, Bob Camp wrote:
>> Hi
>> 
>> There is *very* little signal hitting the ground from a normal GPS bird. Even a few mili watts close at hand is going to be an enormous overload. The typical GPS does not use a lot of bits in the front end A/D.
>> 
>> I suspect that if you tuned your little gizmo down to the FM broadcast band, it would take out your favorite FM station quite nicely. Same would be true of your cell phone if you tuned it there. Jamming from close by isn't all that hard to figure out, or to implement. There are switching power supplies that make wonderful jammers for low frequency signals. If it's RF, it can be jammed. The real question is can you jam it from a reasonable distance?
> 
> There are a few reports and articles going into the susceptibility of 
> civilian receivers to jammers. Some public texts have also been written, 
> so the field is not completely covered only on green paper.
> 
> A CW jammer will basically grab the AGC and as it gains down the CW the 
> GPS reception is gained down with it. In particular 1-bit receivers is 
> susceptable to this effect. 1,5-bit receivers with separate AGC 
> detection was developed and was able to combat the CW jammer situation.
> The relative time when the code can control the bits quickly becomes 
> just a fraction since a sine spends long times in the extremes far away 
> from detection limits.
> 
> Next thing to attack is lack of supression in the C/A code, and list of 
> offset-frequencies which is more susceptible can be found.
> 
> Noise jammers is also possible.
> 
> Things like these alongside the weak signal makes civilian receivers 
> quite sensitive, so quite a bit of line-of-sight distance can be jammed 
> with a fairly low output.
> 
> Cheers,
> Magnus
> 
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