[time-nuts] ***SPAM*** How hard is it to detect a GPS Jammer?

[Jim Lux]

On 10/6/13 9:59 PM, Hal Murray wrote:
> The recent discussion of solar flares screwing up GPS timing was interesting.
>
> I just watched Todd Humphreys TED talk again.  He's focused on location, but
> does mention time in terms of stock exchanges.
>    Todd Humphreys: How to fool a GPS
>    http://www.ted.com/talks/todd_humphreys_how_to_fool_a_gps.html
>
> He's got a good discussion of GPS jammers and spoofers, but no geeky details.
>
>
> What's the spectral/power output of the typical eBay GPS jammer?

There were a series of articles in GPSWorld last year(?) that described 
test on some jammers.  For the most part, swept VCOs, as I recall.


>
> Suppose I lived near a major highway.  Could I build a receiver that would
> count jammers driving by?  Could I track them (at least somewhat) with a
> directional antenna on a rotator?

Yes..
Or do what real sigint receivers do, use multiple antennas less than a 
have wavelength apart and interferometry to do direction determination.


>
> Is this something semi-geeky amateurs could contribute to?

Yes, but more in the long term policy sense. you could measure the data 
and publish a paper saying "here's what the jammer incidence is".

It's not like you could say "I detected a jammer, and it appears to be 
coming from license plate ABC 123".  I suppose you could send such data 
to the FCC, but I don't know that they have a good ingest mechanism.


>
> What sort of gear has harmonics in the GPS band?

Poorly operating TV antenna booster amplifiers are notorious, as are 
some plasma flat screens.


>
> ------
>
> I assume people are familiar with the trucker who jammed the FAA test in NJ.
> Here is a good story:
>    http://www.insidegnss.com/node/3676
>
> That article has a link to commercial gear targeted at this market.
>    http://www.exelisinc.com/solutions/signalsentry/Pages/default.aspx
> The graphics shows 3 receivers is a port/harbor setting.
>
>
>