There are apparently multiple types of jammers. The swept VCO takes a lot of power and is really obvious. Feeding a noise source to a VCO takes the same power but is apparently a bit more stealthy. I'm seeing reference to a "chirped" type of jammer, which I assume takes less power? 
At the Institute of Navigation GNSS conference a few weeks ago, there was a whole track on interference and spectrum issues:http://www.ion.org/gnss/program.cfm
I haven't looked to see if they're available anywhere, but a good starting point might be to track down some of these papers:
Signal Acquisition and Tracking of Chirp-Style GPS Jammers: R. Mitch, M. Psiaki, S. Powell, B. O'Hanlon, Cornell University; J. Bhatti, University of Texas at Austin
A Novel Detection and Tracking Algorithm of Chirp Type Civilian GNSS Interference: C.H. Kang, S.Y. Kim, C.G. Park, Seoul National University, Republic of Korea
An Interference Monitoring System for GNSS Reference Stations: J. Wendel, C. Kurzhals, Astrium GmbH, Germany; M. Houdek, Iguassu Software Systems; J. Samson, ESA
-Nate B-
Bob Camp  wrote:
>                 Hi
> 
> Anything that will receive up there should be able to tell you when a jammer comes by. The issue is that not a lot of gear is made for that band (other than GPS receivers). The easy approach would be to use a modern GPS module that puts out noise level / jamming information. 
> 
> Bob
> 
> 
> On Oct 7, 2013, at 12:59 AM, Hal Murray <hmurray@megapathdsl.net> 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?
> > 
> > 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?
> > 
> > Is this something semi-geeky amateurs could contribute to?
> > 
> > What sort of gear has harmonics in the GPS band?
> > 
> > ------
> > 
> > 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.
> > 
> > 
> > 
> > -- 
> > These are my opinions.  I hate spam.
> > 
> > 
> > 
> > _______________________________________________
> > time-nuts mailing list -- time-nuts@febo.com
> > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
> > and follow the instructions there.
> 
> _______________________________________________
> time-nuts mailing list -- time-nuts@febo.com
> To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
> and follow the instructions there.
>                 