I think that when a GPS chip reports that there are no satellites found then you got a jammer or a tunnel!

At 07-10-2013, you wrote:

OK so let's say you have a receiver and detect a certain about of power at
the right frequency.  How do you determine which of three cases you have
(1) an actual GPS signal from a satellite. (2) a spoofer (who tries hard to
look like #1) or (3) a jammer.

You can't just go by the amount of power received because the
spoofer/jammer can have any amount of power because they can be at any
distance from you and the GPS satellites have variable power because of the
distance from the horizon.  I think you have to look at the signal itself.
You can scan a directional antenna to determine direction but you will get
many false positives when real GPS satellites are near the horizon.  You
would have to track the orbits of all of them.

Spoofers are a real problem.  A sophisticated spoofer tries very hard to
look like the real thing.  I think you would have to compare the position,
velocity and time you get from GPS with your known position, velocity and
time and if there is enough difference assume you are being spoofed.  But
again a good spoofer will create a subtle error.  For example if the
spoofer is protecting a building from GPS guided bombs it only needs to
create a 200 yard position error.  The spoofer may be tracking the location
of the falling bomb and may start by transmitting a GPS signal with no
error and then add more and more error so as to guide the falling bomb off
target.  This is actually how the some radar jammers work, they send out a
signal designed to be "believable" so that the guidance system in the
anti-air missile dose not detect that it is being jammed an simply goes off
target.    I think the only way to detect a sophisticated spoof is to have
multiple receivers with known relative positions.  A change in relative
position would indicate a spoofed GPS signal.

Jammers can be sophisticated as well the better ones will use a directional
antenna aimed at the target and will adjust their power output based on
distance to the target.  A truck driver likely would not use such a device.
A national military might deploy a very sophisticated GPS jammer as part
of an air defense system. It would by design be hard to detect.

So the easiest thing to detect would be a cheap, GSP jammer that is moving.
You could use multiple receivers to triangulate the location and then
determine it is not in orbit and is not a reflection from a metal roof or
something.    The problem is the jammer's very low power.  These things are
inteneded to only cover a tiny area

On Mon, Oct 7, 2013 at 7:46 AM, Collins, Graham CollinG@navcanada.cawrote:

--

Chris Albertson
Redondo Beach, California

On spacecraft hardware, even though something is a bit old, it does make
sense to use it.

Space qualifying a piece of hardware is very, very expensive, because it
requires a lot of shake and bake plus thermal vaccuum and other things.

Furthermore, there are always unknowns.

Do YOU really want to see a Billion dollar mission go wrong, because you
used a new, unproven, design of Cammand Receiver or Sequencer?

In my view, if you are going into the unknown, you want to use the best
available, tested and proven, stuff you can get whereever you can.

Remember, many of the launch vehicles still used were made in the 1950s or
1960s, and sat in a missile silo somewhere, as ICBMs for 30+ years. Until
fairly recently, the Atlas used sub-mini vacuum tubes.

I'm not against inovation, but it's not necessarily about saving a few
bucks when older gear is used.

YMPV,

-John

=======================

Hi Hal:

Yes you can detect jammers driving by.

There was a prior case of unintentional GPS jamming around Moss Landing harbor, Monterey Bay, California caused by a
faulty (oscillating) active TV antenna on a boat that was powered 24/7.

Military GPS receivers, like the DAGR or PLGR-II, include jamming detection.
http://www.prc68.com/I/DAGR.shtml#P2APPS

The patent Handheld GPS jammer locator
https://www.google.com/patents/US7233284
Contains some interesting info plus detailed plans for the hardware including mfg & model numbers, but not the Altera
Model EPM7064STC44-10 FPGA code.  I suspect the FPGA not only does what's required for the patent to work, but also some
other stuff like switching the LO to other frequencies (maybe both hi and lo side) so that it works not just for L1, but
also all the GNSS positioning frequencies.  But you could use a micro controller to do the same thing for a one off unit.

What was not mentioned in the TED talk was how a US UAV was captured pretty much intact by spoofing a military GPS receiver.

Have Fun,

Brooke Clarke
http://www.PRC68.com
http://www.end2partygovernment.com/2012Issues.html

Hal Murray wrote:

Yes, there is equipment out there today that can be used: UBlox offers jamming detection and level. We incorporated that into the later JLT products, and even made a special board for a customer that displays the GPS spectrum in real time showing the jammers in the frequency domain.

Bye,
Said

Sent From iPhone

On Oct 6, 2013, at 21:59, Hal Murray hmurray@megapathdsl.net wrote:

From: Jim Lux

So much for receiving signals from Transit at 400 MHz (<grin>) or from
Mars (The rovers relay through the orbiters in the 400 MHz band)

Jim,

Just get a FUNcube Dongle Pro (original version) instead!  There's a Yahoo
group where we often see those sold and bought.  Or use one of the DVB-T
dongles perhaps with a suitable pre-amp and filter.

Cheers,
David

SatSignal Software - Quality software written to your requirements
Web: http://www.satsignal.eu
Email: david-taylor@blueyonder.co.uk

On Sun, Oct 06, 2013 at 09:59:50PM -0700, Hal Murray wrote:

I would think this would be a natural task for one of the SDR

setups like the USRP and gnuradio... and using the more sophisticated
MIMO versions of the USRP and a suitable DF antenna array of GPS
antennas you could use correlation interferometry to get a pretty good
bearing on a passing jammer (no mechanical rotating antenna needed).
Use a couple of these in a suitable relationship to the road and you
probably could locate the vehicle in question and capture video of it.

Might be some quite interesting statistics near an interstate

with heavy truck traffic.

--
Dave Emery N1PRE/AE, die@dieconsulting.com  DIE Consulting, Weston, Mass 02493
"An empty zombie mind with a forlorn barely readable weatherbeaten
'For Rent' sign still vainly flapping outside on the weed encrusted pole - in
celebration of what could have been, but wasn't and is not to be now either."

On 10/7/13 10:44 AM, David J Taylor wrote:

Well, Transit is dead, as far as I know.. And the last person I know who
recorded the UHF signals from Mars used the 100meter antenna at Green
Bank.

Good to know though..

On 10/7/13 8:31 AM, Chris Albertson wrote:

The jammers put out many milliwatts and have enormous signals that are
obvious on a spectrum analyzer.  GPS signals are invisible on a spectrum
analyzer, normally.  IN fact, most GPS receivers don't work very well if
there are signals above the noise floor: they depend on the noise to
make them work with their mighty 1 bit quantizers.

I doubt anyone is selling spoofers on eBay.
Sure, one can probably find some  code to run on a USRP from some grad
student's project.

They are not designed with coverage area in mind.  They are basically
"whatever power the VCO puts out coupled to the antenna"  From a jamming
standpoint, they're not very sophisticated.

As a result they dump out something like +10dBm.
So running a quick Friis formula link budget, and assuming you want to
have a Prec of around -100dBm (10 MHz BW, kTB)

110 = 32+ 20log10(1575) + 20log10(d)
110-32 - 25 = 20*log10(d)
d = 400 km...

This is why they are such a problem

On 10/7/13 4:51 PM, David I. Emery wrote:

AN excellent project for a student.  You could make a nice senior
project or Master's thesis with this.