AVR Freaks

metron9 is best of by telling that it cannot be done.

even though it can all be done, it is illegal to do (lets forget the potential steeling of a car).
I think that you will run into major problems when jamming the GPS signal. this is more or less a very crucial thing used by the US military, and lets not forget indeed car trackers. I think that purposely jamming that or even making a jammer will make you an enemy of the state...

It should be possible to pick up the local oscillator of the GPS receiver at 1575.42MHz +/- its IF frequency.

You can jam any radio, no matter at what frequency it is tuned at, by transmitting at the commonly used IF frequencies, like 455KHz or 10.7MHz.

Metron9's friend was asking if there was a detector to sniff out a GPS that may be located in a car. Nothing about it "protecting" the car, nor about jamming it.

A paranoid person might be concerned that such a GPS unit had been secretly attached to a car, for example by a suspicious spouse, the FBI, or who knows who. If the placer didn't have physical access to the vehicle to recover it later with a recording of where it had been, the unit would continuously transmit its location, probably as a cell phone signal, and could probably be detected easily enough as it signed on when the car started to move. It probably wouldn't take anything very sophisticated - my computer speakers pick up interference from my phone when it checks in every hour or so.

The friend didn't ask Metron9 about jamming it, only about detecting it. I was responding to the friend's question, not Metron9's. Perhaps I'm too literal for my own good sometimes.

There is one way. And telling about it is not even dangerous.

Go to the nearest EMC lab that has a shielded room large enough to drive the car into. There's a place not too far from where I live that has(had) one that could take a leopard tank.

Sitting close to the shielded room you will find an abysmally expensive measurement receiver.

Start the car. First check for the typical oscillator frequencies that GPS receivers use as clock. 18.414 used to be one. Locate each clock oscillator with a sniffer antenna.

Have the technician write a report, sign it, and pay the bill.
Done.

/Kasper

Edit:
As a side note, at least here, expensive car brands are sold with gps trackers without the owner's knowledge. When the car is then stolen, the insurance company can buy access to the tracker.

If you are close enough, it's possible to detect the GPS Receiver's first local oscillator. Ussualy the tracking devices send data through GPRS so it can be detected

Hi, metron9,

"if there was a detector available to sniff out a GPS that may be located in a car."

I measured oscillator reradiation, which might be good for detection.

The device under test used
a) a direct down converting mixer, where the oscillator frequency leaks best to the receiving antenna.
b)no preamplifier. Using one was my suggestion to reduce the oscillator reradiation. But preamplifer will not block the signal, only attenuate it.

But different vendors of GPS-Rx might use different concepts. You will have to test some with a spectral analyzer.

Ciao
Wolfgang Horn