Tune the probe to resonance at the frequencies you know the receiver
use internally, and to the harmonics and sub-harmonics thereof. You
can also sweep tune the probe with the X axis sweep from the SA or
receiver so that the tuning of the probe tracks the frequency being measured.
You can also use a "GPS Jammer", or noise diode, bandpass filter and
amplifier, to saturate the vehicle with energy within first the GPS
bands, and then on the cellular bands, while you observe the
harmonics of these bands on an spectrum analyzer. If you time gate
the sweeps between the noise diode and the SA you can determine how
many inches away the GPS device is located based on the delay between
the stimulus leaving the signal generator and the GPS unit coughing
on a harmonic.
You can sometimes also get lucky by jamming all the cell phone bands
on the tower to base frequencies for at least 15 minutes, watching
the base to tower frequencies, then turning the jammer off to see if
the base-to-tower frequencies light up. This can only be done though
in cases where such jammers is legal, or in cases where you can
ensure that the signal is fully contained in the
building/garage/trailer you are using for the sweep.
Note that I would suggest that other do this, but some sweep firms go
out to a sterile location several miles away from their clients site,
and pickup the vehicle to be swept with an enclosed trailer or
flatbed. When they arrive they place a half dozen GPS and Cell phone
jammers throughout the vehicle to be swept, load the vehicle on the
truck, and haul it to a shielded garage to unload it (easy to do with
luxury sedans). Once the test vehicle is secure, and all the garage
doors sealed back up, the test instruments are powered up, and the
jammers are turned off one at a time to see if the tracker tries to
call home. Then the sweeper simulates a cell phone site to see if the
phone is in passive mode, etc, etc, etc..
-jma
At 09:29 PM 6/10/2007, Thomas Shaddack wrote:
>The GPS receivers use an intermediate frequency at 4.092 MHz. This, and
>its harmonics, are likely to be found in the GPS receiver's parasitic
>emissions.
>
>16.368, and/or 16.3676 or 16.367667 are crystal oscillators frequently
>found in GPS receiver units.
>
>The modulation frequency for the carrier wave is 1.023 MHz.
>
>A narrow-band high sensitivity receiver may be a help here. There are some
>frequencies inherent for the system, and unless the receiver is
>specifically designed for low emissions at these, it is likely to radiate
>predictably.
>
>Is this helpful?
>
>
>
>On Sun, 10 Jun 2007, Paolo Sfriso wrote:
>
> >
> > Dear Collegues.
> >
> > Would you know if there are any dedicated GPS receiver detectors
> (secondary radiation detector ?) that could be used for sweeping an
> automobile (where the use of a NLJD would be unrealistic due to the
> presence of a large number of legitimate electronic circuits) and
> stripping the vehicle to the bone is not an option ?
> >
> > Of course, the instrument would have to be tested and
> trustworthy, not some spystore gizmo...
> >
> > Kind Regards.
> >
> > Paolo Sfriso CFE
> > Director
> > GRUPPO S.I.T.
> > Security, Investigations & Technology
> > Quarto d'Altino, Venice
> > ITALY
> >
> > Phone +39 0422 828517
> > Fax +39 0422 823224
> > 24hr GSM Cell +39 335 5257308
> > www.grupposit.com
> > pauls..._at_tin.it
> > in..._at_grupposit.com
> >
> >
> > >
> >
>
>
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Received on Sat Mar 02 2024 - 00:57:22 CST