Developed for GBPPR's Directorate of Operations case officers operating out in the field, this device uses a neat little trick to jam most of the common cellular modem (CDPD or analog AMPS) controlled GPS tracking devices.
First, a custom cut Fox 225.06 MHz clock oscillator is filtered with a 1575 MHz GPS bandpass filter isolating its 1575.42 MHz 7th harmonic. This harmonic is further amplified and sent to a small, low cost, surface mount antenna. This produces a limited range continous wave (CW) jammer centered on the GPS L1 frequency.
This jammer only has an effective range of a few meters and only jams the lower-cost standard positioning service (SPS) GPS receivers.
Second, a common 45 MHz clock oscillator drives the local oscillator port on a Mini-Circuits mixer. The RF & IF ports and connected to two small, low cost, surface mount 800 MHz antennas. Here's the trick, any cellular phone that attempts to call out is "jammed" by its own signal! This works because the phone's transmit and receive frequency are always separated by 45 MHz.
Example: your phone transmits on 837 MHz and receives at 882 MHz. If you were to mix the 837 MHz transmitted signal with a 45 MHz signal, the new mixer output frequency would be 882 MHz - and the phone would essentially jam itself.
This is very useful against "burst" tracking devices which may record your movements for a week or so at a time, then wait until 3 A.M. when your sleeping to burst out a quick phone call to KGB headquarters to upload the tracking data. It also prevents any computer record of phone calls or RF direction finding of the phone's signal from revealing your location.
This jammer also only has an effective range of a few meters (if that) and only jams analog AMPS cellular phones or CDPD modems.
This jammer should also work on the General Motors' (GM) OnStar Navigation System. The unit I saw utilized an old Motorola AMPS phone for communication.
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