Simple 800 MHz Cellular Phone Jammer


This is a simple little 800 MHz band cellular phone jammer which can be easily built from commonly available parts.  Most homebrew cellular phone jammers are based around a sweeping RF oscillator which, while more "jamming" efficient, can be quite difficult for the beginner to construct without access to expensive RF test equipment.  This project can also be used to help take the load off certain people who receive 15 million emails a day from strangers asking them how to build their own cellular phone jammers...

This cellular jammer is based around a common 45 MHz clock oscillator driving the Local Oscillator (LO) port on a Mini-Circuits ADE-1ASK mixer.  This LO signal also passes through a simple impedance matching network to transform the high impedance of the clock oscillator down to the mixer port's 50 ohm impedance.

The mixer's RF port (RF input) is connected directly to a 800 MHz band cellular phone antenna, and the IF port (RF output) is sent to a Mini-Circuits VNA-25 MMIC amplifier which increases the output jamming power by around 16 dB.  This is then sent onto another 800 MHz band cellular phone antenna.

Here's the theory of operation...  Any cellular phone that attempts to call out is immediately "jammed" by its own signal!  This works because every 800 MHz band cellular phone's transmit and receive frequency are always separated by exactly 45 MHz.

Example:  Say your cellular phone is transmitting at 837 MHz and receiving 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 be jamming itself by "hearing" its own signal.  This appears to work quite well on most cellular phones and should also work on full-duplex Nextel transmissions.

These types of jammers are also useful for defeating cellular-based vehicle tracking systems which record your travels via GPS then "burst" out a phone call in the middle of the night.  It should also be useful for defeating GM's OnStar system and maybe even cellular phone detonated IEDs.

Construction Notes & Pictures

Jammer circuit board overview.

A 45 MHz clock oscillator with an impedance matching network on the output feeds the LO port on a Mini-Circuits ADE-1ASK mixer.  The ADE-1ASK mixer is only designed to operate up to 600 MHz, but it works fine for this particular use.

The IF output of the mixer feeds a Mini-Circuits VNA-25 MMIC amplifier to boost the output RF power slightly.  The VNA-25 amplifier doesn't need any external components, so it's perfect for this application.  The current draw is kinda high, though.

A 78L05 voltage regulator supplies the necessary voltage to the oscillator and VNA-25 from a standard nine volt battery.

Alternate view.

The jammer should be built on a small piece of double-sided FR-4 PC board with liberal use of ground vias.

Case overview.

It's built into an old Hammond die-cast aluminum box and the mini-UHF antenna connectors were from old Motorola bag-style cellular phones.

Attach the RF connector coaxial pigtails to the circuit board.

Completed internal view.

The nine volt battery is mounted against some pieces of art foam and a SPST power switch was added to the cover.

Completed case overview.

Folding cellular phone antennas with mini-UHF connectors are available on old Motorola cellular phones.  These antennas are nice and compact, which is perfect for this project.

"Mess with the bull, you get the horns."


Datasheets & Notes