cell phone jammer - cheap and easy

Lets ignore the legal and ethical questions for a moment, and acknowledge that sometimes it would be nice to have a device to silence cellphones and their users in our vicinity.

You can buy ready-made units to do this on the internet, but they are very expensive. There are also vague plans out there to build your own (ie wave bubble) but they are way overcomplicated, and here's why.

The plans essentially have you construct the RF filter, amplifier and signal generator yourself. This requires obtaining obscure expensive components, performing surgically difficult SMD soldering, and using advanced test equipment to test and align the RF stages.

Why bother with this when most people already have one or more complete RF amp, antenna, and signal generator packages lying in their junk drawer: an old obsolete cell fone!

Simply program a small microntroller to generate a random-noise base signal and possibly the serial control strings for the PLL chip and wire it into the cellfone's circuit. Ok, that part might be a little tricky, but a little collaboration with the online hacker community could easily produce diagrams for a handful of the more popular phones showing which wires to solder into to inject your rogue signal and activate the RF amp section etc... But all the hard work of creating the RF signal generator and amp and wave shaping circuits and antenna would already be done for you!

So worst case you would have an old cellfone with a small circuit board sandwiched to it externally which would have a PIC or other microntroller on it.

Or even better, invest some time into deciphering how to download a new firmware program into the phone's main CPU. If you can do that, it would be simple enough to write a small program to do nothing more than send random noise, at full power, on the correct frequency.

An effective jammer does not necessarily need to be outputting a significantly higher power level than the devices it wishes to jam. most Cellfones use CDMA technology which means they are all essentially broadcasting on the same frequency, but they are all synchronized with the base station and transmit different "codes" within that frequency to allow the base station to decipher them individually. However, a single rogue phone on the CDMA frequency that is constantly blasting out garbage noise instead of carefully synched CDMA codes will drown out its immediate neighbors...