Basically, you need a receiver tuned to the general frequency and a directional antenna.
Search for "amateur radio foxhunt" or "rf sniffer". Amateur radio operators do this for fun; it is called a "foxhunt", where a transmitter is hidden and participants try to find it in the shortest time.
Ooooh- my my my- what fun!
It is to the guys involved. It is also used to teach people to build the receivers and directional antennas. The prizes given to the winner helps, too. ;-) Go to a large hamfest sometime, and you'll see guys wandering around looking for the hidden transmitter, with hundreds of other radios on the same band in use while they search. A lot of time and effort go into the design and building of the radios and the antennas.
A "good" cellphone jammer will only transmit when a phone is transmitting. And a phone will not transmit very long if the jammer is on...
Thomas
What are the prizes like?
How about staking down two receivers, with GPS, dual beam nulling on each- report AOA to central processor for xmit location calculation- fire mortar at xmit and destroy it.
I have seen a new ham rig as the first place prize, at least $250 value.
Why destroy it? It is intended to test your skills in locating the source of a weak signal, and to see how fast you can do it. They run several rounds, and the shortest time to locate it, wins. This hobby has been around since the days of miniature tubes, and "B" battery packs, or maybe even longer.
Now we are starting to get complex. Wide band receivers which can identify cell-phones from other legitimate users on adjacent frequencies, determine which frequency the cell-phone is currently on and transmit a signal which will overpower the cell-phone transmitter. And, if it is going to work, be able to monitor the cell-phone while jamming so that it knows when to stop the jamming signal.
We are starting to get into the realm of military ECM.
Why not jam the phone's reception of the control channels? So much simpler, easier, lower power requirement etc. etc.
Dave
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