Cell phone detector?
Is there a way to detect the presence of an active cell phone? The idea is to detect a switched-on phone where such a device is not permitted.
E
Yes, phones even in the receive mode put out transmitted signals to keep the node points aware of their existence in their area. This way when the phone goes to the next geographic zone that one knows to handle any calls.
Use the old military EW radar warning receiver method. Go antenna- wide band amplifier covering each band-detector-video analyzer.
The pulses out of the detector will be set by the phone protocol so you need to do some complex analysis which a uP can probable do. Pulse rep rate and width will probably be enough for each protocol on each band.
The hard part is the ones that are on all the time like spread code multiplexed. You can do a level detect as long as your system does not respond to out of band signals. I suspect that some simple band pass filters would help. Also having several such units at different places in your geographic area (meeting room, hospital, or whatever it is) will increase the probability of detection.
How long will you be waiting until you have detected a cell phone? If you simply want to walk through a couple of persons and to check who has a cell phone switched on (as in an airplane) you must have a short detection time.
I don't think that cell phones in idle state (receiving mode) do transmit so often. Isn't there a possibility to force the phone to send? (A protocol implementation). Or is there a chance to 'disturb' the frequency-band so the phone will immediately start sending?
Bye