Tracking mobile phones

[Styx]

was a bit bored and came across this. I havn't examined it in detail but thought some1 might be interested in it

http://www.voltsamps.com/pages/projects/cell/

 

[Exo]

Am i missing something here or is all he's using just 4 RF diodes to detect the signal ?

 

[pike]

I'm questioning the same thing here. How exactl would a basic stamp be able to detect a 300Mhz + signal when the proceesor doesn't work that fast??

 

[Nigel Goodwin]

I'm questioning the same thing here. How exactl would a basic stamp be able to detect a 300Mhz + signal when the proceesor doesn't work that fast??

I thought cell phones were about 900MHz? - but in any case, the bridge rectifer is to convert the signal to a DC voltage - there will be plenty of stray capacitance to smooth a 900MHz signal.

However, it's obviously not intended as a practical unit, simply as a crude demonstration that a cell phone transmits periodically all on it's own. Notice how close the phone is in the video clip, that's probably as far away as it works.

Certainly you could track a transmitter in this way, it's called DF'ing (Direction Finding) and has been used ever since radio first started. But for a cellphone it's an incredibly crude technique, you would need to be fairly close, and there only be one working cellphone in range. And, of course, you need two readings from different locations.