Wonder though what can be obtained, an N900 metal detector ... hmm does have a nice ring to it.

So breaking it down to components the following need to be done.

* Signal Emission (Frequency specificity is important)

* Signal Acquisition (Frequency selectivity is important)

* Signal Filtering & Amplification

* ADC

* Signal Processing

* Signal / Display Output

Also I also don't think the N900 can simultaneously measure and transmit. But it can measure diffraction, scattering, reflection, and refraction. Also propagation delay can be measured as well. The placement of both Transmitter and Reciever play a crucial part, and the type of Antenna is also crucial.