The n900 has an FM-emitter and an FM-receiver.

FM-waves are electro-magnetic waves and they propagate inside the geomagnetic field. The geomagnetic field influences electromagnetic waves.


This allows us to measure some characteristics about the geomagnetic field.

We can emit an electromagnetic wave on one frequence and we can measure the dispersion of the same wave arround the same frequence on the receiver.

This gives us a two dimensional field of values (For each frequence of the FM-emitter we get the range of dispersion on the side of the receiver.)

In fact we have a three dimensional field. Because we can emit audiosignals in the whole audible range over one frequence of the emitter.


Now we can hope that this values are characteristic for the direction inside the geomagnetic field.

Yes many FM-frequencies are occupied by public stations, others aren't.
In a very short distance the influence of public stations can be neglected (That's why you can use it inside your car.)
You can even filter the influence of public stations: You emit a characteristical audio signal. You will see the effect of strange signals.

I think that you can use the emitter and the receiver at they same time: They are on completely different chips with different technology. I don't see any diffculty to using both at the same time.

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.

The transmitter driver can scan for signal strength at frequencies (though Nokia is not using this feature in their software). Could this help already?