I want to make a robot that can track the direction of the transmitter that is controlling it, for example to aim a camera at the transmitter. The robot vehicle will be controlled by a 2.4ghz NRF24L01+ link from within about 40 meters away.
I found this page which uses antenna switching to accomplish something quite similar: http://www.robowarner.com/robot/rdfbotarduino However, as he points out "This project requires a transmitter that outputs a clean, unmodulated waveform."
Thankfully, I can mostly grasp the concept of how that particular example works, but what I don't understand is how this same type of RDF was used in wartime to locate signal sources that not only were not outputting clean waveforms, they were doing their best to remain hidden.
So there must be another variant on this method that does not rely on the source signal being of a certain type, right? It would be great if I could just do antenna switching with my receiving NRF24L01+ and do the same kind of phase comparison, but I guess that ain't gonna work (would it also screw up the communication?).
Any ideas about a good way to proceed? I suppose I could transmit a second, clean waveform, from the transmitter as well, but it would be nice if there was some way to avoid doing that.
(Bonus marks if you can tell me why that guy is switching the antennas four times before taking a reading... is once not enough?)