Radio direction finding - dependence on source signal type
I don't know which war you might be thinking of, but in general that kind of direction-finding involves techniques other than TDOA.

The TDOA technique works with the cheap FM walkie-talkies because the antenna switching causes a phase shift in the received signal, which can be decoded by the FM detector. (The two are closely related &mdash; phase is simply the integral of frequency.)

The technique requires a "clean" (unmodulated) carrier, because any modulation introduced in the transmitter would also appear at the speaker output of the receiver, confusing the algorithm that's looking for changes that are synchronous with the antenna switching.

Based on a preliminary look at the nRF24L01+ datasheet, it doesn't appear that the same antenna-switching trick will work with this chip. It does all of the protocol processing internally, and simply doesn't provide the low-level access to the signal that you'd need for the TDOA technique. Yes, if anything, you'll simply degrade the communications.


  Bonus marks if you can tell me why that guy is switching the antennas four times before taking a reading... is once not enough?


The problem is that everything is AC coupled, and you need multiple cycles in order to allow the transient effects to die out. The antenna switching is driven by a capacitor, which converts the 0-to-5V control signal from the micro into a &plusmn;2.5V signal to drive the PIN diodes. Also, the audio path through the receiver is AC-coupled, which means that the output associated static changes in carrier phase dies out over time. For both of these reasons, you need multiple cycles of switching in order to get an unambiguous result.