Do you intend to sell this device? If so, prevention is guaranteed by the fact that you'll never get FCC approval for it.
If you're approaching it from a security standpoint, imagining a target which is relying on NFC restrictions of 1 meter vs. several meters to protect valuable data, you could create such a device. It would be expensive, and thoroughly illegal. If your target has data that's worth more than the cost to build such a device, then they're probably not going to keep it in a format where it could be accessed via NFC.
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 — 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 ±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.
Best Answer
You're misinterpreting that sentence.
There's no new concept introduced in
It's simply that if your signal quickly loses power over distance, someone else can use that same part of the spectrum e.g. for their own calls.
Given technical users per cell limitations, the operator of the cellular network needs fewer spectrum licenses when their signals don't reach far.