Case 1: Radio location of a continuous RF pure tone.

Consider a stationary RF beacon, S1, single point source of an omnidirectional radio signal, for now, a pure tone at a single frequency F1.

Consider a stationary radio receiver, R1 located at some significant distance away tuned to the frequency F1.

Consider a second stationary receiver, R2, at a significant distance away from the beacon and the other receiver R1, also itself tuned to F1.

Because the signal at F1 is a pure tone, it is impossible to locate S1 because there is no apparent difference in the Signal S1, except for phase difference.

Phase can vary from 0 to 2 pi radians, or 0 to 360 degrees. This means that there can be a phase error less than 1 cycle distinguishing the two signals.

If the phase error = 1 cycle, that would look like no phase error at all! If the phase error > 1 cycle then it looks like the original signal with a phase error between 0 and one cycle.

So an unmodulated pure tone cannot be located except by its phase and that limits what can be known. I wonder if this has quantuum mechanical interpretations?

A 10 Mhz pure tone with no modulation has a wavelength of 100/10 = 30 meters. So the absolute distance to the pure tone cannot be known unless S1 is closer to R1 than 30 meters.

The limitation of knowing is such that given phase information only on a pure sinusoidal tone that the following could be true of the distance between S1 and R1.

distance
  0 < d <= 30 meters OR
30 < d <= 60 meters OR
60 < d <= 90 meters

and so forth. The only information detectable is phase information, and that information only tells you that the object  is integral number of wavelenths + a partial phase controlled wavelength away.