If you amend that to "A GPS with RTK" - then that would work very precisely, if the item was outdoors.
RTK gives accuracy in the centimetre range.
At around 400 MHz, a small pseudo "Doppler direction finder" is very practical.
There are numerous designs around, using two or four antennas.
The principal is that you use simple logic or an MCU plus diode switches to cycle through the antennas at audio frequency, a few hundred hertz.
The changing distance between "the antenna" (in use at each instant) and the target gives an audio tone through an FM receiver. The phase of that audio tone gives the direction to the transmitter.
Example design here:
Doppler shift: First, let’s get to understand what Doppler shift is. Everybody knows of the pitch change of a fast moving object, like a passing car. The motor or horn sound of a car at const…
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