Comment by ErroneousBosh

> and you were able to (somehow?) from the antennas perspective, see the "direction" the frequency was coming from..

You can kind of do that quite easily at low frequencies, by measuring the phase of signals coming in from a pair of aerials. If you put two aerials a quarter of a wavelength apart and switch between them very quickly at audio rate, then you'll get a tone when there's a difference in phase. If there's no tone the two signals are exactly in phase - the two aerials are exactly the same distance from the transmitter.

If you look on some police cars you'll see a group of four aerials about 15cm apart stuck to the roof which used to be used for "Lojack" style trackers.

There are a whole bunch of circuit diagrams floating around for doing this kind of thing, with the simplest being Ye Olde 555 timer and a couple of PIN diodes!