How do navaids work?
I was wondering if some kind soul can point me in the direction of some technical information about how common navaids work?
For instance, I am aware that a localizer emits 90Hz and 150Hz tones on either side of the centre-line, which presumably modulate the carrier. I would imagine that the receiver in the cockpit demodulates the signal and uses the amount of the measured tone at the two frequencies to move the needle.
I'm specifically interested in localizers, VORs and DME. I don't have any particular use for the info other than being curious from an engineering standpoint as to how both the transmitter and receiver portions work.
Many thanks!