Doppler VOR is actually a beautiful piece of physics.
The beacon consists of a ring of antennae and a central one. They are capacitance loaded dipoles on a ground plane reflector to give an optimum radiation pattern.
The central antenna radiates a signal at the frequency of the VOR with a 30 Hz amplitude modulated signal, the beacon ident and any colocated ATIS etc. This forms the reference phase.
The ring of antennae are commutated in such a way that opposing antennae radiate a signal modulated at 9660 Hz, and they switch sequentially so that the pairs rotate around the beacon at 30 rpm.
The ring is 13.6m in diameter, and if you do the math, a distant observer will observe the signals from both antennae, with one approaching and one receding with such velocity that each signal is doppler shifted. The summation at the receiver is that of a frequency modulated 30 Hz variable signal.
The receiver calculates the phase difference between the FM variable and the AM reference 30 Hz signals to extract the bearing information.
The advantage over '
conventional' VOR is that siting errors are very much reduced eg scalping of radials and false bearings. This is because the '
aperture' is much larger for a DVOR than the smaller antenna on a CVOR and so spatial resolution is enhanced.
Think about the objective lens on a big telescope vs small telescope.
As Brian Cox would say - amaaaazing. What a shame we just use Tom Toms these days
