VOR Signals

[Port Strobe]

I'm having trouble understanding quite what is going on to generate the signals transmitted by the conventional VOR before Doppler VORs came to exist. I understand there are the reference phase and the variable phase signals. The reference phase signal is carried on a 9960Hz subcarrier which is frequency modulated at 30Hz with a frequency deviation of 480Hz. This signal is transmitted omnidirectionally such that at a given instant in time the phase of the signal is that same in all directions.

Now comes the tough bit, the variable phase signal. This is amplitude modulated at 30Hz but my understanding of how this is achieved is not great. I've read a couple of explainations but something isn't quite making sense with it. Some refer to rotation of the variable phase signal to achieve amplitude modulation but did the antennae actually rotate? If someone could please explain how this is actually achieved please I'd be very grateful. The points I'm having most trouble with are the mechanism for amplitude modulation of this signal and how all this relates to the phase of the received signal which is after all how the a/c determines its position. If you could highlight these points please I'm sure the penny will drop.

I have searched the forums and read some replies to questions along the same line but its not sinking in, sorry. For any mods viewing this I've also posted this in the Ground Studies forum to try and maximise my chance of an answer, I don't discriminate who gives me the correct answer :ok:

Thanks very much indeed

[Port Strobe]

Thanks for the links ASFKAP, I'll see what I can find on those sites as well.

[winglit]

Yes, you are right. On the earlier VOR beacons the aerial actually rotates.

[Port Strobe]

Thanks for the replies guys. Between your answers and the ground studies forum I'm pretty much sorted with respect to its operation. Thanks again for your time.