I´ve had trouble understanding exactly how the signal encoding would work to transmit both the reference and the variable-phase signal...
I´ve finally found an excellent source here: http://wwwtvs.et.tudelft.nl/P&N/education/et4-022/et4-022.htm
The section that deals with VOR/DME
/ILS is "Aviation - en route"
with the long explanation here: http://wwwtvs.et.tudelft.nl/P&N/education/et4-022/notes/h7.pdf
The respective overhead sheets provide a good illustrated summary as well (can´t link to them due to the freakin´ a.net HTML conversion.
Apparently, both signals are transmitted on the same carrier, with the variable-phase signal being amplitude-modulated on the main carrier at 30 Hz, and the reference signal FM
-encoded with a 9960Hz sub-carrier on the same signal. (In between, there´s still space for audio transmission of the beacon´s ID
The documents also explain the Doppler VOR system (with reversed signal encoding) and ILS, among other things.