VOR evolutionary system improvements in the United States

This paper discusses the techniques and system performance for several classes of VHF Omnidirectional Range (VOR). Single- and double-sideband Doppler VOR are compared with the alternating-sideband VORDAC proposed to EUROCONTROL. Results of the tests conducted on all three techniques are discussed along with the reasons why the U. S. favors a “full-time” double-sideband Doppler VOR. Results of recent tests of the Precision VOR, using the two-speed multilobe pattern combined with simultaneous operation of the Doppler VOR, are presented.