Apparently some people from called Fernau Aviation in Luton manufacture DVOR ground stations systems (as well as DME, TACAN, NDB and DF equivalents). They have a spec for their DVOR ground station system online at
http://www.fernau.com/library/items/2050_dvor_tech.pdf
The spec gives the impression that the RF side of things only generates amplitude modulation (AM):
- Reference Phase Modulation (AM) - 30Hz
- Variable Phase Modulation (AM), Sub-Carrier frequency 9960 Hz, frequency of modulation 30Hz
- Voice Modulation (AM), 300 to 3000Hz; and
- Identification Modulation Tone 1020 Hz
This seems to imply that the only other form of modulation would be the "space" modulation achieved by feeding the sub-carrier mod signals to the 48 antennas mentioned elsewhere...
Or maybe the spec is oversimplified..?
Keef: yes from receiver's point-of-view its all very simple!
Andy
A simple explanation from
avionics.com:
The VOR signal consists of a carrier frequency from 108.00 MHz to 117.95 MHz in 50 kHz steps. Modulation is a 30 Hz variable sine wave amplitude modulating the carrier. Simultaneously, a 9960 Hz subcarrier also modulates the RF carrier but the subcarrier is frequency modulated with 30 Hz. The phase difference between the two 30 Hz sine waves is the VOR bearing between the aircraft and VOR station. [...] A 1020 Hz amplitude modulated tone is [also] available for the Ident modulation.
So: 1) a simple AM reference signal, and 2) a ~10kHz subcarrier with FM modulated signal (whose phase relationship to the first signal varies according to radial position around the beacon).
I feel I owe
FFF a beer
Andy