DVOR
DVOR- is a navigational aid equipment designed to provide bearing information to aircraft.VOR Systems composed of a transmitting station on the ground and receiving station on the aircraft.
VOR Stations:
a.En-route -112MHz-118Mhz
b.Terminal -108MHz-112MHz
The DVOR radiates a radio frequency carrier with which are associated two separate 30 Hz modulations.
One of these modulations is such that its phase is independent of the azimuth of the point of
observation (reference phase). The other modulation (variable phase) is such that its phase at the
point of observation differs from that of the reference phase by an angle equal to the bearing of the
point of observation with respect to the DVOR. Compared to a CVOR station for the DVOR system
both 30 Hz modulations are reversed. The conventional VOR is more sensitive for multipath reflections
from fixed object, near and distant, such as trees, power lines, buildings and mountains which
rise the bearing errors. The improved radio navigation beacon DVOR relies on the Doppler change
in frequency which would result if a radiation antenna is moved around a large diameter circle. If the
antenna is rotated 30 times a second, the signal at a distant observation point will be frequency modulated
at a 30 Hz rate. The modulation index is determined by the diameter of the circle.
The DVOR radiates a radio frequency carrier with which are associated two separate 30 Hz modulations.
One of these modulations is such that its phase is independent of the azimuth of the point of
observation (reference phase). The other modulation (variable phase) is such that its phase at the
point of observation differs from that of the reference phase by an angle equal to the bearing of the
point of observation with respect to the DVOR. Compared to a CVOR station for the DVOR system
both 30 Hz modulations are reversed. The conventional VOR is more sensitive for multipath reflections
from fixed object, near and distant, such as trees, power lines, buildings and mountains which
rise the bearing errors. The improved radio navigation beacon DVOR relies on the Doppler change
in frequency which would result if a radiation antenna is moved around a large diameter circle. If the
antenna is rotated 30 times a second, the signal at a distant observation point will be frequency modulated
at a 30 Hz rate. The modulation index is determined by the diameter of the circle.
Azimuth angle between aircraft and ground station
The effect of a rotating antenna is simulated by using a ring of antennas and switching the RF signal to each in turn. Provided sufficient antennas are used and the pulse RF energy is suitable shaped, the simulation is good. The shape of the modulation envelope is called the ’blending function’. The azimuth−dependent information is contained in the phase of the frequency modulation.The reference phase of the 30 Hz amplitude modulated carrier signal is radiated from a single antenna at the center of the ring. The aperture of the Doppler VOR antenna is much more greater than in conventional equipments. By virtue of the resulting ’space diversity’, effects due to reflections are greatly reduced. The bearing information is inherently determined by the geometry of the antenna array and since the Doppler VOR array is large it can be made very stable and accurate. The DVOR 432 is a Double Sideband DVOR system (DSB DVOR) and is full compatible with all existing airborne VOR receivers. In a DSB DVOR system signals 9960 Hz above and below carrier frequency (Upper Sideband →USB / Lower Sideband → LSB) are radiated simultaneously from 48 sideband antennas diametrically opposed to the ring. Both sidebands are commutated at 30 Hz in the same direction.
