The Dvor (Doppler Very High Frequency Omnidirectional Range) is a radio navigation aid developed for short and medium-range aircraft guidance, operating within the 108-118 MHz VHF frequency range with a transmission range of 300 km. It provides pilots with critical positioning information such as azimuth, bearing, and 'from/to' indications by utilizing a phase angle difference between two 30 Hz signals. The system complies with ICAO standards, can operate as single or dual equipment, and can be integrated with other navigation systems like DME and TACAN.

1. DVOR
Doppler
Very High Frequency Omnidirectional Range
Afghanistan Civil Aviation
Institute
Ahmad Sajjad Safi
CNS Instructor
Reference:
DVOR 432 Technical Manual

2. Introduction to DVOR
 The DVOR is a radio navigation aid recommended by the ICAO and
introduced internationally for short and medium range aircraft guidance.
 The DVOR radio navigation equipment is a further development of the
conventional VOR.
• Todays airway network is marked by a number of DVOR ground beacons
operating in the 108...118 MHz VHF frequency range and having a
transmission range of 300 km.

3. DVOR Airway Route
Aeronautical Map

4. DVOR Propagated Information
 Using the VOR receiver installed in the aircraft the pilot is able to obtain
the following information from a DVOR radio navigation installation:
- The azimuth indication of the aircraft’s position relative to the ground
beacon, i.e. the angle between magnetic North and the direction ground
beacon to aircraft.
-The bearing which indicates whether the aircraft is flying to the left or right
of the preselected course (position line) or whether it is exactly on it.
-The "from/to" indication which shows whether the aircraft is flying toward
the DVOR beacon or away from it.

5. DVOR Propagated Information
 To evaluate the indications only a map is required, and the knowledge of
the DVOR positions and a DVOR frequency chart.
 The aircraft position is marked by the intersection of two position lines in
the cockpit DVOR indicator.

6. DVOR Propagated Information
 When flying ±30° vertical elevation over a DVOR a loss of signal is experienced
as the aircraft passes through the “CONE OF SILENCE.

7. Operational use of DVOR
 DVOR located at or near an airport not only provides bearing information
for an approach to that airport, but also provides en-route bearing
information to aircraft overflying or using the airway on which the DVOR is
serving. A number of DVOR’s are therefore placed along the airways to
provide continuous bearing information.
 En-route navigation with DVOR, principle

8. Principles of the DVOR
 The principle on which the DVOR operates is based on the measurement
of the phase angle difference of two 30 Hz signals radiated by the station
at the same time.
 One signal (reference signal) is radiated with the same phase in all
directions. For the second 30 Hz signal (variable signal), the phase of signal
is variable.
 The electric phase angle measured in the airborne receiver to identify the
azimuth angle.
 This bearing (azimuth) angle also known as RADIALS will be displayed on
DVOR indicator inside the cockpit.

9. Principles of the DVOR
 Azimuth as a function
of the phase angle.

10. Principles of the DVOR
 Reference Signal : the 30 Hz modulation which amplitude−modulates (AM) the
VHF carrier now acts as the reference signal. The modulated carrier signal is
transmitted Omni directionally by a center antenna. It is amplitude−modulated
with the voice (300...3000 Hz) and the identity Morse code in addition to the 30
Hz reference signal.
 Variable Signal: the 30 Hz modulation which frequency−modulated (FM) 30 Hz
modulation (variable signal) is contained in the 9960 Hz subcarrier. The 9960 Hz
subcarrier signal is transmitted directionally by a sideband radiator antenna,
which can be considered to be rotating along a circular path. The radiated
sideband frequency is offset by +9960 Hz or −9960 Hz with respect to the carrier
frequency.
 ICAO stipulated ±480 Hz signal in order to obtain the frequency deviation.

11. Principles of the DVOR
 Frequency spectrum of the DVOR radio beacon:

12. General Information of the DVOR
The main features of DVOR 432 is as follows:
 Compliance with ICAO standards.
 Available as single or dual equipment with power up to 50 W or 100 W.
 Microprocessor controlled transmitter and monitoring system.
 Modular design, extensive common use of subassemblies within the Navaids.
 Local LCD display and control panel for system status indication, basic controls
and measurement of data.
 Standard PC used as local or remote interface (via RMMC) between the system
and the operator.

13. Operational use of DVOR
 The DVOR system can be combined with a DME, TACAN and VORTAC.
 These symbols denotes beacon installation on an aeronautical chart.

14. Operational use of DVOR
• The DVOR system can be combined with a to form a DVOR/DME station. Then
an aircraft can determine its position by referring to the location of a single
DVOR/DME station.
DME Antenna

15. Principles of the DVOR