User's Manual

Model 1150A DVOR
Rev. - November, 2008
This document contains proprietary information and such information may not be disclosed
to others for any purposes without written permission from SELEX Sistemi Integrati Inc.
2-1
2 T
ECHNICAL DESCRIPTION
2.1
INTRODUCTION
The Model 1150A DVOR system is a dual transmitter system, with dual monitoring facilities. It is designed for
terminal and en route navaid operation. The VOR is identified by a specifically assigned two to four letter Morse
code identity and may also include voice identification. In addition automatic terminal information service (ATIS)
information may be modulated onto the VOR signal with a standard input connection. The DVOR can be collocated
with DME to provide distance information in addition to bearing data.
The DVOR concept is based on the 360° radials which originate from a transmitting station and on the airborne
equipment which resolves the particular radial data from the station. The resolved radial, called line-of-position
(LOP) is the displacement angle between magnetic north and the aircraft, as measured from the DVOR antenna.
Therefore, regardless of its heading, an aircraft which is on the 0° radial is north of the DVOR station. The
magnetic course to the station is the reciprocal of the radial. In addition, to/from orientation data, relative to the
DVOR station, is also resolved by the airborne equipment.
2.2
OPERATING PRINCIPLES
Operation of the DVOR is based on the phase difference between two 30 Hz signals modulated on the carrier, called
the reference phase and the variable phase.
The reference phase signal is obtained by amplitude modulating the carrier with a 30 Hz sine wave signal. This
amplitude modulated (AM) signal is radiated omni-directionally in the horizontal plane by the central, carrier
antenna. The radiation pattern is a circle, and produces in the aircraft receiver a 30 Hz signal with a phase
independent of azimuth.
NOTE
DVOR system requires separately radiated upper and lower sideband frequencies which are
displaced ±9960 Hz from the carrier frequency. The Model 1150A DVOR has synthesizer
controlled frequencies which are assigned as follows: carrier (on-channel) station frequency,
carrier frequency plus 9960 Hz, carrier frequency minus 9960 Hz.
The variable phase signal is obtained from the 9960 Hz frequency modulated subcarrier which amplitude modulates
the carrier. This amplitude modulation of the carrier is often referred to as the space modulation, since it is obtained
by adding in space the omni-directionally radiated carrier and the separately radiated upper and lower sideband
signals emanating from the ring of sideband antennas. The upper and lower sideband signals are displaced, on
average, 9960 Hz above and below the carrier respectively and, when added in correct phase to the carrier, will
produce a resultant signal which is amplitude modulated at 9960 Hz.
The subcarrier is frequency modulated at a 30 Hz rate. The sideband signals are sequentially distributed to and
radiated from the 48 sideband antennas in such a way as to simulate two diametrically opposed antennas, rotating
counterclockwise about the circumference of the sideband antenna ring at 30 revolutions per second, with one
antenna radiating the upper sideband signal and the other the lower sideband signal. Since the effective length of the
path of travel between the rotating sideband sources and the distant point of reception varies at a 30 Hz rate, the
observed frequency of the sideband signals varies also at a 30 Hz rate (i.e., the sidebands) and therefore, the
subcarrier is frequency modulated at 30 Hz.
The amount of frequency deviation is proportional to the diameter of the sideband antenna ring expressed in
wavelengths at the operating frequency. Setting the diameter to 44.0 feet (13.4 meters) produces peak frequency
deviation of 480 Hz at a frequency of 113.85 MHz, 454 Hz at 108 MHz and 497 Hz at 118 MHz. Figure 2-1 depicts
a typical RF spectrum of a DVOR with an operating frequency of f
c
. The corresponding deviation ratio varies
therefore from 15.13 at 108 MHz to 16.57 at 118 MHz.