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.
2-3
The sequential energizing of the sideband antennas and the 30 Hz amplitude modulation of the carrier are time
r
elated in such a way that the reference and the variable phase 30 Hz signals are in phase at zero degrees (0)
magnetic from the DVOR station. As the receiving point is moved clockwise around the station, the variable phase
signal (30 Hz FM) begins to lead the reference signal (30 Hz AM). For example, for the observer west of the
DVOR, the 30 Hz FM signal leads the 30 Hz AM signal by 270 degrees. The aircraft receiver determines the phase
difference between the two 30 Hz signals and thus it’s bearing in degrees (magnetic), relative to the station, as the
number of degrees by which the 30 Hz AM signal lags the 30 Hz FM signal.
2.2.1
DVOR Antenna Principles
The DVOR antenna system simulates a rotating arm with a transmitting antenna at each end, radiating the upper
sideband signal from one end and the lower sideband signal from the other end. This is achieved electronically by
using 48 antennas spaced equally around the perimeter of a circle 44 feet (13.4 meters) in diameter, with an antenna
in the center of the circle radiating a reference carrier.
Consider the effect of simulated antenna rotation on an airborne receiver. When the upper sideband source is
moving toward the aircraft, the Doppler effect causes the airborne receiver input frequency to become higher than
fc+9960 Hz, and for the lower sideband source, which is moving away, the frequency becomes less than fc±9960
Hz, fc being the carrier frequency. The frequency difference changes sinusoidally due to the simulated rotation.
The difference is at a maximum when the line joining the two radiating antennas is perpendicular to the radial to the
aircraft. The difference is equal to zero when the two sideband sources align with the radial to the aircraft since, at
that moment, the distance between each sideband source and the receiver does not vary.
The moment of zero frequency deviation is different for different positions of the aircraft around the station.
Therefore, the recovered 30 Hz FM signal will have a different phase for each of these different positions. For the
receiver North of the DVOR station, the 30 Hz FM signal must be in phase with the 30 Hz AM signal; both signals
passing through their positive zero crossings at the same time. To achieve this, the following has to be observed: At
the moment that the 30 Hz amplitude modulation of the carrier is passing through its positive zero crossing, the
simulated rotating antennas shall align with antenna number 1 (at North) and antenna number 25 (at South), with the
North antenna radiating the peak of the lower sideband signal and the South antenna radiating the peak of the upper
sideband signal. The lower sideband frequency will be decreasing; the upper increasing. The subcarrier frequency
will be increasing from exactly 9960 Hz up and the 30 Hz FM signal will be passing through its positive zero
crossing.
2.3
DVOR TRANSMITTER THEORY OF OPERATION
The following paragraphs provide a technical description of the Model 1150A DVOR, its individual components
and accessories. Refer to Figure 2-2 for simplified block diagram of the DVOR Transmitter System and Figure 2-3
for a detailed block diagram of the DVOR system.
2.3.1
Simplified System Block Diagram
Refer to Figure 2-2. The transmitter (main and standby) consists of a frequency synthesizer assembly, CSB power
amplifier assembly, directional coupler, audio generator CCA, and two sideband generators,
The frequency synthesizer assembly produces the three interrelated RF signals used by the DVOR. The on- channel
carrier RF signal drives the CSB power amplifier assembly. The upper and lower sideband RF signals drive the two
sideband generator assemblies.
The CSB power amplifier assembly amplifies and modulates the carrier RF signal to the operational output level.
The CSB power amplifier also provides a sample portion of the RF energy to be used as an error correction that is
sent back (feedback) to the frequency synthesizer assembly.
The bi-directional coupler obtains a sample of the forward and reflected RF carrier power. The sampled forward
and reflected power is directed to the RF monitor assembly where the signal is used in the detection and analysis
process circuitry.