Numeric Measurement Modes
R&S
®
EVSF1000
67
User Manual 1178.6410.02 ─ 05
–
30
Hz frequency modulated (FM) sine wave on subcarrier 9.96
kHz from ampli-
tude modulation (AM) carrier
–
1020
Hz AM modulated sine wave Morse code
●
A directional positioning signal, variable (VAR): 30
Hz AM modulated sine waves
with variable phase shift
VOR receiver
The VOR receiver obtains the directional information by measuring the phase differ-
ence of two 30
Hz signals transmitted by the beacon. A conventional VOR station
transmits with a rotating antenna. From the rotation, a sine wave AM modulated signal
arises in the receiver, whose phase position depends on the present angle of rotation.
The rotation frequency of the antenna sets the modulation frequency at 30
Hz.
To determine the radial, the phase difference to a reference phase must be measured.
This reference phase must be independent of the rotation of the antenna. Thus, it is
modulated with a frequency deviation of 480
Hz in FM onto a secondary carrier with
9.96
kHz. It is then emitted over a separate antenna with a round characteristic.
Figure 6-12: Basics of the VOR phase angles (
Φ
) depending on the azimuth angle (
Θ
)
The frequency modulated secondary carrier for the reference phase is itself again
modulated in AM on the RF carrier of the VOR station. In addition to the signals neces-
sary for navigation, a Morse code with 1020
Hz can be transmitted on the VOR carrier.
Also, speech in the usual AF from 300
Hz to 3.3
kHz can be transmitted. Often the
voice channel of a VOR station is used for the transmission of ATIS (Automatic Termi-
nal Information Service) messages. The Morse code can be used to identify the VOR
station, similar to the
"Morse code identification signal"
on page 36 in the ILS signal.
The spectrum of a VOR signal is therefore composed of the carrier and three modula-
ted components.
VOR Mode (Option R&S
EVSG-K2)
