Numeric Measurement Modes
R&S
®
EVSG1000
98
User Manual 1178.6227.02 ─ 06
4.3.1
VOR Basics
Some background knowledge on basic terms and principles used in VOR measure-
ments is provided here for a better understanding of the required configuration set-
tings.
4.3.1.1
VHF Omni Directional Radio Range (VOR)
Very high frequency (VHF) omnidirectional radio range (VOR) is a radio navigation sys-
tem for short and medium distance navigation. The VOR radio navigation aid supplies
the aircraft with directional information, angle information relative to the magnetic north
from the site of the beacon. Thus, it helps aircraft to determine their position and stay
on course. The range covered by a VOR station is ideally a circle around the VOR sta-
tion with a radius depending on the flight altitude.
A VOR system consists of a ground transmission station and a VOR receiver on board
the aircraft.
Ground transmitter
The transmitter stations operate at VHF frequencies of 108
MHz to 118
MHz, with the
code identification (COM/ID) transmitting on a modulation tone of 1.020
kHz. It emits
two types of signals:
●
An omnidirectional reference signal (REF) that can consist of two parts:
–
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
(CVOR) transmits with a rotating antenna. From the rotation, a sine wave AM 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.
Instead of using a rotating antenna, DVOR stations (Doppler) divide the circumference
of the antenna into 48 or 50 segments, covering each segment by its own antenna.
Each antenna transmits the unmodulated subcarrier from one antenna to the next, so
that the signal completes the round trip 30 times per second.
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.
VOR Mode (Option R&S
EVSG-K2)
