Numeric Measurement Modes
R&S
®
EVSG1000
102
User Manual 1178.6227.02 ─ 06
The VOR signal contains three AM modulated components that must be separated in a
first step:
●
Rotational signal (30
Hz)
●
Identification/voice part (300
Hz to 4
kHz)
●
FM modulated carrier (9960
Hz ± 700
Hz)
To obtain the AM depth, a lowpass filter must calculate the mean carrier power, while
suppressing all other signal components. The mean carrier power is then used to nor-
malize the instantaneous magnitude of the I/Q signal. The result is the AM modulation
depth signal vs. time. The three AM components are separated using bandpass filters
covering the individual frequency ranges.
A Morse decoder detects and decodes the ON and OFF periods in the identifier signal.
The separated FM modulated carrier is passed through an FM demodulator. The FM
carrier frequency (nominal 9960
Hz) is calculated as the average output value of the
FM demodulator. To obtain the 30
Hz reference signal, the FM demodulator output is
filtered by the same narrow 30
Hz bandpass as the 30
Hz AM rotational component.
FM deviation is calculated using the estimated magnitude of the 30
Hz reference sig-
nal.
The azimuth is calculated as the phase difference of the 30
Hz reference signal and
the 30
Hz rotational signal.
VOR distortion
In the VOR software demodulator two kinds of signals are analyzed regarding distor-
tions:
●
AM Distortion: The AM modulation depth vs time signal is processed by an FFT,
with a user-defined resolution bandwidth. The trace is displayed in the Modulation
Spectrum display. The K2, K3 and THD results of the AM components are calcula-
ted based on the FFT trace and the estimated modulation frequencies.
●
FM Distortion: The FM modulation depth vs time signal is processed by an FFT,
using a resolution bandwidth automatically set by the application. You cannot view
the resulting trace. The K2, K3 and THD results of the FM components are calcula-
ted based on the FFT trace and the estimated modulation frequencies.
AM Modulation Depth
To obtain the AM depth, a lowpass filter must calculate the mean carrier power, while
suppressing all other signal components. The mean carrier power is then used to nor-
malize the instantaneous magnitude of the I/Q signal. The result is the AM modulation
depth signal versus time. It is then used to calculate the following AM modulation
depths:
●
Depth
9960
: AM modulation depth of the FM carrier, typically at 9960
Hz
●
Depth
AM30
: AM modulation depth of the 30
Hz rotational signal
●
Depth
ID
: AM modulation depth of the identification/voice signal
VOR Mode (Option R&S
EVSG-K2)