Instrumentation & Measurement Magazine 24-4 - 108

Table 1 - The specifications of
measurement instruments
◗ Very-high-frequency Communication System (VHFCS)
(118∼136.975 MHz): 119 MHz, 126.48 MHz, 128 MHz, and
135 MHz.
Instruments
Name
Specifications
Model
Name
Frequency
range
EMI receiver ESCI-3
Resolution
ratio
Test
specification
Bi-conical
antenna
Log-periodic
antenna
Radar speed
measuring
instrument
HK116
HL223
Bushnell
101921
Frequency
range
Frequency
range
Velocity range
Measurement
accuracy
Data
9 kHz ∼ 3 GHz
0.1 Hz
+30 ∼ -147 dBm
20 ∼ 300 MHz
300 MHz ∼ 2 GHz
10-321 km/h
1.0 km/h
Name
OBS
Table 2 - Polarization modes of antennas
Antenna
VHFCS
GBS
Bi-conical
Bi-conical
Log-periodic
◗ Glide Beacon Station (GBS) (328.6∼335.4 MHz): 329.3
MHz, 330.5 MHz, and 332 MHz.
The E values obtained by PK detection are fluctuant. Therefore,
the maximum value is used to analyze the most serious
radiation. Because the electric field intensity will decrease
with the distance, the measurement results cannot reflect the
real intensity of EMI from the source. For contrast, the results
are converted to the values at the equivalent 10 m distance by:
E En D
D
10
10  20log ( / 10)
(10)
where E10 and ED are E at the distance of 10 m and D m from the
arc, respectively; and n is the coefficient related to frequency,
as shown in Table 3.
The values of D and ED
can be obtained by measurement
(the abnormal data are excluded by the Grubbs method [27]
and replaced by retesting to reduce the test error), and E10
can
be calculated by (10). Then, we can fit the linear relationship
between the frequency (f) and E10
:
Polarization
Horizontal
Perpendicular
Horizontal
According to the standards [4] and [5], the polarization
modes of antennas are listed in Table 2. The parameters of the
EMI receivers are set by the standard [25] and the EM environment
on site, as shown in Fig. 5 (a screenshot of the EMI
receiver for one of our measurement results), and the operation
method of the ESCI-3 EMI receiver is shown in [26]. The
standards specify that the emission from the railway system
to the outside world should be analyzed and evaluated by the
data using the peak (PK) detection.
In this paper, the following typical frequency points of the
airport navigation stations are selected:
◗ Omnidirectional Beacon Station (OBS) (108∼117.975
MHz): 108 MHz, 109.7 MHz, 110 MHz, and 115 MHz.
N
E a fb log ( )
10
10

(11)
where a is the regression coefficient, and b is the intercept. They
are calculated by:

   
 

10 ii
10
a


N
[log ( )]2
i1
  log ( )
bE a
10
10 f
where i and N are the ordinal and total number of the samples.
According to the number of frequency points measured,
N is 11.
The curves of f and E10
at different speeds can be obtained,
and the relevant parameters are listed in Table 4.
Assessment Process of EMI
EMI Limit for Navigation Signals
The track of the train we
tested is almost perpendicular
to the extension of
the airport runway. The locations
and distances are
shown in Fig. 6, where h
is the altitude of the aircraft
from X. The X is the
nearest position of the train
to the navigation station,
where the navigation signal
is most vulnerable; and
ds1
, ds2
Fig. 5. Screenshot of measurement data for EMI receiver and description of the parameters.
108
IEEE Instrumentation & Measurement Magazine
, and ds3
are the distances
from OBS, VHFCS,
June 2021
log ( )
2
10
10
10 fN f
i log ( )
 log ( )f E N fE10
i1
(12)

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