EMC’14/Tokyo
15P-B2
Electromagnetic interference examples of
telecommunications system in the frequency range
from 2kHz to 150kHz
Kazuo Murakawa, Norihito Hirasawa, Hidenori Ito, Yasunori Ogura
EMC Engineering Group
NTT EAST Corp.
Tokyo, JAPAN
Abstract— Recently malfunctions of telecommunication
installations caused by switching noises of electric equipment or
devices have been increasing. The switching noises usually have
low frequencies between 2 kHz and 150 kHz. This paper shows
some electric interference examples of telecommunication system
cause by ac mains noises in frequency range from 2 kHz to 150
kHz. This paper also shows a necessity of emission requirements
below 150 kHz for all equipment against EMC problems.
Power line
Keywords— switching noise, ac mains conduction noise, 2kHz
to 150kHz, EMI examples on telecommunication equipment,
emission requiremet
Telecom line
IINTRODUCTION
20ms/div
Fig.1 Measured noise wave shapes on a power mains and a
telecommunication line
P o w e r lin e
+ 30
PS (dBm)
It is important to reduce CO2 emissions by minimizing
equipment power consumption in the world. There are many
ways to reduce CO2 emissions, such as increasing power
circuit efficiency, reducing power consumption itself, and
using sleep modes. One way to reduce equipment CO2
emissions is to increase the efficiency of ac/dc or dc/dc
convertors. For these purposes switching power circuits are
used in electric equipment as well as telecommunication
installations and power systems. Initially, switching
frequencies were in the range of few kHz, but now switching
frequencies in the range of 2 kHz to 150 kHz are used in order
to increase efficiency and downsize power circuits,
particularly frequency transformers. A side effect is that these
power circuits become a source of electromagnetic noise with
a wide frequency range. This power spectrum noise causes
malfunctions of equipment connected to ac mains [1].
Fig.1 shows a measured noise wave shapes induced on
both an ac mains and a telecommunication line. An inverter
circuit of the heater generates a switching noise as shown in
Fig.1. Sharp pulse noises are generated on ac mains and large
common mode noises are induced on a telecommunication
line as shown in Fig.1. Fig.2 shows power spectrums of them
by using FFT (Fast Fourier Transform) analysis. According to
results of Fig.2, the noises have wide frequency ranges. In this
case, most of power spectrum is at frequency below 150 kHz
as shown in Fig.2.
0
- 70
+ 30
PS (dBm)
I.
T e le c o m li n e
0
-
10
100
1k
10k
100k
1M
F r e q u e n c y (H z )
Fig.2
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581
Power spectrums on a power mains and a telecommunication line
EMC’14/Tokyo
15P-B2
Fig.3 shows obtained noise sources of malfunctions after
investigations. There are many noise sources such as heaters,
lighting, elevators, electric vehicles and electric fences which
can cause malfunction of equipment as shown in Fig.3. Fig.4
shows investigated noise frequencies which cause equipment
malfunctions. According to Fig.3, a percentage of a frequency
range dc-150kHz is about 60%, 150 kHz-1MHz is about 24%.
This means low frequency noise problems still dominant. In
the following sections, two case studies related to
malfunctions caused by emission noises below 150 kHz have
been discussed.
Electric Heater
charger with 50-500Vdc is utilized for charging. The battery
charger is powered by 200Vac. In a customer premise, an
ADSL modem is connected to a personal computer (PC), and a
radio receiver is connected to 100V ac mains. These ac mains
are provided from two transformers for 200Vac and 100Vac.
There is another customer premise as shown in Fig.5. The
customer also uses an ADSL services. When the batter charger
operates, EMI problems occurred. Because many bit error
occurred on ADSL modem, then ADSL modem can not keep
network connection (Link Lost or Link down). 1.1 MHz
radiated emission from the battery charger caused a jamming
on not the radio receiver but also a radio receiver near by the
customer.
A customer premise
Otherwise includingunknown
EV
ADSL modem
SPD
Metal telecom line
DVD recorder
PC
Battery Charger
Lighting(LED)
→
AC Transformer
(6600 100/200V)
Radio
UPS
Noise sound
200Ｖ
Earth
100Ｖ
Transmission error
IP Equipment
Transmission speed down
Other customer premises
Water pump
Electric fence
Electric Vehicle TV booster
SPD
Earth
ADSL modem
ac Panel
Metal telecom line
AM Radio
Radio
PC
Earth
Fig.3 Noise sources that cause equipment malfunction
Fig.5 Telecom installation configurations of customer premises
1MHz>
0.15-1MHz
dc-150kHz
Fig.4 Noise frequencies that cause equipment malfunction.
II.
CASE STUDY 1
In this section, an example of ADSL service trouble caused
by an electric vehicle (EV) is discussed. Information for this
case study is shown as follows:
Service:
ADSL service
Phenomena: Bit errors, Link connection down
Noise source: Battery charger for EV
Victims:
ADSL modem, PC, Radio receiver
Fig.5 shows telecom installation configurations of customer
premises. In Fig.5, EV is an electric vehicle, and a rapid battery
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582
Fig.6 shows common mode conductive emission noise
wave shapes on ac mains lines and ADSL telecom lines at the
ADSL modem of the customer. After the battery charger starts,
conductive emission levels apparently increase, and the levels
are over 12Vp-p and 6Vp-p for ac mains and telecom line
respectively as shown in Fig.6. The voltage spectrum for noise
wave shapes is shown in Fig.7. In Fig.7, a horizontal line and a
vertical line show a frequency in Hz and a voltage level in dBV.
According to the result of Fig.7, emission levels apparently
increase between 10 kHz and 1MHz. This frequency range is
almost same of the signal frequency range of ADSL services.
In order to solve this EMI problem, we put a common
mode choke coil (CMC) on the telecom line and a noise cut
transformer on ac main of the ADSL modem as shown in Fig.8.
However, it is required to add ac main filter at EV dc charger,
because the emission level of EV dc charger is still high. Fig.9
shows an emission measurement result after additive
mitigations. In Fig.9, a horizontal line and a vertical line show
a frequency in Hz and a voltage spectrum in dBV, respectively.
According to Fig.9, measured conductive emission levels are to
be lower than those shown in Fig.8, and the emission level
difference between EV dc charger on and off is less than a few
dBV. After the mitigations, the link down problem of the
ADSL modem is also solved, however, the radio jamming at
the customer premise unfortunately remains because radio
emission level for EV dc charger is still high.
EMC’14/Tokyo
15P-B2
@Point A ac Mains (cold-E)
20
12Vp-p
ADSL Signal frequency band
（
Voltage spectrum(dBV)
Voltage V)
8
0
Charging starts
-8
Not charging
Charging
-140
6.25k 10k
100k
1M
（ ）
10M
31.2M
10M
31.2M
frequency Hz
[200ms/div]
(a) A conducting emission on telecom line
(a) A conducting emission on ac mains
20
Voltage spectrum(dBV)
8
@Point B Telecom line (L1-E)
Voltage V)
6Vp-p
（0
Charging starts
-8
Not charging
Charging
-140
6.25k 10k
100k
[200ms/div]
Fig.9 Voltage spectrum after EV dc charger mitigation
Fig.6 Common mode noise wave shapes on ac mains line and a telecom line
@Point B Telecom line (L1-E)
Power spectrum dBV)
ADSL signal band (26k
（ ）
(b) A conductive emission on ac mains
(b) A conductive emission on telecom line
0
1M
frequency Hz
III.
～3.75MHz ）
CASE STUDY 2
In this section, an example of VoIP (Voice over Internet
Protocol) service trouble caused by an electric heater is
discussed. Conditions of this issue are as follows:
（
Service:
-60
VoIP over FTTH (Fiber to the home)
Phenomena: Acoustic noise on telephone in cold seasons
-120
31.2
Charging
Noise source: Electric heater ( “DENKI KOTATSU”)
Not charging
Victims:
100
10k
1k
100k
Fig.10 shows a telecom installation at a customer premise,
where VoIP is provided by FTTH service. ONU/HGW is an
optical network unit and home gate way. CONT. BOX is a
controlling equipment for a door phone and a telephone. In a
winter season, an electric heater as shown in Fig.10 operated.
The electric heater is connected to ac mains. The CONT.BOX
and the telephone as well as the electric heater are connected
to same ac mains line. A cable between ONU/HGW and the
CONT.BOX is a LAN cable.
3.12M
Frequency (Hz)
Fig.7 Voltage spectrum of nose wave shapes
A customer premise
EV
SPD
CMC
Telephone, CONT.BOX
ADSL modem
Metal cable
PC
Door Phone
Battery Charger
Noise cut
transformer
CMC
IT
Radio
ONU/HGW
AC Transformer
(6600 100/200V)
→
TRF1
Earth
Telecom wire
Fiber cable
Telephone
TRF2
SPD
ADSL modem
Other customer premises
Acoustic noise
Earth
ac mains
Metal cable
CONT. BOX
Radio
Control wire
Electric
Electricheater
heater
PC
Earth
Fig.10 A telecom installation configuration at a customer premise
Fig.8 Additive emission mitigation on EV dc charger
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EMC’14/Tokyo
15P-B2
Fig.11 shows emission noise measurement results. Fig.11
(a) is a measured nose wave shape and Fig.11 (b) is a
calculated voltage spectrum of the noise wave shape at the
telephone. According to Fig.11 (a), the wave shapes have sharp
pulses with 10ms period. Fig.11 (b) also shows the noises of ac
mains and the telecom line is likely to be synchronized each
other. Fig.11 (b) shows the noises have a wide frequency noise
between 100Hz and 100 kHz. After investigation at the
customer premise, a noise source is an electric heater. It is
found that when the electric heater is switched off, the acoustic
noise can not be heard. A F2-1K filer (CMC, its center
frequency is 1 kHz) is put on the telecom line in order to
reduce the noise levels as shown in Fig.12. After the mitigation,
the acoustic noise problem has been solved.
IV.
CONSIDERATIONS
Fig.13 shows an emission limit of CISPR.15(1). In Fig.13,
a horizontal line and a vertical line show a frequency in Hz
and emission limits in dBuV. Calculated emission levels for
the case studies 1 and 2 including another example (an
electric fence) are shown in Fig.13. The emission levels
which caused malfunctions of telecom equipment exceed
limits (1)(2) at several frequencies as shown in Fig.13.
120
120
Disturbance limit voltage at ac mains (dBuV)
In a winter season, the customer said that acoustic noise can be
heard from the telephone, and in a spring season, the issue is
solved. After inspection, it is found that the acoustic noise can
be heard when the electric heater is on.
100
100
CISPR.15
NTT TR.174001
(Quasi peak limit)
808 0
606 0
404 0
EV (conducted voltage at ADSL modem)
Electric heater (conducted voltage at phone)
202 0
00
1.E+
10044
Electric fence (induced voltage at modem)
1 .E+0
55
10
1.E+066
10
Frequency (Hz)
1.E+7
07
10
1 .E+08
8
10
Fig.13 Emission requirement of CISPR.15
V.
CONCLUSIONS
In this paper, two case studies of EMI problems are
introduced. Broadband services, ADSL and PLC are widely
used in customer premises. For examples, ADSL signal uses a
wide frequency band between 26 kHz and up to a few MHz.
Switching or inverter circuits are usually used in
electric/electronic equipment, and these circuits usually
generate broadband conductive emission noises below 150
kHz as well as over 150 kHz. These emission noises of several
equipment are not always limited, then high level conductive
and radiated emission noise can transmit through ac mains and
telecom cables as well as air. These emission noises can cause
malfunctions or damages on telecom equipment as well as
electric/electronic equipment. CENELEC and CISPR or other
international bodies have started to study EMC requirements
below 150 kHz, but unfortunately the tasks have not finished.
Fortunately, CISPR.15 is one of existing EMC requirement
which covers below 150kHz. In any way, it is required to
establish EMC requirements for all equipment below 150 kHz
in order to establish appropriate electromagnetic environments.
(a) An emission noise wave shape
(b) A voltage spectrums for ac mains and telecom line at the telephone
Fig.11 Conductive emission noise
Door Phone
REFERENCES
ONU/HGW
[1] CISPR Publication 15, “Limits and method of measurement of radio
disturbance characteristics of electrical lightning and similar equipment 7th
edition”, Nov. 2005.
[2] CISPR Publication 11, “Industrial, scientific and medical equipment Radio-frequency disturbance characteristics - Limits and methods of
measurement 5th edition”, May 2009
CMC
CMC
Fiber cable
Telephone
ac mains
CONT. BOX
Control wire
Electric heater
Fig.12 Noise mitigation with CMC
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