Date post: | 22-Dec-2015 |
Category: |
Documents |
View: | 223 times |
Download: | 2 times |
EMC
Mohamed Mokdad
Ecole d’Ingénieurs de Bienne
Agenda
• Current situation
• EMC Theorie
• Equipement interaction
• Sprectrum allocation– National & International
• The twisted pair
Why EMC?
• WHAT IS EMC? ElectroMagnetic Compatibility: With the proliferation of electronic systems in every aspect of our daily lives, there inevitably comes the problem of compatibility. Listening to the news on AM radio while using an electric razor should not be a problem, as it was in days gone.
• WHY DO WE NEED EMC? If EMC design practices are adhered to by both the razor and the radio manufacturers, then listening to the news on an AM radio, while using an electric razor, presents no problem. Also, worldwide governmental regulations prohibit electronic products from emitting or being susceptible to, Electro-Magnetic Interference.
Netzwerk-Architektur Transport
EdgeEdgeCoreCoreCoreCore ADM
ISP2 ISP1
Corporate
ATM/FRATM/FR
PSTN/ISDNPSTN/ISDN
InternetInternet
AccessAccess
ATM Switch/IP giga-router
Transport
Routers
Point-to-point Microwave
Current access technologies
• Wired– Analog / twisted pair– Digital / twisted pair– CATV– xDSL– Powerline
• Wireless– WLL– Mobile ?
The EMC issues
• EMC– Very critical (Very costly in manufacturing)– Electromagnetic Pollution
• Spectrum allocation– Licencing process– Limited ressource– E.g. OFCOM role in UMTS
EM waves
EM Fields Principles
• Antenna receives all signals in the air– Depending on emitted power and
• Cabling acts as antennas– In receiving power and– In emitting power
• Antenna is optimised for frequency ranges
• Filtering helps selecting bands– E.g. Radio station selection
Spectrum and media
• Wireless– Services are allocated frequency bands
• Wired– Services have to be
• Immune against neighbouring services• Not disturbing for neighbouring services
– How• Cabling is radiating power• Cabling is capting electromagnetic fields
Perturbations
• Magnetic Flux = (Flux Density) x (Loop Area)
• For a steady state signal of frequency f, the induced
voltage in the loop is:
Induced Voltage = j 2 x π x (f ) x (Flux) ;
where – π = 3.14159; and j denotes 90 degree phase angle– f = Frequency of the magnetic field
Induction Concept
E.g. 2G Mobile telephony Spectrum
E.g. 3G Mobile telephony Spectrum
Le régulateur
Frequency vs. Wavelength
wavelength x frequency = speed of light = 300 000 000
Spectrum Allocation
10 000 cm 3 MHz
EMC Design
• Sprectrum optimised allocation– Global coordination (ITU)
• Cabling optimisation (Immune/No Radia.)
• Coupling reduction– Design and emitted Power (Reach range)
• Filtering – Costly by manufacturing– Passive– Active
Spectrum usage in access network
-140
-120
-100
-80
-60
-40
-20
0
1 10 100 1000 10000 100000
Fréquence [kHz]
Den
sit
é s
pe
ctr
ale
[d
Bm
/Hz]
Analogique
ISDN
HDSL 2 paires
HDSL 3 Paires
ADSL
VDSL
HDSL 1 paire
An Example: The Twisted Pair
Tight Twisting
The Result
When current flows in a wire, an electromagnetic field is created which can interfere with signals on adjacent wires. As frequency increases, this effect becomes stronger. Each pair is twisted because this allows opposing fields in the wire pair to cancel each other. The tighter the twist, the more effective the cancellation, and the higher the data rate supported by the cable. Maintaining this twist ratio is the single most important factor in any successful UTP installation.
Definitions
• dB– R [dB] = 10 log10 A/B
-3 dB ► A/B = ½ 10-3/10 = A/B
• dBm– x [dBm] = 10x/10 [mW]
10 dBm ► 10 mW20 dBm ► 100 mW
• Log2(X) = Log10(X)/Log10(2)