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 Edge CoreCore ADM ISP2 ISP1 Corporate ATM/FR PSTN/ISDN Internet Access 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 = ; 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 =

Spectrum Allocation 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 Fréquence [kHz] Densité spectrale [dBm/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 log 10 A/B -3 dB ► A/B = ½ 10 -3/10 = A/B dBm –x [dBm] = 10 x/10 [mW] 10 dBm ► 10 mW 20 dBm ► 100 mW Log 2 (X) = Log 10 (X)/Log 10 (2)