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)