ZyXEL Communications PLA-470 V2 - V3.0.5 Przewodnik Instalacji Pobierz pdf (Strona 40)

The signal frequency of a HomePlug 1.0 modem is between 4 and 25 MHz, giv-

ing a power spectral density of –50 dBm/Hz. We will examine the consequences of

this value in Chapter 8 (Table 8.10).

Table 2.2 summarizes attenuation values for the principal devices on the electri-

cal network.

Multiple studies have shown that in a household electricity distribution net-

work, the average signal attenuation is on the order of 50 dB/km.

Coupling Between Phases

When a high frequency alternating electrical signal is present on electrical wiring, it

provokes a magnetic field, called coupling, in the proximity of the wiring.

The coupling is known as crosstalk when the induction is between components

of the same electrical network and a telluric current when the components are in dif-

ferent networks.

Frequency Response

Depending on the nature of the electrical wiring (material, composition, age, and so

forth), its response to a high frequency signal, that is, its ability to propagate the sig-

nal, varies considerably.

We will spell out the consequences of this characteristic for the implementation

of a PLC network in Chapter 8 (Table 8.11), and show how they can be taken into

account when choosing network topology and electrical cables.

Interface Sensitivity

Electrical devices contain analog interfaces that permit their coupling (inductive or

capacitive) to the power line medium. In the case of PLC, these interfaces allow,

among other things, the transmission of a digital signal over electrical wiring.

Architecture of Electrical Networks 21

Table 2.2 Attenuation of Principal Electrical Equipment on an Electrical Network

Electrical equipment Attenuation Comments

Electromechanical meter 15 dB

Electromechanical meters attenuate the PLC signal

but do not block it, resulting in propagation of the

PLC signal outside of the private electrical network.

Electronic meter 15 dB Equivalent to the electromechanical meter.

Circuit breaker 5 dB

If a signal linking two PLC devices passes through

too many circuit breakers, it may be excessively

attenuated.

Power strip 10 dB

The construction quality of the power strip has a

great influence on its attenuation. Therefore, we

should avoid connecting PLC devices to power

strips.

Electronic meter and circuit

breakers

20 to 30 dB

The meter and circuit breakers combined do not

attenuate the signal enough to prevent its propaga

tion outside of the private electrical network of a

home or business.

Electromechanical meter

and circuit breakers

30 dB Above 20 MHz.

50 dB Below 20 MHz.

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