ZyXEL Communications PLA-470 V2 - V3.0.5 Guía de instalación descargar pdf (Pagina 177)

Figure 8.6 shows that the transmission channel can be viewed as N sub-bands

with their sub-carriers, all of them operating simultaneously and each conveying

part of the physical layer data.

Transmission Power of PLC Devices

The measured power of the signal emitted by marketed PLC devices is usually 20

dBm (measured in the 1 to 30 MHz band).

The power can be expressed by variables P or G:

PGP

==10 10

and log

where G corresponds to the gain (in dBm or dBi) and P to the power (in mW).

Table 8.3 gives the correspondence between the power and the gain.

Since the power limit is set to 100 mW (equivalent to 20 dBm measured in the 1-

to 30-MHz band) for the electrical networks’ PLC devices, the performance of the

transmission channels depends on the signal range.

To be in line with the regulations in terms of EMC (electromagnetic compatibil-

ity) laid down by the CISPR committee, PLC devices must limit their transmission

power. This transmission power is measured as a quasipeak value, and not as a

mean value. In the frequency domain, this corresponds to a PSD (power spectral

density), i.e., a uniform distribution of the total transmission power on all the fre-

quency sub-bands of the 1- to 30-MHz band.

158 Installation

Figure 8.6 PLC technology multichannel OFDM modulation

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ZyXEL Communications PLA-470 V2 - V3.0.5 Guía de instalación Pagina 177