Important Basics; Attenuation; Frequencies - Devolo dLAN 200 AVpro Project Manual

devolo dLAN® 200 AVpro Project Manual

2 Important basics

2.1

Attenuation

Coax networks, respectively signals that are transmitted via coax, experience an
attenuation effect, measured in dB (decibels). Each component and module on a
coax network has a specific amount of attenuation. If several components (splitters,
sockets, etc.) are installed in line, you can simply add the different attenuation
values.
Coax networks for TV transmission usually have an attenuation budget of 42 dB
behind the amplifier for the antenna signal. Thus, in practice all components behind
the antenna amplifier may only have a combined attenuation of 42 dB. Typically, a
well-implemented installation will never fully use the available attenuation budget.
An exceeded attenuation budget usually results in interferences in your TV
picture.
devolo dLAN 200 AVpro adapters provide an attenuation budget for the dLAN signal
of more than 60 dB. Thus, a dLAN data signal fed in behind the amplifier will still be
available at full capacity at the farthest socket. In terms of the cable length, you will
be able to bridge distances of up to 750 meters without loss using a dLAN signal on
a coax line.
2.2

Frequencies

Unlike antenna signals that are transmitted from sender to receiver in one direction
only (unidirectionally), the dLAN data transmission is bidirectional. The following
frequencies are used:
devolo dLAN AVpro adapters use a frequency range between 2 MHz and
30 MHz. Usually, this band will not be overlapped by antenna signals that use
frequencies of 85 MHz and up. It is rarely possible that frequencies over 47 MHz are
used to transmit antenna signals (the so-called band 1).
"Traditional" analogue TV signals are transmitted in a range up to 862 MHz.
Above and until 2400 MHz you can find the signals of the digital satellite
television.
The frequency band between 5 and 65 MHz (in Germany, other countries, like the
USA, use 50 MHz) is called feedback channel, because data is sent from the
endpoint to the provider, if DOCSIS cable modems are used. If the sub range
between 5 and 30 MHz is not used by other signals, it can be used to transmit data
using devolo dLAN adapters.
In rare and special applications (e.g. in pay-TV or minibar systems in hotels)
control signals are transmitted in the frequency range between 5 and 30 Mhz. If the
feedback channel is reserved for a signal (e.g. by a pay-TV system) a coexistence of
both services is usually still possible. For that purpose, the specific frequencies have
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