Seite 128 - TELE-satellite-1201

Basic HTML-Version

TELE-satellite International — The World‘s Largest Digital TV Trade Magazine
— 12-01/2012
control voltage) or horizontal
(18 V control voltage) signals
are transmitted. The sec-
ond ‘trick’ can be achieved
with the help of a 22 kHz
control signal which is used
to switch between low band
and high band frequencies.
For a typical direct-to-home
satellite the low band ranges
from 10.7 GHz to 11.75 GHz,
while the high band covers
11.8 GHz to 12.75 GHz. If the
receiver-generated 22 kHz
control signal is detected by
the LNB it transmits the high
band frequencies through
the coax cable to the receiv-
er, and if no 22 kHz signal is
sent, the low band frequen-
cies arrive at the box.
In summary, it becomes
quite obvious that a coax ca-
ble is only able to take care
of one scenario at a time
(vertical or horizontal low
band, vertical or horizontal
high band). For simple re-
ception setups with only a
single user these restrictions
do not matter at all. Things
only get messy as soon as
several receivers use a sin-
gle coax line for receiving
satellite television. What
happens if, for example, re-
ceiver 1 requests a horizon-
tal high band signal from the
LNB, while at the same time
receiver 2 requires a vertical
low band signal? In a first-
come, first-serve scenario
receiver 2 would have to do
with the range receiver 1 has
requested, if all that is avail-
able is a single line to the
LNB. This would by an abso-
lute no-go in everyday use
so that other routes have to
be chosen for unlimited re-
ception by all users in a mul-
ti-user system.
The method of choice so
far has been to use LNBs
with up to four outputs, each
of which can offer any band
and polarisation requested
by up to four separate re-
ceivers. If the number of
receivers hooked up to an
antenna exceeds that num-
ber, multi-switches need to
be installed which receive all
four reception bands/levels
via separate coax cables and
then distribute the signals
to any number of receivers,
with each user having full ac-
cess to all channels. Unfor-
tunately, what we just called
‘any number of receivers’ in
the previous sentence is in
actual fact a somewhat lim-
ited affair. Signal distribution
with multi-switches via coax
cables is subject to consid-
erable signal attenuation.
While this generally has only
negligible effects in smaller
set-ups of up to 10 outputs,
it can pose serious problems
if that number increases to
30, 40 or even more.
Now this is where the opti-
cal LNB from GlobalInvacom
comes into play. A stacker
that is built into the LNB
distributes all four recep-
tion levels (vertical low and
high bands, horizontal low
and high bands) on different
frequency ranges between 1
GHz and 5 GHz. After that,
the RF signal is converted
into a digital signal which is
then transmitted by laser via
a fibre optic cable. On the re-
ceiving end of the line a GTU
(gateway termination unit)
converter box receives the
digital signal and re-converts
it into a conventional satellite
signal that will be accepted
by all satellite receivers.
The GTUs are available
as Quatro or Quad models,
with the Quad versions de-
signed for direct connection
of receivers, and the Quatro
model for feeding an exist-
ing multi-switch distribution
system, as it provides each
reception level through a
dedicated output.
So what’s the big deal? No
big deal at all: A single 3 mm
fibre optic cable is enough
to distribute the entire fre-
quency range of a satel-
lite to any number (and this
time we really mean it!) of
receivers, with no need for
a 22 kHz signal for switch-
ing between the low and
high bands. The beam of
light travelling through fibre
optic cables carries all fre-
quencies at the same time,
so that each receiver within
the distribution network is
absolutely independent in its
selection of channels.
Even if you need to pro-
vide satellite television to
entire apartment buildings
or estates GlobalInvacom
has the perfect solution: A
single fibre optic cable is
led from the LNB to a cen-
tral distribution point where
the initial light beam is split
into several new light beams,
provide a number of
fibre connectors and
attenuators that assist
with the installation of a
fibre system. There are
Barrel Connectors and
Adapters designed to aid
a trouble free install and
attenuators of varying
values used when the
optical signals are too
strong (type, male to
1m FC/PC