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TELE-satellite International —
The World‘s Largest Digital TV Trade Magazine
— 09-10/2012
— www.TELE-satellite.com
If a feed is used to transmit content
that is protected by copyright laws (for
example a rock concert with clearly
specified exploitation rights) TV stations
will go out of their way to make sure the
feed is fully encrypted. If the content is
in the public domain anyway the meas-
ures used by TV stations generally are
less stringent but at the same time lock
out as many potential viewers as pos-
sible.
Selection of satellite
Using a popular DTH satellite for feeds
always results in a comparably high
number of unintended viewers. In addi-
tion, the cost for using hugely popular
positions such as ASTRA 19.2° East
or HOTBIRD 13° East is enormous, so
why would a provider select these birds
for feeds in the first place? Dozens of
less known satellites are available for
that very same purpose and apart from
being considerably less expensive they
cannot be received by 99% of satellite
antenna owners.
In Europe, the most frequently used
satellites for feeds are EUTELSAT W2
at 16° East, EUTELSAT W3A at 7° East,
EUTELSAT W1 at 10° East or TELSTAR
12 at 15° West for feeds to and from
North America, ATLANTIC BIRD 1 at
12.5° West and PAS3R auf 43° West as
the westernmost option. Unless you own
a motorised dish or top-notch multi-feed
antenna you’ll be left without a chance
to receive signals from these positions.
MPEG 4:2:2
For many years, TV stations have tried
to lock out viewers from feeds using
modified colour sub-sampling. Digital TV
reception via satellite generally uses the
4:2:0 standard which is characterised by
identical colour sampling in both spatial
directions, similar to the system used
for compressed JPEG images.
MPEG 4:2:2, on the other hand, fea-
tures a slightly different colour sampling
process which distinguishes between
horizontal and vertical colour sampling.
Colour sub-sampling has its origin in the
analog NTSC colour system and is used
for digital video signals based on the
ITU-R BT 601 norm.
With MPEG 4:2:2 horizontal colour
sampling has only half the size of ver-
tical colour sampling, yet this differ-
ence does not result in different colour
resolutions for the two spatial directions
because of interlacing that is inherent
in the analog PAL and NTSC standards.
Special receivers are required to cor-
rectly process and display such sig-
nals and because these receivers are
designed for professionals only they
carry a rather hefty price tag and thus
are unaffordable for most amateurs.
However, most new Linux-based
receivers allow real-time streaming
of satellite signals to the PC using the
built-in network interface. On the PC
software decoders (which are available
from the Internet at little or no cost)
can take over decoding MPEG 4:2:2 sig-
nals and display feeds for DX enthusi-
asts.
Low symbol rate
This is a clever trick used to make
sure transmissions cannot be received
by just about anyone. Almost all DVB-S
receivers available today are able to
process symbol rates between 2 and
45 Ms/s, with the symbol rate denot-
ing the number of changes of state per
second of the carrier signal. This is not
to be confused with the bit rate which
specifies the number of bits transmit-
ted per second and thus is an indication
of the video quality of a specific chan-
nel. However, the two values are in fact
interdependent as a low symbol rate
automatically means that less informa-
tion can be transmitted and as a conse-
quence the bit rate used must also be
lower.
This means that using a low symbol
rate for feeds is a delicate balancing act
for TV stations. On the one hand they
want to lock out as many unwanted view-
ers as possible by using a low symbol
rate, but on the other hand too low a
symbol rate automatically reduces video
quality, which of course is an absolute
no-go in the professional world.
In the end, mainly symbol rates
between 5000 and 6000 Ks/s are used,
which does in fact leave out a substan-
tial proportion of DTH viewers, but still
allows transmitting a high-quality signal.
Naturally, there are some examples
for extremely low values, such as signal
feeds of some Italian channels on NSS7
at 22° West which use symbol rates
of way below 2000 KS/s and there-
fore cannot be received on most digital
boxes.
Well-known
feed hunters
from all over
the world:
Applesat from Beijing, China
Feed hunter Rini from
Amsterdam, Netherlands
Roy Carman from London,
England