Until recently, analogue transmission technology was
the standard for TV and radio broadcasting. The main
drawback of analogue technology is the fact that only
one TV and four radio channels can be transmitted by one
transponder at a time. ASTRA I currently still uses around
40 analogue transponders, but their number will decrease
over the next few years. Analogue transponders on ASTRA
I have a significantly lower range than digital
Today, and even more so in the future, digital transmission
technology will play the predominant role in satellite
TV. The basic benefit to the programme providers is the
fact that several channels can be transmitted on a single
transponder, whereby the allocation can be freely selected.
Instead of 12 TV channels, broadcasters can also choose
to have just radio stations or a mixture of TV and radio.
Internet data transmissions and any other types of data
service are also possible. As well as additional flexibility,
this also offers considerable economic benefits for
The combined total of all digital data transmitted on a
transponder is referred to as a “transponder stream”.
This includes the individual TV and radio channels.
The transponder stream is what the receiver actually
receives. The frequently published frequency, polarisation
and symbol rate data always relate to a transponder
For analogue transponders, the bandwidth is set to
approx. 27 MHz. Digital transponders can be operated at
almost any bandwidth. This makes it possible to operate
older, weaker transponders with a reduced bandwidth and
still obtain a wider range. Furthermore, a single transponder
can carry several independent low-bandwidth signals
(transponder streams), an option which is used most
commonly by broadcasting vehicles. As a general rule,
broadband signals (MCPC - Multiple Channel Per Carrier)
tend to be used to supply signals to end customers,
while signals with lower bandwidths (SCPC - Single
Channel Per Carrier) are mostly used for relay
transmissions, so-called „feeds“. ASTRA 1 almost exclusively
transmits MCPC signals suitable for direct reception.
The symbol rate is an important figure to know, as it must
be entered correctly into the receiver to ensure a successful
channel scan if specific channels are to be searched.
The higher the symbol rate, the higher the bandwidth,
and the more channels can be transmitted on one transponder.
However, digital technology allows many other
ways to configure the transponder stream in addition to
the symbol rate. Some providers use this to squeeze a
higher number of channels onto one transponder, which
results in poor image quality, low range and an increased
Digital reception range
GThe range of each the individual transponders varies
slightly. This is sometimes used deliberately to focus the
signal onto one area, sometimes this occurs more or less
by chance. In addition to the transmitting power, the
satellite also plays a role, as does the transponder stream
configuration and the signal bandwidth. It is therefore
normal for some channels to be received at the edges of
the footprint, while other channels cannot be received
there. Of course, modern automatic systems only scan
digitally and therefore locate satellites from locations in
which only few channels can still be received. Systems
using an analogue search give away several hundreds
of km of range.
Interference on digitally received broadcasts
Normally, the TV image collapses almost instantly if the
signal strength is insufficient. Interference usually manifests
itself in the form of blocky/pixellated images or
frozen images. This usually indicates that the signal
strength is too weak. Other possible causes can include
transmitter errors or an overload of the transponder
stream. HOTBIRD often transmits channels which are
affected by noticeable
Clear view of the satellite
A clear view of the satellite is the key prerequisite for
good reception. Buildings within the signal beam always
block reception. Trees may, in rare cases, allow the signal
to pass through unhindered, but this is not reliable.
The geographic location also needs to be taken into
account, as the signal is received at a much flatter angle
the further north the system is operated. In very northerly
regions, the curvature of the earth can cause even topographic
obstructions like mountains to prevent reception
of satellite channels.
The larger the antenna is, the larger the reception range
will be for a given transponder, and the more tolerant
the system will be to poor weather. Damaged, i.e. dented
or warped antenna dishes reduce the range significantly.
High-quality LNBs show their increased capacity only at
the limits of the footprint. Even in the centre of a footprint,
e.g. in Germany, satellite operators recommend a
minimum size for the satellite dish in order to ensure good
reception even in poor weather.