Sky
digital is transmitted from the Astra satellites located at 28 degrees
East of true South. The signals are collected from the satellite dish and
bounced back on to the LNB (Low noise block) at the front of the dish. The
LNB plays a vital part in receiving the signals, it not only receives the
data but also downconverts it and amplifies it before passing the signal
on to the receiver. The signal is received in Gigahertz (microwaves) and
can be passed on to the receiver using metal pipework, this is clearly not
practical so a good quality double screened cable is used containing an
outer metal foil to keep the signals in until they reach the receiver.
Apart from dish alignment the majority of signal faults usually occur in
the LNB itself, loss of certain channels etc. We therefore give the
following explanation of the many things that can go wrong with the LNB.
A typical Sky digital LNB receives the signal in four separate ways and it
is the receiver which instructs the LNB which signal to pass on. This is
how it works. The four main signals needed to work the Sky digital
receivers are: Horizontally polarised (Low band), Vertically polarised
(Low band), Horizontally polarised (High band), Vertically polarised (High
band) this is why it is essential to use a universal LNB as it will cover
all wave bands.
How does the LNB know when to change? The receiver sends out
different voltages to power up and instruct the LNB as to what waveband is
required for a particular channel. If a vertical channel is required the
receiver will send out 14V and for horizontal channels 18V. To get the LNB
to receive signals in the upper band where most of the digital channels
are, a tone is emitted which will automatically switch the LNB to receive
high band signals. In most cases where a number of channels are not being
received it generally forms a pattern IE: It may be all the vertical
channels lost or horizontal channels which would appear to be a fault in
the LNB not switching polarities correctly. We have seen many instances
where customers cannot receive the Disney channels, these are broadcast in
the lower band and again is usually the fault of the LNB not responding to
the "tone off" instruction or the LNB has a limited bandwidth
and can only receive the medium to high band signals only. We will be
submitting in the near future a complete list of all Sky digital
frequencies and what groups of channels can be received on each frequency.
You will then be able to enter these details on your Sky receiver and see
the separate packages being received via the "services menu" and
"Add channels" sub menu. Plus if certain groups of channels are
not being received it is here that you can test all of the four incoming
wavebands by entering the relevant frequencies. We will be covering more
of this subject in the future, if you have any queeries in the meantime
please email us.
Here is a link you may find useful, it provides details of the full
channel listings on the Astra satellite together with a breakdown of the
information listed above Astra
Channel Listings |
