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1. Introduction to IRS
2. IRS Systems versus Older systems
IRS
Systems versus Older System IRS Systems can be designed to carry digital
signals and be capable of providing residents with broadcast services
from terrestrial and satellite sources. This is because that in the passage
of time the transmitters that currently provide signals may eventually
be upgraded. Terrestrial broadcasts cover just over 400Megahertz of bandwidth
and most older communal systems were originally designed to receive and
distribute signals within this bandwidth. By comparison satellite signals
occupy more than 4,000 megahertz of bandwidth and the existing systems,
that are to an older specification, are unable to distribute signals across
this bandwidth.
Most old systems are designed with "Tree & Branch" or "Loop" system configuration
as shown below:
In
the old style systems such as "Tree & Branch" signals are received through
a shared antenna that is then amplified by a head end amplifier and then
distributed through a "Trunk" cable that then picks up "sub-feeds" to
the outlet in the houses. In "loop-wired" systems the sub feed is looped
from house to house instead of one sub-feed to every house. The other
main down fall of older designed systems is that the older cables are
only "single screened" and this can let in interference that can affect
the digital reception.
IRS systems use a system configuration known a "Star wire"; double-screened
coaxial sub-feeds run from each system outlet to one or more common locations
creating a direct connection between each outlet and the system electronics.
The trunk cable form older systems is replaced by a five-wire backbone
to extend the star wire configuration if a larger system is being installed.
An IRS System whilst capable of receiving satellite reception will still
receive reception from land based transmitters and the following types
of terrestrial service will be able to be received in the fullness of
time if all land based transmitters are eventually upgraded to digital.
FM Radio 87.5 - 108.0 MHz
DAB Radio 217.5 - 230.0MHz (Digital Audio Broadcast)
Television 470.0 - 862.0MHz
A typical star wired configuration is shown below:
 Good
quality antennas for UHF, DAB and FM radio need to be mounted at the aerial
array on each building together with robust brackets and fixings in sensible
but discreet locations. Filters will be used where needed to block unwanted
signals or potential interference. The satellite signals are provided
by fixing a satellite dish (approx. 90cm diameter) onto the roof of each
building in a generally south facing location. The dish will be mounted
discreetly but there will need to be a clear line of sight between the
dish and the ASTRA satellite.
The
dish will be located at the same area of the terrestrial array and fixed
with robust brackets. The dish will be accurately aligned to ASTRA 28.2
degrees east to receive both low band (10.70 - 11.70 Hz) and high band
(11.70 - 12.75GHz) on both vertical and horizontal polarities. This allows
the 4000MHz of bandwidth to be subdivided into four sub-bands of around
1000MHz each before being transmitted to a receiver. A Quattro LNB on
the dish both amplifies and converts the satellite signal before it is
distributed to the head end amps and multi-switches. Multi switches process
the four sub-band signals and the terrestrial signals and are connected
by a single cable down to the outlet in the house.
Existing TV outlet plates in houses will then need to be replaced with
TV/SAT/DAB/FM triplex outlets.
3.
Locating Components of the system
4.
System Safety and features
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