Communal IRS

Page 2: IRS v 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 right:

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 right:

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.