Spectrum Policies

The successful delivery of spectrum policies and the realisation of their potential is important for the Department,  and involves balancing the competing demands of different, though converging, sectors. Priorities must be determined and a way forward identified while recognising that there could be competing cross departmental sector policies that need to be taken into account, as spectrum is a major and critical enabler for the different sector developments.

The Digital Dividend is regularly referred to when the radio spectrum is being discussed. It is the spectrum (790-862MHz) that will be released following the migration of terrestrial television broadcasting from the traditional analogue transmission to digital transmission. This will occur in the UHF band in Ireland after 2012. 

Whilst the Irish TV services are now available by Digital TV to most of the country, since the number of services carried on Digital Terrestrial Television is less than had been anticipated, it will be possible to introduce other services into digital dividend sooner than had been anticipated.

As the manager of our spectrum resource, ComReg has a major role to play in ensuring that the success of this process is realised. ComReg has recently indicated (ComReg 10/59) that it intends to bundle the digital dividend spectrum with the existing 900MHz cellular telephony spectrum in a future competition.

In order to ensure compatiblity (see EBU article) between the new "LTE" mobile telephony systems (on frequencies previously used for analogue TV) and the Digital Terrestrial Television system, it is likely that some viewers will have to have a filter installed to reduced the strength of the cellular signal  at their TV or Set Top Box.
 
Filters may be needed in cases where the DTT signals are above channel 51 (due to potential so called image channel “N+9” sensitivity of some receivers) and in cases where channel 58 (770MHz) or 59 (778MHz) are to be used by DTT. That is installations using the "group C/D" type aerial. It is stressed that difficulties may only arise at locations close to LTE base stations.  Typical filters are being tested by ComReg, though for reception of channel 59 the filter will need to provide signal reductions above 790MHz whilst having a low loss in ch 59 (778MHz). ComReg has planned that ch 60 (786MHz) will not need to be used by the DTT services for which they are required to make spectrum available.  

The Saorview coverage checker can be used to indicate whether the DTT transmissions serving an area are likely to be in channel 51 or higher.

Mast Head Amplifiers

Installations which use a mast head amplifier for TV reception (irrespective of the frequencies to be received) will most likely need a filter. This is because mast head amplifiers are prone to an "overload" condition if the signal level from either DTT or other sources (on frequencies either above or below the TV signal) is very strong. In these overload conditions unintended signals called “intermodulation products” can be radiated causing interference to other users of the spectrum.

Mast head amplifiers should only be used for reception of DTT where there is a clear need to do so. Excessive amplification of a DTT signal can cause set top boxes to appear not to be able to decode the DTT service.



There is a lot to be done between now and the cessation of analogue television services in the UHF band. The Department will fully engage with ComReg and the other stakeholders involved in order to deliver the best results for Ireland.