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5. The Coverage Survey

BBc van

We undertook an assessment of terrestrial television coverage in the area in and around Weymouth and Dorchester between 31st May and 2nd June 2006 using a BBC spectrum planning vehicle.  The vehicle has a pneumatic pump-up mast with a TV receiving aerial on top that can be pumped up to a height of 10m, which is typical of the height of most rooftop aerials.  The vehicle also contains a complete set of technical equipment for measuring the received signals and this enables the TV coverage at the vehicle’s location to be determined.  This coverage will be very similar to that available at nearby houses.

Locations selected for our assessment were chosen as being representative of households where either analogue or digital terrestrial television reception was reported by viewers to be poor. This data was obtained from the questionnaire distributed and collated by SWEDBAG. 

Fig. 14 – The survey vehicle

The following summarises our main findings and observations:

  • There are many households with roof-top ‘Contract’ aerials that have probably been in place many years and in a number of cases are in need of replacing. Generally these ‘Contract’ aerials were dominant in areas where the field strength from the transmitter providing the strongest signal was in excess of 80 dBµV/m; in most of the areas we visited, the field strength exceeded this level. (Note: as a rule the field strength required for good analogue television reception is 70 dBµV/m.)

     ‘Contract’ aerials - these are usually manufactured and sold at low cost with the result that their performance is indeterminate and their lifespan is short.

      Field strength measurements and picture quality assessments are only reported here for analogue services.

aerial1

Fig. 15 - A ‘Contract’ aerial that is recognised by its basic construction and plate-type rear reflector

 

 

  • In general, analogue television coverage in the areas we visited is excellent with no impairment where good quality aerials are used.
  • The only area where terrestrial coverage was found to be poor is around Osmington.
  • In areas where viewers receive a lower signal level, good quality aerials together with masthead pre-amplifiers were seen to be used.
  • Charlton Down is an area undergoing significant building development with approximately 350 new dwellings. Some of these are on low-lying land and reception may be difficult; this can only be ascertained when the development is complete.
  • In the areas we visited, very few houses built within the past decade have roof-top aerials. We do not know the reason for this.  There may be planning consent issues or the houses may be receiving TV via satellite or cable.
  • Some houses without visible roof-top aerials may be making use of loft aerials.  The signal levels available from loft aerials are typically only 10% or less than those available from a comparable roof-top aerial (because of the lower height and losses introduced by roof coverings and insulation).  Broadcasters generally advise against the use of loft aerials for these reasons.  Where analogue reception is currently poor and to provide the best opportunity for DTT reception at the time of switchover, it would be best to replace loft aerials with ‘digital-ready’ rooftop aerials installed by a registered CAI[1] installer.
  • At the time of our visit, there was a high pressure weather system centred over the south-west corner of the British Isles. This may account for the Co-Channel Interference (CCI) we observed affecting analogue television reception in some areas.  We cannot be sure if these levels of interference are continuously present or if this was a rarity in the areas affected.
  • Local residents we spoke to during our visit reported that the quality of analogue television reception can be affected by Co-Channel Interference, and that it is weather dependent.
  • Analogue reception of Channel 5 is not available anywhere in the area.
  • Digital Terrestrial Television reception is currently not available to full planning standards in most areas investigated. However it is available in a number of locations on some digital terrestrial television multiplexes .
  • Satellite receiving dishes were seen on about 33% of homes in the areas we visited.

     A multiplex is a bundle of digital terrestrial television channels.  There are 6 multiplexes to transmit all the  Freeview DTT services.                                                

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