The Digital Television Group has confirmed that during trials held on the Crystal Palace transmitter, they established that a different transmission mode for digital terrestrial television would improve reception across the UK. However, it would reduce space for programme services.

Tests on three frequencies were carried out, following the closure of pay-tv service ITV Digital, using a 16QAM modulation and a different forward error correction rate. Currently, DTT transmits at the UK standard of 64QAM, 2/3 FEC rate.

The 16QAM modulation leaves less space for programme services but allows far greater reception. DTT has suffered problems with blanking pictures and stuttering audio, particularly when customers were too far away from the transmitter; a factor that many analysts believe played a part in poor subscription figures for ITV Digital. Simply turning up the strength of the digital signal was not an option, due to possible cross-interference on other frequencies.

Companies involved in the trials, which have now moved into a second phase testing 8k 16/64QAM transmissions, include BBC R&D, Crown Castle, ntl:broadcast, Philips, Grundig and Nokia. The DTI is part-funding the work.

More details are available in the full report on the DTG website.