Field and laboratory measurements of the screening effectiveness of CATV networks and DAB signal levels

DAB test transmissions in Helsinki, started in February 1994 on 105 MHz, were transferred to the final frequency 220.35 MHz (block 11C) in March 1996. This resulted in thousands of complaints to the Finnish Broadcasting Company (YLE) and to the cable TV operator in the Helsinki area. The picture quality of the second national TV channel had suddenly deteriorated to an unacceptable level in these households. This was due to the on-the-air transmission of the DAB signal on the same frequency which was used for the distribution of this TV channel in the CATV network. The CATV operator has connections with an organisation of the private telecom companies in Finland. Most of its member companies operate and own CATV networks in the towns and cities where they are located. Several of them will face this same situation, when new transmitters in the Finnish DAB network start operation. This organisation set up a working group to investigate possible solutions to avoid the repetition of the interference problem. As a part of this investigation, Technobothnia Laboratory in Vaasa was asked to perform measurements which would give this group information on the state of the CATV networks in use and on the levels of the disturbing DAB signal