Interference protection requirements for terrestrial microwave links in the UK private-user frequency bands

Many broadcast television circuits are carried on microwave links in the private-user frequency bands. At present the television signals are carried in analogue form. High data-capacity links would be required to allow television signals to be carried in digital form. The bandwidth available in the lower frequency private-user bands (which are more desirable as they allow longer hop lengths) is limited. As a result, more sophisticated, bandwidth-efficient modulation techniques are required. Systems using more than four amplitude and phase states are not currently used in the private-user frequency bands. Before they can be introduced the protection requirements for interference to and from each of the many different analogue and digital systems used at present in these bands must be determined. Described here is a set of experimental measurements and theoretical calculations to determine the interference protection requirements of dissimilar analogue and digital systems. Recommendations are made as to the most suitable method of determining the protection ratios required for interference between systems. This approach should be used to determine the protection requirements, both for new systems and existing ones. It is also recommended that the receive filter response should be specified and checked during type-approval tests and that the transmit spectrum masks should be modified to reduce the permitted level of out-of-band radiation.