Results and conclusions of the 120 and 180 Mbit/sec digital transmission tests

Single channel and cochannel interference tests were performed on the OTS transponders at 120 and 180 Mbits/sec in order to test their suitability for inclusion in the European Communications Satellite (ECS). Ground stations were used to check breadboard model predictions of systems performance. Although at 120, band-edge effects were not considered, and at 180, transponder amplitude was absent, results predict degradation at high data rates for ECS. Additional degradation is expected due to multipath and adjacent channel interference. More data is required, especially since a demodulator, which comes within specifications in the back to back mode, may have problems in the real environment. Other aspects, e.g. absolute encoding, burst to burst power variation, and the 40% cosine roll of filters, also require further investigation.