By Stephen Shaw Applications Engineer, Noisecom
The implementation margin of a satellite communication system is defined as the degradation of the signal after travelling through the up and downlink equipment. In order to find this, an EbNo generator can first be used to carry out an IF loopback test of the modem in order to find bit error rate (BER) values at different Eb/No ratios. A plot of these values can then be compared with the theoretical curve for the digital modulation scheme being used. The resultant difference is termed the implementation loss of the modem, and this value is used as a reference level for the second part of the test, in which the implementation margin of the complete up and downlink is found.