transmodulation

Transmodulation is the conversion of a signal into another modulation method. Transmodulation is required when a signal is to be fed from one transmission system into another, but the latter uses a different modulation technique.

In transmodulation, the signal modulated in one modulation method is first demodulated and then modulated again in the other method. Transmodulation is used, among other things, in the headend of cable distribution networks. For technical or economic reasons, a change is made from one modulation type to another.

Another example is satellite-based DVB-S, when this is to be fed into cable distribution networks. Here, the signal is received quadrature phase shift ke ying( QPSK), demodulated and modulated into quadrature amplitude modulation( QAM), which is more frequency-efficient for cable distribution networks.

Transmodulation is also important for set-top boxes, so that the subscriber can receive all programs with one set-top box using the same modulation technique.