Transmitting Combiners > Technical Overview

TRASMITTING COMBINERS

Transmitting Combiners (Multiplexers) are devices able to sum various inputs with different frequencies on a single output.
The main application in television broadcasting is the transmission of various channels on a single broadband antenna. (Other applications involve the separation in reception or simultaneous transmission and reception on the same antenna).
Separation of different frequencies by definition requires filters; most multiplexers are created starting from the same filters used in transmitters.

The construction of a power multiplexer entails meeting various requirements:

• The multiplexer must be able to sustain the total output power, resulting from the sum of the input powers, both as total thermal power and PEP (Peak Envelope Power).
• Losses must be extremely limited; for systems with many channels the losses depend on the cascade of many elements, and the difficulties increase.
• Return Losses must be elevated, and even in this case the more complex systems exhibit Return Losses which are the composition of the Return Losses of a cascade, thus they require very high precision of each component to obtain overall acceptable values.
• By definition the inputs need to be suitably isolated; poor isolation would cause losses and intermodulation. The difficulty of obtaining high isolation is connected to filter selectivity; the maximum challenge is represented by the combination of adjacent DTV channels, possible only with mastery of the best cutting edge technologies.