This device is used for splitting and combining satellite quality co-ax cables such as WF100, CT100 or RG6. They are bi-directional for the video signals and so perform two functions. Firstly, they are used to split signals from the external antenna eg FM/DAB from the antenna or UHF from the aerial prior to decoding. Secondly, they can be used for combining decoded ouput from the modulated RF output of a VCR, a digibox or a modulator, prior to becoming the uplink to the distribution amplifier.
The relevance of the various types depends on the application for which you intend to use it. The bandwidth capability needs to be very high (up to 2400MHz) if you are working with satellite signals. In some cases you need to allow a DC electric current from equipment to power devices, eg the satellite LNB device or a remote IR receiver, whilst preventing this current being passed to other equipment, hence some versions have “DC blocking” or uni-directional “power-pass”.
All connections require the use of ‘F’ type fittings on the co-ax cable.