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The coaxial cable used to connect the LNB and the BUC should have a 75 (ohm) impedance and typically should be either an RG-6 or RG-11 cable. The decision made regarding which of these two types to use is one of cost vs. performance.
The RG-6 cable is cheaper than the RG-11, but also suffers greater signal reduction. The RG-11 cable is usually more expensive, but provides a higher signal transmission performance. This performance difference should be considered when making any decision, along with any loss that may result from a larger distance between the iDirect Satellite Router and the antenna when making any decision.

I suggest simply that the choice of cable type be made on the basis of reading the installation instructions from the supplier. The instructions will normally indicate the preferred manufacturer and type of cable, depending on length and BUC power requirements.

If you are a potential customer ask what are the installation instructions?.  You might also ask if the cables provided come with loose or with pre-terminated F type plugs.  Axial crimp F connectors, which can provide a water resistant seal when used with a matching cable type need an expensive tool to close.

Any do-it-yourself F connector needs significant skill to do properly and must be sealed from moisture. Bear in mind that most in-service VSAT system faults are due to bad workmanship on the F connectors.

Best regards, Eric.