11-02-2021 07:14 PM - last edited on 11-04-2021 08:17 AM by LawrenceC
The numbers on the splitters (5.5, 3.5...etc.) represent attenuation.
A simplistic explanation is that coaxial cable, splitters, connectors and other hardware attenuate signals. Installers will add up all of the losses to determine if an installation will function properly.
In residential home settings, where coaxial cable runs are relatively short, the ratings are not as important as if an installation was being done in an apartment complex where cable runs would be longer coupled with more splitters & connectors.
A member of an Interconnect-centric forum that I'm an Admin on posted some good information concerning coaxial cabling.
I think that the information presented is ok for posting here.
For the sake of simplicity lets say that you have +10dbm at the ground block (or video output of the FiOS ONT). +10 is what we would normally shoot for to supply each house. Then figure that at each cable box you want between 0dbm and no less than -10dbm. That range is what cable boxes are designed to operate with. We're going to ignore signal "tilt", which is the difference in levels between the lowest and highest carriers, as well as the return signals from the cable boxes back to the system.
So now it's just a matter of simple math.
If you don't know a 2-way splitter has a 3.5db attenuation from the in to each of the outs. A 3-way comes in two varieties. Either symmetrical or with a "hot"port. Either it's -7 all around or there is a -3.5 port with the rest -7. A 4-way is just two 2-ways. So -7db from the in to the outs.
Now look up the specs for the cable you are using. Look for the attenuation at 1000Mhz, for the Belden 1189A it's 6.55db/100ft. It's given per 100ft so divide it down to per foot (.065/ft). Now determine all your individual cable run lengths and where they go.
Get your pencil and paper out and start with +10. Subtract .065 per foot for the length of cable between the ONT and the first splitter. Subtract 3.5 or 7 for the 3-way splitter. Subtract from that number .065/ft for each cable run from the splitter to the cable boxes. Do you end up with between 0 and -10 at each device? If so all good!
Hint- it's a good idea to make a drawing starting at the ONT of how you have your splitters connected along with cable lengths and where they go. That way you can write your levels at each point in the chain.
Tip of the hat to hbiss for providing the information.