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Old 2-Sep-2010, 7:41 PM   #9
Join Date: Dec 2009
Posts: 632
Originally Posted by acutshall View Post
You listed loss for cable and splitters, is there somewhere to find out the loss specs for the cable and splitters? i.e cable x has a loss per foot of...
Cable loss varies somewhat, so each manufacturer may post slightly different loss numbers (construction material, conductor thickness, insulator density, and other variables can make some cables slightly better/worse than others). Also, loss per foot does depend on frequency. Higher frequencies lose signal faster than lower frequencies. Connectors, kinks in the cable, and other imperfections will account for small amounts of loss too.

You really need to check the specs from each cable manufacturer to know what you're getting, but in most cases, I just go by the ballpark numbers as follows. Note that upper UHF frequencies have the most loss per foot, so we can just use this number to represent the worst case loss estimation in most setups.

RG59 : VHF ~4.5 dB/100ft : UHF ~9 dB/100ft
RG6 : VHF ~3.5 dB/100ft : UHF ~7 dB/100ft
RG11 : VHF ~2.5 dB/100ft : UHF ~4.5 dB/100ft

Splitters drop the power depending on the number of ways the signal gets split. Note that most 3-way splitter are actually 4-way splitters inside with the extra port terminated internally. Splitters are almost always constructed in even powers of 2.

1:2 splitter ~4 dB loss
1:4 splitter ~7.5 dB loss
1:8 splitter ~11 dB loss

After you have calculated the total cable and splitter losses for your system, you might want to pad the number by an extra dB or two to account for miscellaneous other losses (e.g., imperfect connectors, slight impedance mismatches, etc.).

You might find some cable manufacturers that publish slightly better/worse specs than others. In most installations, the cable lengths are typically not more than about 50 feet or so. For most people, that means that the difference between cable manufacturers is in the noise of overall system performance (maybe only 1 dB or only fractions of a dB difference).

There are other important points to consider when choosing between the different classes of cable (RG59 vs. RG6 vs. RG11).

RG59 does not have as much shielding as the others. If the cable runs parallel to a lot of electrical wiring or is in close proximity to "noise generating" appliances (e.g., microwave ovens, vacuum cleaners, etc.), there's a greater chance of interference leaking into the cable.

RG6 is available in standard and "quad shield" (RG6Q) versions. Standard RG6 is good enough for most situations. The "quad shield" versions are only required if electrical interference is higher than normal. Signal-wise, it doesn't hurt to have extra shielding when you don't need it, but RG6Q does usually cost more and the cable does increase in thickness and stiffness.

RG11 is significantly more expensive than the others. Since it is also much thicker than RG6, you need special (more expensive) connectors and crimp tools if you want to make your own cables.
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