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Splitter Info

You might want to understand how splitters and amplifiers affect your TV signal, and that is where we talk about dBs. dBs are a RELATIVE measure of how strong your signal is, versus how strong/weak it USED to be. 

For Example: You have a 2-way splitter connected to your incoming cable line. The marking on the splitter says 3.5dB. The 3.5dB marking really means that the signal coming out of the splitter will LOSE 3.5dB of strength. How much is that? In TV terms, there is a way of calculating this using a logarithmic formula. Instead of going through the formula, I have provided a table of some of the most common dB gain/loss values (TABLE 2), and their associated effect on your TV signal. So, getting back to our 2-way splitter - you end up losing 3.5dB or more than HALF of your original signal. It is calculated as follows:

Signal Loss Percentage = 1 minus (1 divided by dB power factor)
OR
% Signal Loss = 1 - (1 / (dB power Factor))

2-way Splitter Signal loss (percentage)

%Loss = 1 - (1 / 2.28)(2.28 is the dB power factor for 3.5dB)
%Loss = 1 - ( 0.44)
%Loss = .56 or 56%
Inserting a 2-way splitter decreases your signal strength by 56%.

 

4-way Splitter Signal Loss (percentage)

%Loss = 1 - (1 / 5.01)
%Loss = 1 - (0.2)
%Loss = .8 or 80%
Inserting a 4-way splitter decreases your signal strength by 80%.

What happens when you split your cable multiple times? This is how you would add up the two splitters in the example: 3.5dB loss + 7.0 dB loss = 10.5 dB loss 

The 10.5dB loss number is not in the table, so we'll estimate it another way...
We lose 56% of the original signal, then ANOTHER 80% of the remaining signal. 1- (0.56 * (1 - 0.80)) = 0.888 or 88.8% signal Loss. After these two splitters almost 90% of your original signal strength is GONE. By the way, if you know the 10.5dB loss number, the ACTUAL loss for a 10.5dB signal drop is 91%, so we were pretty close. It's no wonder your TV picture is so crummy, even after going through just ONE splitter, let alone TWO!

When shopping for an amplifier, bigger dB numbers are not always better. Too much of a good thing can actually make things worse for you. It is easily possible to make your TV signal WORSE by boosting the signal too much. This is called OVERDRIVING the signal. It is bad because it causes buzzing, bleeding or blotchy colors, and white streaks - among other problems. The best strategy is to keep the signal strength as close as possible to the signal strength provided by your cable company. In the real world this is done through painstaking calculations of cable lengths and cable splits throughout the house. However, most people don't know how to compute gain/loss so they take a SWAG (simple wild-ass guess) at it by throwing an amplifier in place, in the hope that it does what they want. Believe it or not, this actually works most of the time! If that were not the case, my feedback would certainly not be so good. Fortunately a good guess works for about 95% of the simple situations out there.

DECIBEL TABLE

dB Boost/Loss dB Power Factor Voltage or Current Ratio
0.0 1.00 1.00
0.5 1.12 1.06
1.0 1.26 1.12
3.0 2.00 1.41
3.5 2.28 1.50
4.0 2.51 1.58
5.5 3.55 1.88
7.0 5.01 2.24
10.0 10.0 3.16
11.0 12.6 3.55
15.0 31.6 5.62

Amplification (also known as dB boost): Amplification is the process of boosting a signal. Amplification is generally needed for homes with multiple TVs, or where long cable runs (>150 feet) are used. Amplification is generally a good thing, except for the fact that cheap TV amplifiers don't do a real good job, and can actually make the TV signal worse. Cheap amplifiers add "noise" to the signal, which can then be seen as ghosts, buzzing, snow, lines through the picture, and other annoying things. Good amplifiers do their job so well that they don't add ANY noticeable noise to the TV signal. Good amplifiers make your picture look BETTER, and don't cause side effects like ghosts, lines, or snow. The boost is measured in dB.

Example: Based on our Decibel Table above, a 1-port amplifier provides 15dB of forward signal gain, which means that the signal is almost 32 times stronger coming out of the amplifier than the signal going in.  In addition, a 1-port amplifier has a return path loss of 0.5 dB, which means it causes an 11% loss on any signal going back toward the cable company. Here is a quick summary table:

SUMMARY TABLE

# Amplifier Ports Signal Gain(dB) Forward Signal Boost Factor Return Path Signal Loss (dB) Return Signal Loss Percentage
1 15 31.6x 0.5 11%
2 11 12.6x 3.5 56%
4 7 5.01x 7 80%
8 4 2.51x 10.5 91%
4 (UG model) 0 1.00 7 80%
8 (UG model) 0 1.00 10.5 91%

 
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