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Discussion Starter · #1 ·
Hi,


I need help in distributing cable signal to 12 outputs (3 in 3rd floor, 5 in 2nd floor and 4 in 1st floor). How should I go about it? I was thinking of the following:


Input will be boosted through a signal amplifier (1 input to 1 output). This will be connected to a splitter 1 input to 3 output. Each of the outputs will be connected to each floor of the house.


For the 3rd floor I will connect it to a splitter 1 input to 3 output, 2nd floor 1 input to 6 output splitter and 1st floor will be connected to a 1 input to 4 output splitter.


Is this OK. Will I experience significant loss in quality? I was told I would have to use a tapoff. What is a tapoff?


Please help.
 

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Quote:
What is a tapoff?

Taps are devices similar to splitters the difference being you would run your cables in series the tap has an output which you would connect to another tap and so on. (in your case I would use 2 taps and one splitter).

First I would take the main cable and feed it into a 4 port tap then take the output of the tap and cable it to a 5 or 6 way tap on the 2nd floor, then cable the output of the 2nd tap to a 3 or 4 way splitter on the third floor.


You may or may not need an amplifier try it with out and if your signal is weak add an amp.

Remember all the signals are in a series config and if you have any unused ports on any of the taps or splitter terminate them.


Let us know how you make out.


Another option is to use a distribution amplifier on the first floor and run of the outputs to a tap on the second floor and then run the output of the tap on the second floor to a splitter on the third floor.
 

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Quote:
Originally Posted by skoka123 /forum/post/0


Hi,


I need help in distributing cable signal to 12 outputs (3 in 3rd floor, 5 in 2nd floor and 4 in 1st floor). How should I go about it? I was thinking of the following:


Input will be boosted through a signal amplifier (1 input to 1 output). This will be connected to a splitter 1 input to 3 output. Each of the outputs will be connected to each floor of the house.


For the 3rd floor I will connect it to a splitter 1 input to 3 output, 2nd floor 1 input to 6 output splitter and 1st floor will be connected to a 1 input to 4 output splitter.


Is this OK. Will I experience significant loss in quality? I was told I would have to use a tapoff. What is a tapoff?


Please help.

While using taps is the less costly route, your idea is workable.

If we use a figure of 10dB feeding your house, purchase a signal amp to boost an additional 15dB (for a total of 25dB). Your 3 output splitter will feed each floor. Use an unbalanced 3-way.


Use the -7dB leg to the 3rd floor. Then use a balanced 3-way. Each tv receives about 12.5 dB not including cable length loss.

Use the -3.5 leg to the 2nd floor. A 6-way will have roughly -10dB each leg thus each tv receives about 11.5 dB (again, not including cable length loss).

Use the other -7dB leg to the 1st floor. A 4-way will net each tv 11dB not including line loss.


IMO, keep the dB value of each tv in the positive 1 to 10dB range. Your plan should achieve this.
 

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Discussion Starter · #5 ·

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Originally Posted by RCbridge /forum/post/0


Taps are devices similar to splitters the difference being you would run your cables in series the tap has an output which you would connect to another tap and so on. (in your case I would use 2 taps and one splitter).

First I would take the main cable and feed it into a 4 port tap then take the output of the tap and cable it to a 5 or 6 way tap on the 2nd floor, then cable the output of the 2nd tap to a 3 or 4 way splitter on the third floor.


You may or may not need an amplifier try it with out and if your signal is weak add an amp.

Remember all the signals are in a series config and if you have any unused ports on any of the taps or splitter terminate them.


Let us know how you make out.


Another option is to use a distribution amplifier on the first floor and run of the outputs to a tap on the second floor and then run the output of the tap on the second floor to a splitter on the third floor.

I am not sure I get the difference b/w a tap and a splitter. Is there some pictorial representation somewhere on the net on the usage of a tap vs a splitter?
 

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Discussion Starter · #6 ·
Thanks for the replies so far.


I have gone through some of the other threads too. I contacted cabletvamps.com and they say I would need a different RF split for India (PAL system) and they do not sell them. (How I wish there was just one video system in the world!)


Any idea what kind of splitters, amps and tapoffs I would need and possibly where they are avialable.
 

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Tap versus splitter.


A tap is like a splitter with the difference being it (a tap) has it's taps (some value lower than the total power) and an output which is typically a few db less then the input.

Keep in mind each Tap (leg) will have a higher loss value when compared to a splitter.

The advantage of this allows you to cascade more taps in series so the power presented to the next tap is only a few db lower than the previous tap.


I hope this is clearer then mud!!

I will try and point you to a reference which should explain it better.
 

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The engineering term is "directional coupler". You "tap" off a portion of the signal from it for your TV and pass the rest down the line.


A splitter is a form of directional coupler that has equal value "taps" at the output side. In other words, 2 outputs (each 1/2 power or 3 dB loss), 3 outputs (each 1/3 power or 4.77 dB loss), 4 outputs (each 1/4 power or 6 dB loss).


A directional coupler could have a single 20 dB tap (1/100 of the power). This is commonly used as the drop into your house from the cable system up on the pole. Does this mean that the next guy in line gets 99% (what remains)? Absolutely.


That's why you have to balance how many customers vs. how many amplifiers to deploy out on the street. It's also why there are problems when you have new customers added to old systems. Each new user drops everyone else down a bit. It's not a problem until the design limit is exceeded.


Some info is missing here. Taps (directional couplers), etc. have no dependency on the type of signal passed through it. The frequency range of the "India" system is what's needed, not that it's PAL.
 

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Discussion Starter · #9 ·
Thanks a lot to both GeekGirl and RCbridge. Though it is still not crystal clear I am getting there.


What the splitter does is pretty clear. 10 outputs then each will have a signal strength of 10% of the input.


In case of a TapOff of10 outputs then the output where the signal is tapped off gets 10%. What is unclear to me is what happens to the remaining 90% if they are not connected. In other words I have a Tap with 1 input and 10 outputs, only two of them are connected then will each of them have 50% signal strength? Is this what RCbridge was referring to as Series? (I guess the splitter is parallel then!!!)
 

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One more shot:

Since you understand how a splitter works, the tap is designed to pass some of the power to the next device in line (series) so in doing this each tap will have a loss larger then a typical splitter.

Ex 4 way splitter (power divider) each leg has about a 7db loss, If power in = 0dbmv then each leg will have about -7dbmv.


A 4 way tap can be designed to take the same 0dbmv in and provide each tap with a greater loss then the 7db of a splitter and pass on the extra energy to the next device in line (series).

Ex if I have a tap value of 10db (compared to the splitter which was 7db) I have that additional 3db of power to pass on to the next device (in series with the tap) this is what comes out of the tap.


You can design the tap to have more loss per leg and pass on more power.


If you have a 10 way tap each tap will only get some percentage of the total power this is a fixed value so if you don't use all of the taps that value won't change, but you must load the unused taps with terminations.
 

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Quote:
Originally Posted by GeekGirl /forum/post/0


Some info is missing here. Taps (directional couplers), etc. have no dependency on the type of signal passed through it. The frequency range of the "India" system is what's needed, not that it's PAL.

The only difference is in the connectors. Most PAL (and probably SECAM) countries use the same "F" connectors on their satellite cabling, that we do here in the US.


For "antenna" or broadcasting band (VHF/UHF), they use a different connector, which has a larger, captive pin....or a socket. There are actually male and female connectors, which keep you from plugging, say, a VCR in backwards, with the antenna connected to the modulated output and the RF input connected to the TV's tuner.
 

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Think of taps and splitters using "the water analogy", something we used a lot in school.


Most people seem to think a splitter is like a "Y" with the same size of pipe coming out both "spigots" as what went in. In reality, the "pipes" coming out (of a two-way splitter) are each 1/2 the area of the one going in.....so it gives about 50% of the incoming "flow" to each output, minus a bit for "turbulence" or heat losses ("friction" or "turbulence" in our water analogy).


A tap is much like the water distribution in your neighborhood. The big "pipe" (like a water main) has a much smaller "tap" coming off it (and often, you have some kind of regulator on your water line). Lots of water flows through the main, and a specific amount is tapped off for your house, with the rest of the main feeding similar setups at other homes.


An RF tap siphons off a specific amount for it's own distribution, letting the rest pass down line. Some taps siphon off just enough to drive one set, others siphon off enough for several sets, using a built-in splitter to further divide the signals.


Either way, you can't put ALL the water through the small pipes, and you can't put all the RF thru each of the splitter or tap outputs.


You have to design the system for proper levels at the final outputs (that feed the TV sets), by computing the total losses of all the taps, splitters, and cable losses....usually the highest frequencies are what you use in computations. Using "dB's" (decibels) is the shorthand that we use. 3 dB is about 50% of the power. A 2-way splitter (all splitters are just cascaded 2-way splitters internally) looses about 3 dB plus a bit of friction/heat loss to each output, so, about 3.5 dB. A 4 way looses 3 dB+3 dB+ heat loss, or about 7 dB.

And so on.


So, say you want a +6 dBmV level at each set, you'd need to make +9.5 dBmV at the input of your 2-way splitter, or +13 at the input of your 4-way, or +17 at the input of an 8-way. The trick is to keep things balanced, too. So, always divide things equally, or use various taps (they come in different "tap off" levels) to keep levels balanced along a feeder line.


You'll need an appropriately "sized" amplifier to make up the difference between the incoming signal and the signal at the end of all those taps and splitters, which you computed by adding all the losses.
 

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Discussion Starter · #13 ·
OK. I think you have all successfully managed make me understand the difference b/w a splitter and a tap. Thanks...


Now I do believe the TV technician who said that the Taps have to designed along with the usage of the amplifier and the splitter was not bluffing. OK, if using a Tap is so complicated why one choose a Tap over a splitter. Specifically in my situation isn't an amplifier and three splitters enough, taking the formula dB = 10 * log(n) where n is the number of outputs of the splitter into consideration?


Two more questions:

1) Does it really matter whether I use a PAL signal or NTSC so long as it is 75 ohms?

2) Does the logic of amplifiers and splitters work the same with a Satellite Dish such that I just need one Dish and as many settop boxes as the TVs?
 

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Quote:
OK, if using a Tap is so complicated why one choose a Tap over a splitter. Specifically in my situation isn't an amplifier and three splitters enough, taking the formula dB = 10 * log(n) where n is the number of outputs of the splitter into consideration?

I don't understand the complicated part of it, using a tap in place of a splitter for needs such as yours allows for a more even distribution of the available power.


The difference in power level at the first split compared to the last split will be much greater when using a splitter over a tap.

Do the math. You stated a 3 way split then a 6way split and last a 4 way split.

Start with 0dbm and work your way through your scenerio (regardless of the starting power level) the difference of the input to the last stage will remain constant.


Using taps (take a tap with a 2 db insertion loss) and work out the numbers.
 

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Quote:
Originally Posted by skoka123 /forum/post/0


taking the formula dB = 10 * log(n)

Just out of curiosity, where exactly did you obtain the above formula? The reason I ask is that I referenced the site you quoted, cabletvamps, and they are using the incorrect formula for their 15dB amplifier. It should be dB=20*log E1/E2 where E is the input and output in mV. Their claim of 32x reference level uses the power ratio of 10*log instead of the voltage ratio of 20*log. It should state about 5.6x reference level. For what its worth.
 

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Discussion Starter · #16 ·

Quote:
Originally Posted by RCbridge /forum/post/0


I don't understand the complicated part of it, using a tap in place of a splitter for needs such as yours allows for a more even distribution of the available power.


The difference in power level at the first split compared to the last split will be much greater when using a splitter over a tap.

Do the math. You stated a 3 way split then a 6way split and last a 4 way split.

Start with 0dbm and work your way through your scenerio (regardless of the starting power level) the difference of the input to the last stage will remain constant.


Using taps (take a tap with a 2 db insertion loss) and work out the numbers.

Well the complicated part I was referring to is that I need a qualified technical person to design the Tap for me and make sure the output levels are matching. In case of a splitter probably I could do it myself.


On further thought, it seems like it will be worth the effort to have a technician do it for me and this theoretical background has given enough knowledge to bug them. The major advantage I see with an Amplifier + Tap combination is that I can have a really fat pipe (read will lots of signal boosting) and then have a Tap just wide enough to let much signal as is required per TV.


I truly appreciate your patience.
 

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Discussion Starter · #17 ·

Quote:
Originally Posted by Kolchak /forum/post/0


Just out of curiosity, where exactly did you obtain the above formula? The reason I ask is that I referenced the site you quoted, cabletvamps, and they are using the incorrect formula for their 15dB amplifier. It should be dB=20*log E1/E2 where E is the input and output in mV. Their claim of 32x reference level uses the power ratio of 10*log instead of the voltage ratio of 20*log. It should state about 5.6x reference level. For what its worth.

3dB = 10*log(2)

4.8dB = 10*log(3)

...


That is, for a one input two output splitter I need to feed +3dB to get 0dB out. For a 3 output splitter I need to feed +4.8dB to get 0dB out. This is what I understood from one of the posts by GeekGirl on another thread on this forum ( http://www.avsforum.com/avs-vb/showt...&post8397060 ) and it seemed to match with specs at http://www.electroline.com/en/produc...fications.html .


I am assuming that I can use this as a general thumb rule.
 

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Quote:
Originally Posted by skoka123 /forum/post/0


3dB = 10*log(2)

4.8dB = 10*log(3)

...


That is, for a one input two output splitter I need to feed +3dB to get 0dB out. For a 3 output splitter I need to feed +4.8dB to get 0dB out. This is what I understood from one of the posts by GeekGirl on another thread on this forum ( http://www.avsforum.com/avs-vb/showt...&post8397060 ) and it seemed to match with specs at http://www.electroline.com/en/produc...fications.html .


I am assuming that I can use this as a general thumb rule.

I believe you are confusing the posters remarks and equations. One does not use any equation to achieve 0dB out from a splitter. If you use a 2-way splitter rated at -3.5dB per port, simply feed +3.5dB. Same for a 3-way. A balanced one is rated for -5.5dB per port. Feed +5.5dB to achieve 0dB.


As stated, the electroline site is using the wrong equation. They state +3dB= 2x reference level. This is a power ratio not a voltage ratio and is frequently confused. For example, if you increased your receiver from 500 watts from 250 watts, this is a 3dB increase (+3dB doubles your power. Power equation: dB=10 log power1/power2). If you asked for an amplifier that is 32x reference level, you would receive one with +30dB (when you actually needed a +15dB amp) and would seriously over amplify your set up. (Voltage equation: dB=20 log mV1/mV2)
 

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One more important piece of info into this fray. The satellite dishes need DC to feed the LNB. Using an RF splitter that does not have a DC pass-through will fail. There are splitters designed for satellites (rated for DC - xxx MHz).


The whole "dB" thing is a mathematical convenience so we can add and subtract instead of more complicated multiplcation and division. From this log identity: log(x * y) = log(x) + log(y). The "dB" is a ratio, named after Alexander Graham Bell. A "Bell" unit is very large, so we use 1/10th of that or a deci-Bell. That's why the "10" * log(). Hit google for historical references.


Since a dB is a unitless ratio, the 3rd letter refers to an absolute reference. For example, a 0 dbmV is the ratio referenced to 1 mV into 75 Ohms which is a measure of power, (1 mV^2)/75 = 13.3 nW. These are agreed upon industry standards. We use 10*log() for power. Since voltage is V^2, that's the same as 2*10*log() = 20*log() as mentioned in Kolchak's equations. More than enough math, but it's the right background for the problem at hand.


kenglish - nice water analogy. The terminations are used to keep the backwash turbulence from entering the main system flow. They soak up the reflections caused by an open port. Without them, the other signals get a bit perturbed...
 

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Discussion Starter · #20 ·
In India currently we have three Satellite TV providers (commonly known in India as DTH operators). A fourth provider had to postpone their plan as the satellite had failed. Digital Cable (not the HD type) has also started rolling out recently.


To add to this confusion there are three more companies that are planning to roll out IPTV nationwide they are currenlty in the testing phase.


I have two main cables running through the house. I plan to connect one to cable and one to satellite dish. So I do understand that I would be needing different type of RF splitter for Satellite dish. Can the RF splitter that is used for Satellite Dish be used for cable also?
 
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