Communications: Voice, Radio and Data - TV cable questions
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Wayne64
07-01-09, 12:56 PM
I have Cablevision and was wondering how much signal loss does one get using lots of splitters? Is there a right way to feed all the different areas of the house? My other question deals with those caps that go onto unused male connectors. Why does the center wire have continuity with the cap itself?
Gunguy45
07-01-09, 01:39 PM
Splitters lose about 4db per tap..so if you split then split again you lose 8db. You are normally better off splitting once and using say a 4 tap outlet then running to the TV/VCR whatever. A 3db loss is approx 1/2 the power.
The terminating caps have a resistor (50 ohm) to keep the circuit impedance correct. You'd need to measure it at a low range with a multimeter.
The terminating caps have a resistor (50 ohm) to keep the circuit impedance correct. You'd need to measure it at a low range with a multimeter.
Wayne64
07-01-09, 01:59 PM
Splitters lose about 4db per tap..so if you split then split again you lose 8db. You are normally better off splitting once and using say a 4 tap outlet then running to the TV/VCR whatever. A 3db loss is approx 1/2 the power.
The terminating caps have a resistor (50 ohm) to keep the circuit impedance correct. You'd need to measure it at a low range with a multimeter.
Thanks GunGuy, you have helped me in the past with other questions. So I should use those caps on unused taps? Also I'll do my best on cutting down on the splitter count but with 30 years of cable and two other owners they seem to be everywhere.
The terminating caps have a resistor (50 ohm) to keep the circuit impedance correct. You'd need to measure it at a low range with a multimeter.
Thanks GunGuy, you have helped me in the past with other questions. So I should use those caps on unused taps? Also I'll do my best on cutting down on the splitter count but with 30 years of cable and two other owners they seem to be everywhere.
Gunguy45
07-01-09, 02:05 PM
Yes, Its best to terminate unused taps or wall outlets. You might not really notice anything in a home...but its a good practice.
Rick Johnston
07-03-09, 05:43 AM
A couple of adjustments to Gunguy's numbers:
A two-way splitter will drop the signal to each output by 3.5dB. Every doubling of splitter ports at the same split location will double that loss: A four-way = -7dB and so on. A three-way can split evenly at -5.5dB, or it can have two outputs at -7dB and one at -3.5dB. Most splitters will have this "insertion loss" printed on the device. Insertion loss is cumulative, so if you have multiple splitters daisy-chained, add the values for each run of ports. For example, you have two 2-way splitters between the incoming cable and the TV: The first splitter's insertion loss is 3.5dB, and the second is 3.5dB = 7dB for that TV.
Cable length also must be taken into account. RG59 has more loss (higher attenuation) than RG6. It is also not an even drop across the entire frequency band. The higher channels (frequencies) are attenuated more than lower frequencies over the same distance. Distances as short as 100 feet can affect the signal by 3 to 7 dB. Distances are cumulative: Four 25-foot sections of cable between splitters adds up to 100 feet of cable. Here's a chart (http://www.northamericancable.com/techinfo/clc.asp) showing the attenuation at 100 feet. Today's cable systems generally top off at 900MHz.
Terminating resistors -- the "caps" you mentioned -- are 75 ohm, not 50. They are used to prevent egress and ingress, which is essentially noise. They are not required, but it's a good idea to terminate all unused ports. If you're terminating one port on a two-way splitter, it's better to eliminate the splitter and instead use an F coupler.
A two-way splitter will drop the signal to each output by 3.5dB. Every doubling of splitter ports at the same split location will double that loss: A four-way = -7dB and so on. A three-way can split evenly at -5.5dB, or it can have two outputs at -7dB and one at -3.5dB. Most splitters will have this "insertion loss" printed on the device. Insertion loss is cumulative, so if you have multiple splitters daisy-chained, add the values for each run of ports. For example, you have two 2-way splitters between the incoming cable and the TV: The first splitter's insertion loss is 3.5dB, and the second is 3.5dB = 7dB for that TV.
Cable length also must be taken into account. RG59 has more loss (higher attenuation) than RG6. It is also not an even drop across the entire frequency band. The higher channels (frequencies) are attenuated more than lower frequencies over the same distance. Distances as short as 100 feet can affect the signal by 3 to 7 dB. Distances are cumulative: Four 25-foot sections of cable between splitters adds up to 100 feet of cable. Here's a chart (http://www.northamericancable.com/techinfo/clc.asp) showing the attenuation at 100 feet. Today's cable systems generally top off at 900MHz.
Terminating resistors -- the "caps" you mentioned -- are 75 ohm, not 50. They are used to prevent egress and ingress, which is essentially noise. They are not required, but it's a good idea to terminate all unused ports. If you're terminating one port on a two-way splitter, it's better to eliminate the splitter and instead use an F coupler.
Gunguy45
07-03-09, 06:34 AM
Thanks Rick...too many years in Navy electronics..I have 50 ohms on the brain I guess..lol
And I don't think I ever noticed that about the multiple tap splitters...hmmm maybe I should go check mine.
And I don't think I ever noticed that about the multiple tap splitters...hmmm maybe I should go check mine.
Wayne64
07-03-09, 05:39 PM
Thanks for the additional input. Have a great 4th.
Rick Johnston
07-03-09, 06:12 PM
50-ohm terminations are still used in RF systems such as wireless mics. The preferred termination for RG58 cable is 50 ohms. All RCA connectors are 50 ohms. "ThinNet" BNC computer networks (like those Navy systems in the 90's) also used them, but they're rare these days. It's confusing.
As for splitter loss, it varies by manufacturer. Generally if you split a signal you lose half the power, which is -3dB to each side of the split. There is also an insertion loss from the device itself -- connectors and circuitry -- which is usuallly about half a dB on the better splitters. Taps and even simple connectors can introduce some loss.
Those seemingly tiny numbers aren't usually a big deal in a residential environment. There's about 15dB of play at most home subscriber drops. But when you're wiring a school with 250 TVs, or a hospital with 700 TVs, all of that stuff becomes critical. A couple of dB lost at one end can mean no picture in an entire wing at the other end.
Happy 4th back atcha!
As for splitter loss, it varies by manufacturer. Generally if you split a signal you lose half the power, which is -3dB to each side of the split. There is also an insertion loss from the device itself -- connectors and circuitry -- which is usuallly about half a dB on the better splitters. Taps and even simple connectors can introduce some loss.
Those seemingly tiny numbers aren't usually a big deal in a residential environment. There's about 15dB of play at most home subscriber drops. But when you're wiring a school with 250 TVs, or a hospital with 700 TVs, all of that stuff becomes critical. A couple of dB lost at one end can mean no picture in an entire wing at the other end.
Happy 4th back atcha!
Gunguy45
07-03-09, 06:24 PM
Rick...
The last paragraph you wrote hit home. When they first started putting TV's in berthing compartments, it was a real learning curve. We basically were called on to design and install these things with off the shelf componants..no training or recommendations. An antenna, 2 Channel Master amps..a couple of BetaMax VCRs and some spools of rg-58 (59?). Berthing all over from the bow to the stern, port and stbd and no direct routes between. Took quite a while and lots of questions before we could finally figure it out..let alone the guys who thought they knew better than us and tapped in with speaker wire and such...lol.
The last paragraph you wrote hit home. When they first started putting TV's in berthing compartments, it was a real learning curve. We basically were called on to design and install these things with off the shelf componants..no training or recommendations. An antenna, 2 Channel Master amps..a couple of BetaMax VCRs and some spools of rg-58 (59?). Berthing all over from the bow to the stern, port and stbd and no direct routes between. Took quite a while and lots of questions before we could finally figure it out..let alone the guys who thought they knew better than us and tapped in with speaker wire and such...lol.