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Old 17-Feb-2013, 8:24 PM   #1
GroundUrMast
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Some thoughts re. cable arrangement & splitter choices

Most of the threads in the Help With Reception forum involve more than one connected TV. In multiple tuner installations the choice of splitter and coax cable layout may be one of the issues that needs to be resolved. Occasionally, a TVF member describes a coax wiring arrangement that is less than ideal. For example, they may have the antenna run to a TV location where a splitter is connected... then more coax to another splitter to feed more TVs and so on. This daisy chain arrangement may have grown over time, as TVs were added. As they get to the end of the line, they find they have low signal levels. They may also want to add an FM antenna to the system but find the FM signals cause interference to one or more TV signals.

Best practice is to 'home-run' the coax from each TV, FM tuner and coax modem outlet to a common location. The antenna(s) and coax based internet service would also be run to this common location. This becomes a convenient place to make, break and rearrange connections. Ideally, the 'home-run' location, AKA the 'distribution point' would be;
Reasonably accessible for service.
Centrally located so that all coax runs would be somewhat equal in length.
Would have power available if a distribution amplifier is going to be needed.
And, ideally, the distribution point would also be fairly easy to run additional cable to or from in the future.
By using the 'home-run' method, only the coax cables that are in service need to be connected. This can provide for separate TV and FM signal distribution and even internet or data systems that may not be compatible with OTA signals if placed on a single shared coax run. Home run cabling is simply more flexible and reliable, and if there's a problem, easier to troubleshoot.

By using a home run cable distribution system, you make it easy to select a single splitter with just the right number of output ports. This minimizes total system loss. Consider a system with seven tuners. If the system was built using a single 8-way splitter, the total loss due to splitting would be around 12 dB (typical 8-way splitter insertion loss). You would also want to terminate the unused port with a 75Ω resistor cap. On the other hand, if you used daisy chained 2-way splitters to feed seven TVs, the loss through each splitter will affect all the TVs connected further down the line. Each 2-way splitter will add about 4 dB of loss to the system. So, ignoring any cable losses, the first TV would be fed at 4 dB down, the second at 8 dB down, the third at 12 dB down, the forth at 16 dB down, the fifth at 20 dB down the sixth and seventh at 24 dB down. Include the cable losses, and the system loss is even worse. Finally, if an upstream cable gets damaged, all downstream TVs are affected.

Generally, a single splitter is best for most systems. If you can't find a splitter with the exact number of ports needed, simply terminate unused ports with 75Ω resistor caps. For most OTA systems, splitters with 5 to 1000 MHz bandwidth are fine. In most cases, paying extra for more bandwidth is wasted money. There are a few exceptions that call for additional bandwidth, http://forum.tvfool.com/showthread.p...4772#post34772.

Exceptions to the 'use only one splitter' recommendation exist, for example, let's say you have four working TVs, two or three of them fed by fairly long runs of coax. You now want to add a fifth TV that will be a short run from the distribution point, It may work out best to use one of the outputs of the 4-way splitter to feed a 2-way splitter. Doing so instead of changing the 4-way to an 8-way saves you from increasing the loss on all runs by 4 dB. By using a 4-way with a 2-way downstream you can feed the existing long runs with no additional loss, and feed the shortest runs (that can tolerate a bit more splitter loss) from the outputs of the new 2-way.

Plan your distribution system to avoid unneeded loss. If possible, avoid the use of an amplifier. I'm not against using an amplifier when it's needed, but amplifiers add noise and distortion... they're not always helpful. When planning, RG-6 coax should have no more than 6 dB loss per 100'. Insertion loss of splitters should be no more than, 2-way 4 dB, 4-way 8 dB, 8-way 12 dB.

http://forum.tvfool.com/showthread.php?t=109
http://forum.tvfool.com/showthread.php?t=12955

Last edited by GroundUrMast; 16-Jan-2014 at 7:14 AM. Reason: sp.
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Old 17-Feb-2013, 10:08 PM   #2
GroundUrMast
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What to do if you're stuck with a daisy chain

Some TVF members may be 'stuck' with a daisy chain cable arrangement. Perhaps the cable is buried in the wall or under a slab, and no attic to run cable in.

Fairly common to larger systems such as hotels, motels, airports, etc., is a device known as a tap, or feed through tap. Examples: http://www.solidsignal.com/pview.asp...28cp2509-10%29, http://www.cencom94.com/subpage21.html, http://www.sonoradesign.com/home.php...get=commercial.

This devise is intended for daisy chain connection. The last tap in the run will need a 75Ω termination. This termination can be a 75Ω resistor cap, an attenuator followed by a tuner input or, if the levels are not too high, just a TV tuner.

Expect to loose 1 dB passing through. So as you go further down the line, you'll likely need a lower loss tap to deliver similar levels to each TV.

This system may work with no amplifier, if so, keep the system as clean and simple as possible. In large systems, it's likely that an amplifier would be needed, particularly if the line is long and has many taps. Specialty MATV distribution amplifiers exist for this type design, though a small system could be served by a consumer grade distribution amplifier.

If you find yourself forced into this arrangement... that is you've considered rewiring in a home run style, but simply have no way to do so, then you may be left with making do with a daisy chain of taps.

Here is a basic tutorial on Master antenna TV system design, offered as incentive to consider making the conversion to a home run system: http://www.dipolnet.com/basics_of_de...ems__bib05.htm

Last edited by GroundUrMast; 19-Feb-2013 at 4:14 AM. Reason: links & comment re MATV DAs
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