What Is Cable That Can Carry a Wide Range of Frequencies With Low Signal Loss?

How Long Tin I Run Coaxial Cable?

Written by Dave Harris, trueCABLE Technical Specialist

All solar day if you want to.

Dorsum in the olden days, when there were three channels on TV (four if you count the educational aqueduct), and closed-circuit transmissions consisted of low-resolution analog signals, it was possible to finer run coaxial cable for hundreds and maybe fifty-fifty a thou feet.  I'm sorry to have to tell you this, merely those days are pretty much over.

This bad news is due to the good things we have today that we didn't have back then, such as broadband Net and high definition digital tv (HDTV).  You see, the reason there are whatever limits at all to how far a cable can be effective is signal loss, also called attenuation .  Attenuation in coaxial cable is mostly due to cable construction, altitude of the circuit, and frequency of the point.  In brusk, for any given coaxial cable, the college the frequency of the signal, the shorter the distance until the signal loss is likewise great to make use of what's left of the betoken.  Digital broadband and satellite systems operate at very high frequencies.

Attenuation

This is the part where almost writers would whip out the really absurd mathematical formula that lets you calculate attenuation based on frequency, distance, dielectric constant, conductor resistance, foursquare roots, subscripts, greek letters, and cervix pain.  Because of severe mathematics-related childhood trauma, I'm not going to do that.  I'm just going straight to the standards established by ANSI/TIA 568.4.  The maximum supportable distances for broadband coaxial cabling applications are summarized in Tabular array 1.  "Series 6" refers to RG6 coaxial cable and "serial xi" refers to RG11 coaxial cable.

Tabular array one. Maximum support distances for broadband coaxial cabling applications

**Have annotation these distances are inclusive of the patch cables too!  The distances listed are the accented maximum immune from powered device to powered device.  Known otherwise as the "aqueduct".

Remember that these are maximum values due to attenuation from the loftier frequencies of broadband signals and the blueprint of the cables.  Those are non the only factors that contribute to betoken loss.  In fact, just virtually everything you exercise to make coaxial cablevision useful adds even more to the total attenuation, further shortening the useful length of the cablevision.  Every connector, splitter, and wall outlet adds to the total attenuation.

Insertion Loss

Insertion loss is really merely what information technology sounds similar.  It'southward the point "loss" that happens as a result of "inserting" annihilation into the betoken pathway.  By "anything" I hateful things similar electronic devices, hardware, splices, ...anything.

One of the biggest producers of insertion loss in a coax bespeak pathway is a splitter .  A splitter is a device that splits the betoken into two (or more) signals so that it tin can feed two devices, like when ane antenna is shared between two TVs.  This necessarily results in a large amount of point loss, as each of those TVs are at present just going to receive 50% of the signal it would have gotten if it had the antenna all to itself.  Figure 1 shows how the splitter produces a signal loss of fifty%.   Signal strength (and signal loss) is expressed in units of decibels.  Since we're still fugitive PMSD (post mathematics stress disorder), Effigy ane  also helps u.s. to sympathise the decibel.  After all the math is done, by somebody somewhere, information technology turns out that a 50% loss of indicate force is most equal to a loss of iii.v dB.

Figure 1. Attenuation (signal loss) due to apply of 1 splitter

That'south only for one splitter.  Many homes have more than ii TVs,  some homes accept quite a few TVs, and that means more splitters.  As shown in Effigy 2, addition of some other splitter to the point path doubles the attenuation to 7.0 dB, and cuts the signal strength in half over again.  So afterwards the addition of the second splitter, we're down to just 25% of the original signal strength.

All of those figures are for hypothetical splitters that operate at 100% efficiency which, of course, nothing actually does.  Also, each cable connexion adds more than attenuation due to signal leakage.  These pocket-size signal losses are usually less than half a decibel, but they add up.  Especially when you start including union fittings, wall outlets, a cable from the wall outlet to the fix pinnacle box, the fix top box itself, then a cable from the cable box to the TV.  And so as a dominion of pollex, most installers expect each splitter to add betwixt 3.6 dB and four.0 dB to the full attenuation.

Figure two.  Attenuation (signal loss) due to utilise of ii splitters

When coaxial cable is used to provide a dwelling house with both broadband net and television service, the installer will ordinarily road 1 of the outputs from the offset splitter to the cable internet modem, and so use the other output to separate further for multiple TVs.  Yous tin can come across why in Effigy 2.  This arrangement provides the strongest signal to the internet modem, which is where most users need the greatest bandwidth.

More on Attenuation

At present that we understand a little bit nigh decibels from looking at the event of splitting the point in half, we tin talk a little chip more well-nigh attenuation of the cablevision.  Remember that a signal loss of 50% is almost equal to -3.five dB and a loss of about -seven.0 dB means that well-nigh 75% of the original signal is lost.  Sticking with the same pattern, does a loss of -10.5 dB  mean that virtually ninety% of the original point is but gone?  I'thou afraid then.

So now allow's talk nearly some existent-life frequencies and real-life distances.  In the olden days of Television, the VHF channels 2-13 operated at frequencies of 54-216 MHz.  Actually, they still do.  When we await at that range of frequencies in Tabular array 2, we tin estimate that the signal loss for those channels is betwixt about 1.v dB and 3.one dB, for a cable length of 100 feet.  That'due south well below the insertion loss from a single splitter, and one can imagine how longer cable distances are possible for VHF Telly channels, particularly for channels ii-5, which e'er seemed to come in best, right?

Table 2.Attenuation Values for RG6 Quad Shield Outdoor Coaxial Cable

Compare that to the betoken frequencies from satellite TV providers, which tin be every bit high as 2150 MHz.  At that frequency, attenuation of just the cablevision is well-nigh 10 dB for that aforementioned 100 feet -- well-nigh 85% of the original signal!  And those are compressed signals.  If we're talking nigh existent 1080p HDTV, the frequency is more like 3000 MHz, and over 100 anxiety of cable, it seems similar there won't be much bespeak left at all.

And then if all you lot need are the soap operas from that old NBC chapter on channel 4, then put your antenna out on the befouled, down the road a piece, or even share it with your neighbors.  But for today'due south broadband cable Net and television applications, keep your cable runs short, and the fewer splitters, the better.

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