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#640155 03/04/21 03:53 AM
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While zipping around the Internet, I came across an article that discusses coaxial cable.

As I read the article, I began to wonder about some of the things stated by the author.

For instance, the author refers to coaxial cable having a copper center conductor. My understanding is that the most commonly used coaxial cable is copper coated steel. Solid copper would be used primarily for satellite installations.

For connectors, twist and crimp connectors are mentioned, but, not compression.

RG11 is mentioned, but, that type of cable wouldn't be common in residential installations.

There are some other things stated that I'm not too sure about.

Here is the link to the article....

click

Is my understanding of coaxial cable not quite right? ponder


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dexman #640161 03/04/21 06:03 PM
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Uggh! One of those consumer articles.

Quote
Is my understanding of coaxial cable not quite right?

Probably better than the person who wrote that piece.

Copper center conductor- coax can be had either way, copper or copper clad steel. Solid copper costs more but you would use it where the cable is used to carry current also, like for a preamp, satellite LNB, switch, etc.

RG-11, we only used that for long drops. The only time we used it in buildings was in the "early days" for large apartment and commercial installations for distribution between closets. After that, when bandwidth increased, we switched to .500 hard line instead. Always had that around.

Compression connectors are the standard. They probably don't mention them because the typical DIY that this article is aimed at wouldn't want to spend the money on tools nor know how to use them. The older hex crimp connectors are OK but are no longer used. They are not water proof for one reason. They had to be used with a boot filled with silicon grease outdoors. Twist-ons should NEVER be used!

What other things aren't you sure about?

Last edited by hbiss; 03/04/21 06:07 PM.

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dexman #640162 03/04/21 07:24 PM
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Hal, Well said......

dexman #640166 03/04/21 09:51 PM
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I read that runs of RG11 that are less than 100' long can run into problems with reflections. RG6 and RG59 are less susceptible to it. I didn't see that addressed in the article. ponder

Unused ports on splitters should be terminated rather than left open

Even though I don't regularly work with coaxial, I think that my compression tool was worth the cost. I've had crimp connectors fall apart. Compression connectors have been rock solid. smile


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dexman #640174 03/04/21 11:21 PM
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I read that runs of RG11 that are less than 100' long can run into problems with reflections. RG6 and RG59 are less susceptible to it.

Micro reflections. Umm, yeah, I've heard that you should avoid using less than 2 foot cables to interconnect equipment. The impedance match isn't perfect and a short cable length can cause the reflections that will occur to interfere with the digital QUAM signal. Supposedly anyway. Never heard anything about what you are saying. Wouldn't make sense.

Yes, unused splitter ports should be terminated. By the same token unused wall plates off those splitters should be terminated too- but they never are.

-Hal


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dexman #640176 03/05/21 02:07 AM
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Here is the article that looks into RG11. The author describes the reflection factor...
RG11_Cable


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dexman #640177 03/05/21 03:31 AM
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(That’s the reason commercial installers like cable lengths to be two feet at the minimum.) However, the bulky RG11 connector and the big thick cable combine to allow reflections to travel up to 50 feet back down the cable. Keep in mind that there’s a reflection on both sides and that’s why it’s a bad idea to have RG11 cables that are shorter than 100 feet.

Yes, 2 feet and I've never seen that to even be a problem. But that stuff about RG-11? I would like to know where he got that from. Why then shouldn't RG-6 not be shorter that like 20 feet? Sounds like there are some "vidiots" (cousins of audiofools) who think that RG-11 would be the ultimate cable to wire their houses with and that's who the article is written for. Like I said, I haven't seen it used in years. No reason to use anything other than RG-6 size cables.

-Hal


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dexman #640185 03/05/21 05:21 PM
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I have a pair of 3-way splitters in use here at home in order to serve three TVs and two WIFI extenders. In one instance, a 2-way splitter is being used to divide a single coax line to support a TV and extender. (Verizon Fios).

I know that splitters attenuate signals. Is there some rule of thumb as to a limit of splitters that can be used on a line before degradation becomes a problem?

I'm using, very roughly, 200' to connect the TVs and extenders.

All cable is Belden 1189A and 1613R.


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dexman #640189 03/05/21 08:40 PM
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The only rule that I ever follow is to never feed a splitter with another splitter.

The signal level will drop real fast. Take a 2-port splitter that has 3.5dB loss per port, one splitter will cut your signal level by half, add a second splitter and the signal is cut by half again. You need up with a signal level that is only a quarter of what you started with.


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dexman #640191 03/05/21 09:13 PM
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No. You have to know how to do a design. First, you have to know what you have to work with then what you need at each cable box.

For the sake of simplicity lets say that you have +10dbm at the ground block (or video output of the FiOS ONT). +10 is what we would normally shoot for to supply each house. Then figure that at each cable box you want between 0dbm and no less than -10dbm. That range is what cable boxes are designed to operate with. We're going to ignore signal "tilt", which is the difference in levels between the lowest and highest carriers, as well as the return signals from the cable boxes back to the system.

So now it's just a matter of simple math.

If you don't know a 2-way splitter has a 3.5db attenuation from the in to each of the outs. A 3-way comes in two varieties. Either symmetrical or with a "hot"port. Either it's -7 all around or there is a -3.5 port with the rest -7. A 4-way is just two 2-ways. So -7db from the in to the outs.

Now look up the specs for the cable you are using. Look for the attenuation at 1000Mhz, for the 1189A it's 6.55db/100ft. It's given per 100ft so divide it down to per foot (.065/ft). Now determine all your individual cable run lengths and where they go.

Get your pencil and paper out and start with +10. Subtract .065 per foot for the length of cable between the ONT and the first splitter. Subtract 3.5 or 7 for the 3-way splitter. Subtract from that number .065/ft for each cable run from the splitter to the cable boxes. Do you end up with between 0 and -10 at each device? If so all good!

Hint- it's a good idea to make a drawing starting at the ONT of how you have your splitters connected along with cable lengths and where they go. That way you can write your levels at each point in the chain.

-Hal


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