F terminator caps reduce loss with oversized splitter? - AVS Forum
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post #1 of 48 Old 06-23-2014, 05:24 AM - Thread Starter
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F terminator caps reduce loss with oversized splitter?

I would search, but the term is too short. If you have say an 8 way splitter and are only using 4 lines, will capping the unused lines basically turn it into a 4 way splitter, or will each line still be seeing the loss as if they were uncapped? I've googled and read both yes and no. I know you should only get the splitter you need, but curious to see if this would work instead of buying a new one anytime you add a line. Thanks.
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post #2 of 48 Old 06-23-2014, 05:37 AM
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No, it is still an 8 way RF splitter even if you terminate 7 outputs and use only 1 output. You have to buy a 4 way RF splitter to lower the splitting losses if you need 4 outputs.
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post #3 of 48 Old 06-23-2014, 05:55 AM
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Agreed with the prior post, but if your signal level is good coming it, then you might be able to get way with the 8-port splitter even though you're only using 4 ports right now.
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post #4 of 48 Old 06-23-2014, 06:03 AM
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I believe a 8 way will have twice the loss of a 4 way even if you are only using 4 of the ports.

Why don't you just buy a 4 way? They are cheap. If you still insist on using that 8 way, be sure to cap the unused outputs with terminating resistors.

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post #5 of 48 Old 06-23-2014, 06:23 AM - Thread Starter
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Thanks. What are acceptable dB losses for each port on a 4 way, 6 way, 8 way etc? I currently have good picture and nothing odd to report from what I can tell, but I'll get a 4 way splitter if it might help. Any recommendations on a good one? Also, if a cable modem is used will this affect internet speeds? Thanks again.
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post #6 of 48 Old 06-23-2014, 06:54 AM - Thread Starter
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One more question. If each port says -7dB, that already takes into account all 8 plugs? So if you buy a 2 way where each port says -7dB and an 8 port where they all say -7dB, is there a difference in the signal strength? Hope that makes sense.
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post #7 of 48 Old 06-23-2014, 07:08 AM
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Quote:
Originally Posted by garface View Post
One more question. If each port says -7dB, that already takes into account all 8 plugs? So if you buy a 2 way where each port says -7dB and an 8 port where they all say -7dB, is there a difference in the signal strength? Hope that makes sense.
A 2-Way loses 3.5 to 4dB per port, 4-Way 7 to 8dB per port and an 8-way 10.5 to 11dB per port. Any thing different printed on your splitter does not make sense. BTW a dB is a dB.
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post #8 of 48 Old 06-23-2014, 07:11 AM - Thread Starter
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Got it, so it's not really about the quality of the splitter, just an "is what it is" type of deal depending on ports. So pretty much any 4 way splitter should be good? I think I have an Antronix at the moment.
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post #9 of 48 Old 06-23-2014, 07:48 AM
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You should already have (or had) a two-way splitter installed by your cable provider. One feed for primary TV and the other feed to the cable modem.

Leave the 2 way splitter in place. That way you shouldn't have any internet problems or signal concerns.

Add a 3 (balanced would be good) or 4 way splitter after the 2-way for the TV feeds.
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post #10 of 48 Old 06-23-2014, 08:35 AM
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F-terms don't affect insertion loss. Their purpose is to eliminate reflections from open ports that otherwise might cause the equivalent of multi-path (echoes) within the cabling system.

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post #11 of 48 Old 06-23-2014, 08:58 AM
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ADTech, you are correct about Terminating Resistors. Most people don't bother to use them.

Ratman, why don't the OP just use a 4 way splitter? I never thought a Cable Modem needed a strong signal. Just asking.

Gar face, I got my splitters from tselectronic.

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post #12 of 48 Old 06-23-2014, 09:23 AM
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Quote:
Originally Posted by Skytrooper View Post
Ratman, why don't the OP just use a 4 way splitter? I never thought a Cable Modem needed a strong signal. Just asking.
Because if the cableco initially installed a 2-way (which they most all do), that's what they'll support when you have a problem.

Also... if incoming signal loss affects a TV, why wouldn't it also affect a modem?

And... It's better to use a 3-way ( or 4-way) splitter than an 8-way.
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post #13 of 48 Old 06-23-2014, 07:00 PM
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Quote:
Originally Posted by Ratman View Post
Because if the cableco initially installed a 2-way (which they most all do), that's what they'll support when you have a problem.

Also... if incoming signal loss affects a TV, why wouldn't it also affect a modem?

And... It's better to use a 3-way ( or 4-way) splitter than an 8-way.
The reason most cable cos use a low value splitter in front of the modem is not necessarily to provide a high forward signal level. They use the low value splitter to keep the return level to one that the modem can generate. I'm fed from a low value end of line tap and my modem works fine through 11dB of splitter losses (return level is 47dB). If I was fed by a tap right at the node or an amp (a 32 tap, usually) the extra loss in the return path would require the modem to produce a 60dB return signal, which is beyond its rated output. FWIW my forward level(s) at the modem are around -9dB at around 575MHz, still well within spec.
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post #14 of 48 Old 06-24-2014, 04:25 AM
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That's fine. OTOH, many folks don't have a clue about "how" cable works.

It's probably a good idea to leave that two-way in place as installed by the cableco. Add all the splitters you want after that point.

Also... it's nice to have two points for diagnosis if/when there are problems. One closest to the demarc and others after the added splitters. Just my opinion.
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post #15 of 48 Old 06-24-2014, 05:06 AM - Thread Starter
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My cable co did not install a two way splitter. The original install had a 3 way for my two tv's and cable modem.
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post #16 of 48 Old 06-24-2014, 06:20 AM
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Quote:
Originally Posted by garface View Post
My cable co did not install a two way splitter. The original install had a 3 way for my two tv's and cable modem.
There are two kinds of three way splitters. One, sometimes called a balanced splitter, divides the signal evenlly into thirds, and the port strengths are typically labeled -5.5dB, and the other, sometimes called an unbalanced splitter, is the electrical equivalent of two, two-way splitters and the ports are labeled -3.5. -7 and -7dB. The cable modem would be connected to the -3.5dB port so it would effectively be connected to a two way splitter.

BTW, several years ago, I measured the signal loss of several eight-way vertical port splitters and the cheap ones typically had losses of about 15 to 16dB. They had three different non-descript and unfamiliar "brand" labels and were similarly shaped as trapezoids with rounded corners. I also checked Blonder Tongue, Channel Master and Antronix vertical port 8-way splitters at that time and the losses of those were all in the expected, 11 to 12dB range.
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post #17 of 48 Old 06-24-2014, 01:11 PM
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Quote:
Originally Posted by AntAltMike View Post
There are two kinds of three way splitters. One, sometimes called a balanced splitter, divides the signal evenlly into thirds, and the port strengths are typically labeled -5.5dB, and the other, sometimes called an unbalanced splitter, is the electrical equivalent of two, two-way splitters and the ports are labeled -3.5. -7 and -7dB. The cable modem would be connected to the -3.5dB port so it would effectively be connected to a two way splitter.

BTW, several years ago, I measured the signal loss of several eight-way vertical port splitters and the cheap ones typically had losses of about 15 to 16dB. They had three different non-descript and unfamiliar "brand" labels and were similarly shaped as trapezoids with rounded corners. I also checked Blonder Tongue, Channel Master and Antronix vertical port 8-way splitters at that time and the losses of those were all in the expected, 11 to 12dB range.

Splitter loss is a function of signal frequency. The 3.3-3.5 dB insertion loss of a 2-way splitter is MINIMUM at low frequencies. At frequencies of 1Gz or higher, loss could be in the 10dB range. MoCA users beware!
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post #18 of 48 Old 06-24-2014, 01:36 PM
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Originally Posted by domino92024 View Post
Splitter loss is a function of signal frequency. The 3.3-3.5 dB insertion loss of a 2-way splitter is MINIMUM at low frequencies. At frequencies of 1Gz or higher, loss could be in the 10dB range. MoCA users beware!
Splitter "loss" is a result of halving the power (with a 2-way). It's not based on "frequency".

Coax cable has the same problems at 1 GHz and lower. Should we not use coax cable?

Any cableco's using frequencies above 1GHz?

Last edited by Ratman; 06-24-2014 at 01:39 PM.
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post #19 of 48 Old 06-24-2014, 01:48 PM
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Originally Posted by domino92024 View Post
Splitter loss is a function of signal frequency. The 3.3-3.5 dB insertion loss of a 2-way splitter is MINIMUM at low frequencies. At frequencies of 1Gz or higher, loss could be in the 10dB range. MoCA users beware!
I doubt that any professional satellite installer would ever use cable TV splitters in a satellite L band distribution system, but the concern with MoCA distribution design is that it has to support what I will call "lateral" signal travel between output ports on a splitter. The output-to-output signal path on conventional splitters has long been considered an invalid path for analog distribution since, not only is it typically over 20dB on even a two-way splitter, it is not flat across the channel and it makes analog pictures look like hell, even when the measured carrier dB strengths are within spec.

MoCA splitters have been designed with uncommonly LOW output-to-output port isolation or loss values for signals in the "ultraband" that send decoded signals from one box to another.

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post #20 of 48 Old 06-24-2014, 02:07 PM
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Quote:
Originally Posted by Ratman View Post
Splitter "loss" is a result of halving the power (with a 2-way). It's not based on "frequency".

Coax cable has the same problems at 1 GHz and lower. Should we not use coax cable?

Any cableco's using frequencies above 1GHz?

ALL current MoCA is 1.1GHz to 1.5GHz. Special MoCA compliant splitters are readily available. Installers should use new, short runs of RG-6, avoid sharp bends, or even consider RG-11.


And yes, splitter loss is indeed higher at higher frequencies, believe it or not.
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post #21 of 48 Old 06-24-2014, 02:50 PM
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Originally Posted by domino92024 View Post
ALL current MoCA is 1.1GHz to 1.5GHz. Special MoCA compliant splitters are readily available. Installers should use new, short runs of RG-6, avoid sharp bends, or even consider RG-11.


And yes, splitter loss is indeed higher at higher frequencies, believe it or not.
Good to know... hope your info helps the OP. Short runs of RG6? What's "short"? Less than 150'... 100'... 10'???

RG11? If anyone has a problem with "short bends" using RG6, how does RG11 make those bends easier?

Have you ever worked with RG11?

And splitter and/or coax cable "loss" does differ with frequency and cable type, splitter type and distance and how it's run and quality of the splitter/cable.... etc.. Loss can happen at lower frequencies than 1GHz also. No argument there.

Do you work for a cable provider?

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post #22 of 48 Old 06-25-2014, 05:02 AM
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Yes, splitters halve (or fourth or whatever) the power (that's why in the commercial satellite world they're called power dividers), but their loss is frequency related in that the higher the frequency the greater the insertion loss. Not drastic, but it is not flat across its bandwidth.

CIAO!

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post #23 of 48 Old 06-25-2014, 05:50 AM
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And yes, splitter loss is indeed higher at higher frequencies, believe it or not.


We believe it, but it's not a function of frequency, as you incorrectly stated.
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post #24 of 48 Old 06-25-2014, 01:03 PM
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We believe it, but it's not a function of frequency, as you incorrectly stated.

Splitter loss is greater at higher frequencies, but it's not a function of frequency. Hmm...OK.
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post #25 of 48 Old 06-25-2014, 01:30 PM
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LOL! Let the games begin!
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post #26 of 48 Old 06-25-2014, 01:55 PM
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It's a function of the device's efficiency (or lack thereof) as frequency increases.

Here's a plot of an Ideal 1GHz splitter and one of an Ideal 2.4 GHz splitter, both available at Home Depot:



Attached Images
File Type: png IDEAL85-132.png (20.1 KB, 88 views)
File Type: png IDEAL85-332.png (21.1 KB, 86 views)
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post #27 of 48 Old 06-25-2014, 03:32 PM
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Jeez...so much for the OP's basic question of 4 and 8 way splitters...LOL!
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post #28 of 48 Old 06-25-2014, 10:17 PM
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Originally Posted by ADTech View Post
It's a function of the device's efficiency (or lack thereof) as frequency increases.

Gee, so it IS frequency related.
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post #29 of 48 Old 06-26-2014, 05:47 AM
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Originally Posted by domino92024 View Post
Gee, so it IS frequency related.
It's also temperature related. but not a function of temperature, nor is it a function of frequency.
I'm guessing it's too complicated for you to grasp, so lets just say yes, you're right, you have a perfect understanding of RF circuits.
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post #30 of 48 Old 06-26-2014, 07:45 AM
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Originally Posted by bac522 View Post
Jeez...so much for the OP's basic question of 4 and 8 way splitters...LOL!
Don't worry, there's a method to my madness! I'll update this a bit later on today with some different plots that do illustrate the specific question originally asked.

Okay, here are four consecutive plots, all done with an Ideal 85-334 four port splitter rated 2.4GHz. Each consecutive plot is for zero, one, two, and three ports terminated. Port #1 of the NA was attached to the "IN" port of the splitter, Port #2 of the NA was connected to one of the outputs.










The biggest change is evident in the top trace which measures S11 - Return Loss. Most folks are more familiar with VSWR which is a different way of representing the same effect. As can be seen, S11 varies by as much as 10-20 dB depending on how the splitter is terminated (or not).
Attached Images
File Type: png 85-334_0.png (17.5 KB, 61 views)
File Type: png 85-334_1.png (17.6 KB, 61 views)
File Type: png 85-334_2.png (17.7 KB, 59 views)
File Type: png 85-334_3.png (17.6 KB, 59 views)

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Last edited by ADTech; 06-26-2014 at 11:49 AM.
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