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if i were to put a splitter on the cable that comes into my room send 1 to my hd dvr the other to the other room would it be ilegal aka stealing cable would it degrade the pic on the hd dvr ?
 

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Not illegal.

As for potential degradation? That depends on the incoming signal strength, quality of the cables/connectors and length of cable run(s).


Typically, it should be no problem at all.
 

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Also be aware that the one going to the other room if plugged diretly into a TV will have a very limited number of channels.
 

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Not illegal, however, if your CATV provider has gone all digital, you'll likely need a set top box ..
 

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a "settop box" may be worthwhile if HD outputs or DVR function are useful.


what may be minimally necessary is to tell your friendly cable provider to provide the requisite multiple free DTAs @ $0.00 (zero point zero zero) per month. 2 or 3 DTAs depending on whether you have one rented settop box already.


each DTA is for use with splitters and any old analog/NTSC tv/vcr.


also regarding the question of degradation of the picture - answer is no degradation unless its too much power/dB drop, in which case massive pixellation & freezing/disappearing of picture will occur. also tuning between channels might get slower as you near edge of acceptable signal power ; each split reduces power a tad, mostly/only on the downstream side of the split.
 

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Quote:
Originally Posted by tveli /forum/post/0



also regarding the question of degradation of the picture - answer is no degradation unless its too much power/dB drop, in which case massive pixellation & freezing/disappearing of picture will occur. also tuning between channels might get slower as you near edge of acceptable signal power ; each split reduces power a tad, mostly/only on the downstream side of the split.

A couple things I am not sure I agree with.


I'm assuming you meant that pixelation will occur when there is too little signal. Although it can occur with too much, this probably wouldn't pertain to the OP as he is splitting the cable, not adding an amp. Pixelation is also not always massive, as it can be just enough to drive you nuts but still be able to watch.


I also can't say I've ever witnessed slow down in tuning due to signal levels that are even borderline acceptable. It's usually slower no matter what, than analog tuning. Not saying it can't happen as in theory it makes sense, just that I've never seen signal levels affect tuning speed unless signal was totally shot and even then it's more that it cant the the channel rather than it is slow to tune.


Each split will reduce the signal by at least 3.5 dB, and a bit more on the higher frequencies. A splitter WILL definitely affect both the downstream AND the upstream. Again each split WILL reduce the downstream AND increase the upstream levels by around 3.5, so be aware if your cable Internet modem is going to be affected by this extra split as it would be more sensitive to upstream levels. Meaning if the cable modem will be on or after this new splitter.


As said before, you should be ok splitting, but it all depends on what you have coming into the house and how many other splitters you have already. And I can't stress enough how poor connectors or wire can cause problems. Unless you have the wire and the tools, it would probably be cheaper and less likely to be problematic, to have the cable company do it for you. That way they can address any signal issues if they arise.
 

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Quote:
Originally Posted by Weags /forum/post/20805225


... AND increase the upstream levels by around 3.5.

I'd double check on that. The splitter is passive. Upsteam levels from each device (I.E. STB and modem) will be unaffected.
 

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Quote:
Originally Posted by Ratman /forum/post/0



I'd double check on that. The splitter is passive. Upsteam levels from each device (I.E. STB and modem) will be unaffected.

Maybe I misworded it. But with just about any run of the mill splitter, the transmit (or as I referred to it as upstream levels) will increase. So if his modem has a TX of 50 now and he adds a two way splitter, it will increase to 53.5.


PS. A passive splitter only means it does not need a power supply. It qualifying as a passive device does not indicate it's affect on signal upstream or downstream.
 

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I don't know... I have to question that logic.


Here's my thought. I agree the downstream signal power is halved (-3.5dB), that's common knowledge. One in... two out.


How can the upstream power be doubled? No matter which side is being fed upstream, it's two in, one out. BUT, the A feed will still be 50 and the B feed will be 50. Essentially each feed (going upstream) is an independant signal and level sharing one outboound pipe. A one to one relationship.


If your statement were true, if someone needed a "power/signal boost", why not just use a 2-way spliiter (or a 4-way for +7dB) in reverse instead of buying an amp?


And I know the difference between active and passive.
 

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Quote:
Originally Posted by Ratman /forum/post/0


I don't know... I have to question that logic.


Here's my thought. I agree the downstream signal power is halved (-3.5dB), that's common knowledge. One in... two out.


How can the upstream power be doubled? No matter which side is being fed upstream, it's two in, one out. BUT, the A feed will still be 50 and the B feed will be 50. Essentially each feed (going upstream) is an independant signal and level sharing one outboound pipe. A one to one relationship.


If your statement were true, if someone needed a "power/signal boost", why not just use a 2-way spliiter (or a 4-way for +7dB) in reverse instead of buying an amp?


And I know the difference between active and passive.

I think you are misinterpreting what is said. Raising a TX isn't "boosting" it at all. Basically a 53 tx is worse than a 50 TX. Pretty much the TX is affected by what is between the modem and the head end. Any time you put a splitter in between it raises the TX. I am not going to debatee the logic or the scientific explanation of it, but that's how it works.


A quick test you could do is bypass one splitter in your home and check your modem diagnostics page. The upstream or TX will change(lower) depending on the value of your splitter and will do so by roughly the same amount of loss that splitter has taken away from the downstream. Put the splitter back in and it will increase again. Again this is how it works and has been this way for at least the 10+ years I have been working with them.


I also do not question your awareness of the difference between passive and active, but saying a splitter won't lose signal on the upstream because it is passive has no actual correlation.


This is not MY theory. It is the real world application of a splitter in relation to a cable modem or similar devices transmit levels.


As far as reversing a splitter to gain signal it just doesn't work that way. If you reverse a 2 way one tv would be snowy and the other would be fine.


I don't pretend to know How or why splitters work like they do. I just know from field experience how it affects signal levels both forward and reverse. whatever a modem has to receive signal through, it also has to send back through.


I hope I've managed to explain it as sometimes my thoughts don't come out as clearly in words but I am 100% certain upstream or TX levels increase with every splitter added. I work with them every day for a living.
 

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However you want to justify it.


Here's what I have always understood:

A passive splitter cannot "increase" the signal on the return path. The same as that you cannot use a splitter in reverse (as a combiner) to gain signal.


If you could provide some technical reference to substantiate your statement(s) would be appreciated (and shut me up).



OTOH, if you simply mean that a "cable modem" automatically compensates it's TX levels based on RX levels, that's entirely a different subject and nothing (per se) to do with a splitter.


Anyway... most cableco's will install the cable modem (if possible and as recommended) after the "first split" when it enters the premises.
 

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Quote:
Originally Posted by Ratman /forum/post/0


However you want to justify it.


Here's what I have always understood:

A passive splitter cannot "increase" the signal on the return path. The same as that you cannot use a splitter in reverse (as a combiner) to gain signal.


If you could provide some technical reference to substantiate your statement(s) would be appreciated (and shut me up).



OTOH, if you simply mean that a "cable modem" automatically compensates it's TX levels based on RX levels, that's entirely a different subject and nothing (per se) to do with a splitter.


Anyway... most cableco's will install the cable modem (if possible and as recommended) after the "first split" when it enters the premises.

I think you are looking at it the wrong way. I guess how I should say it is that a splitter accounts for return loss, but when you lose on the return the number gets higher. I don't know how to explain it otherwise. The splitter is causing a loss of signal but the measurement number increases. Meaning if a modem is at receiving at +5 and TX and 50 and you add a 2 way splitter in line ,the modem will now be at +1.5 and TX at 53.5. I'm telling ya man, this is how it works. Trust me.



Your use of passive when it comes to splitters ONLY has to do with it's ability to function without a power supply. It does not mean that it is passive in the sense that it lets signal through back and forth unimpeded.


Most cable companies install the modem on the first leg of the splitter so that it gets the straightest shot and has less potential for high TX issues. It is always easy to raise a TX number by adding splitters or attenuators whereas you cannot lower it without removing splitters or having plant redesigned.


Ok and here's my last ditch effort to shut you up. It's the first thing I found and it seems to explain return loss when it comes to splitters. It's not the most technical explanation but it should suffice...even for you :p


Return Loss (dB):

Every time you put a splitter or amplifier into your cable line, it causes the signals going BACK to the Cable Company to weaken. This is particularly problematic if you are using a cable modem or Digital Cable Services. If the signal that the cable modem or Digital Converter sends back to the Cable Company is too weak, your services may not work. Each splitter or amplifier is rated for (return) loss, which basically tells you how much signal strength you lose when the signal goes back through the splitter or amplifier. Here are some approximate Return Loss numbers for common situations:


TABLE 4


Splitter Type dB Loss % Signal Strength Lost

2-port 3.5 56%

3-port 5.5 72%

4-port 7 80%

8-port 11 92%

These numbers are all based on HIGH QUALITY 1 GHZ splitters. Lower quality splitters will likely have higher loss numbers. What about the Amplifiers? Amplifiers also cause return path signal loss. Those numbers are listed in Table 3. Bottom line, this means that even if you use an amplifier, you could end up with weak signals going BACK to the Cable Company. That's why the cable company usually uses a dedicated cable line for your cable modem, so that the signals traveling back to the cable company stay as strong as possible.
 

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Quote:
Originally Posted by Ratman /forum/post/0



OTOH, if you simply mean that a "cable modem" automatically compensates it's TX levels based on RX levels, that's entirely a different subject and nothing (per se) to do with a splitter.

A cable Modem TX has very little to do with the RX. Both numbers will vary widely depending on location, plant design and wiring configuration amongst other things. I remember not too long ago having a lengthy "discussion" on here with an "old cable dawg" who was convinced he could tell someones TX at a modem using only the RX levels. And I still stand by the fact that the two levels have little if anything to do with one another. It would be like saying that because your modem RX is at +1 then your TX has to be 42.I could pull up 1000 modems to prove thus wrong.


The modem only knows the specs it needs to work properly and doesn't compensate for one or the other based on one or the other.
 

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LOL...

I give up. I do not agree with any part of your explanation(s) or justfication(s) and how that references how passive splitters add/increase power/signal on the TX/return/upstream. Although... all of the "return loss" stuff that you cut and pasted is accurate. And I'll leave it at that and shut up. Sorry, but you're are either confused or can't properly relate the technical facts to back up your statement in post #6
Quote:
...AND increase the upstream levels by around 3.5, so be aware if your cable Internet modem is going to be affected by this extra split as it would be more sensitive to upstream levels.

To the OP:

Refer to post #2
 

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Guys

This is the reason: the upstream transmit power is determined by the attenuation between the cable modem or STB and the CMTS, so if you increase the attenuation in that path the cable modem has to work harder to overcome the additional attenuation.

So adding another 2 way in line adds the 3.5db attenuation.

The modem will increase its upstream power from 50 to 53.5dbmv.


Typically the CMTS wants to receive the upstream frequency at 0dbmv, so it tells the modem or STB how much power it needs to put out to reach it at the desired level.
 

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Quote:
Originally Posted by RCbridge /forum/post/0


Guys

This is the reason: the upstream transmit power is determined by the attenuation between the cable modem or STB and the CMTS, so if you increase the attenuation in that path the cable modem has to work harder to overcome the additional attenuation.

So adding another 2 way in line adds the 3.5db attenuation.

The modem will increase its upstream power from 50 to 53.5dbmv.


Typically the CMTS wants to receive the upstream frequency at 0dbmv, so it tells the modem or STB how much power it needs to put out to reach it at the desired level.

Thank you RCbridge.


I hope this clears it up Ratman so you don't think I'm just making stuff up. May be in different words but is saying the exact same thing :Add a splitter and the TX INCREASES by the value of the splitter.


Anyone familiar with cable modems or cable wiring should know this. It is basic cable 101.


I am not confused and I honestly did not feel that a technical explanation like the very good one RCbridge gave ,should be needed to get this very simple concept of how splitters affect cable modems upstream levels. Especially when it comes to people who are giving others advice about cable wiring. It is what it is. No hard feelings
 

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As I tried to suggest earlier, based on the RX attenuation. the MODEM increases TX power (as alluded to in post 11)... not the splitter. I have been clear since post #7.



Thanks for stepping in to clear up the explanations.
 

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Quote:
Originally Posted by Ratman /forum/post/0


As I tried to suggest earlier, based on the RX attenuation. the MODEM increases TX power (as alluded to in post 11)... not the splitter. I have been clear since post #7.



Thanks for stepping in to clear up the explanations.

Again you are wrong. If I put a cable signal attenuator that reduces signal only the high end frequencies by around say 6db, the TX of the modem will only change by around 1. It is in fact the splitter itself that affects the TX. If I put an amp in with a built in splitter (2 amplified outputs) and increase the RX by say 11.5 it will still increase the TX by 3.5 due to the splitter in the amp.


Spin it however you want but I can play with RX levels and the TX will only change depending on which kind of device I choose to use. It is up to the return loss specs of the device that the TX will change, not the modem.
 

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Uncle... you win with your spin.


I can live with post 15.
 

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- regarding slower channel change with poor signal ; my hodgepodge of cheapo QAM tuner devices have enough trouble with perfect signals - indeed way slower than we were used to with analog tuners.

The local free DTAs are AMAZINGLY FAST at channel changes - fastest QAM channel-change I've ever seen!!!!!!!!! i suppose it's just the latest/greatest cheapo chipset provides that quickness? somebody somewhere wrote some nicely optimized software/gate-arrays/VHDL/whatever. I wonder if the micro-DTAs are measurably slower channel-changing marginal signal levels. Please don't make me test it. (As if I can actually stop myself before I return the DTAs to Comcast.)


- does our squad of uber video nerds agree that especially if there are internet/cable-modem problems, it is generally best to try the cable modem as close to the outside cable - using the least # of splits to the modem?


- no the power level does not double upstream via the splitter itself nor does the upstream signal transit the splitter perfectly/ideally. the cable modem xmit power could theoretically auto-adjust, maybe by talking to headend via whatever protocol, negotiating to bump up (or down) its xmit power by 3 tads. if the connection meets requirements just as well with the power bumped down 3 decibels, and you multiply that by a couple billion customers, that adds up to super green Al Gore gigawatts of power, saving the planet for future children so they can watch cable too.
 
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