cable amplifiers and adding more splitters to the cable/internet main line.?

Question

A crude visual description of my current setup:

MAIN LINE (split) ->
-digital receiver into gramps house.
-internet line into my house.
INTERNET LINE (split) ->
-line to cable modem.
-line to tv.

My question: can I split the line to tv so that it runs to another tv without quality degridation (mainly the internet)? Or will I need to buy an amplifier, and will the amplifier even help?

extra info: the two splitters I have now are 5-1000mhz and 3.5db at each prong. the cable modem receiver signal strength is ~ -9.0dbmV and the signal is acquired at 705mhz.

I can post more info if needed. Thanks!

the SNR is ~37.7db

Regarding your ascii diagram: I purchased an amp with the intention of using it exactly where you indicated. It's a bi-directional amp that claims to raise signal by 10db. Radioshack also sells a 4-way split bi-directional amp which claims to raise signal by 8db. Should I get the 4-way amp instead and put it behind the modem, would that (a) be ok for the internet connection, and (b) get the internet line away from "almost bottoming out" status?

Answer 1

Your modem is already about to bottom out (what's your incoming SNR?), so make sure you leave that leg of the second splitter alone. However, you can split the line going to the TV as many times as you want, but the signal will degrade. I suggest you do the following:
`````````````Main`````````````
```````,_____|_____,````
``````you``````````grandpa`
````````|```````````````````````
````````2-way split```````````
````````,____|_____,``````````
```modem````````amplifier```
```````````````````````|`````````
```````````````````2-way``````
````````````````````,_|_,````````
`````````````````TV`````TV````
Just don't amp the modem unless you have a Forward/Return amp and your SNR is already above 33.

Ideally, analog TV should be above -15dbMV, and cable modems should be between 5 and -5 dbMV with an SNR above 31.

Edit: Depending on what cable company services you, they'd very likely provide an amp for you at no cost if a technician believed you needed it. Honestly, we run into a lot of trouble with Radio Shack amps, and even our high-quality Antronics amplifiers have to be used carefully inline with a modem. I suggest you first pop the amplifier you currently have into the system before the modem and see if it works. Pay close attention to the return signal, it should be below 53 (and as always, keep an eye on the SNR). If it works, great. There's really no reason to buy a 4-way amplifier... they're an elegant-looking solution, but electronically speaking, they're a slightly stronger amplifier with a built-in splitter. I rarely use them. If it doesn't work, just keep the setup you have and amp the TVs-- if your SNR is that high, and your return is below 53dB, you're in great shape.

Answer 2

yes, you can. signal to the modem should not be effected, but on the tv side you might start to notice some channels will start to loose quality, amount of channels and quality will also be determined by type of cable. as for the amplifier, yes it will help, but don't put it inline with the modem.