Amplifying coax signal

[farscapesg1]

OK, finally got my new DualTV cards in along with all my parts for a new media server. Now it is time to connect them up and and get the system running, but the problem is I want it in the office, not the living room.

Currently, this is the way the coax is set up in the house...

It comes into the house and is immediately split with a 3-way splitter. One line goes to the living room (Cable A), one to the office which is connected to the cable modem (Cable B ), and one to the bedroom which isn't used (Cable C).

Due to signal quality issues, I had a friend of a friend, who works for a cable company, come out and check the lines. After running a new line from the termination box to the house, the signal was still kinda weak, so we put an amplifier on Cable A (between the splitter and the jack in the living room). This line is then split with a 4-way splitter and I have been very happy with the signal quality since then.

So, I split the cable in the office with a 4-way splitter (Cable modem, 2 lines for my HDHomeRun, and one DualTV) to test it, and the signal is weak like the living room was before putting the amp on. However, everything I read about coax amplifiers say not to connect it to the line with a cable modem. I guess I could run a seperate coax cable to the office, but I would prefer not to

Is it actually safe to connect a cable modem to a line that is amplified? Are the companies just trying to cover their tails? Should I put the amp before the initial 3-way splitter, or after that split but before it reaches the office? I'm thinking I will need to use a 2-way splitter and send one cable to the cable modem, then split the other cable with a 4-way splitter to get connections for my two DualTVs and two connections for the HDHomeRun. My understanding is that it is best to put an amp before the split so you can amplifying the cleaner signal instead of amplifying signal noise.

Any advice? Should I just suck it up and run another RG6 cable to keep the cable modem on it's own line?

 

[disc]

The problem is a CATV amplifier is not built to amplify (or possible even pass) the higher frequency signals that the cable modem uses. It could, in effect, filter out the modem data. You can certainly try it with little risk involved, but if your internet stops working, it is most likely because the amplifier is preventing data transmission.

 

[Trepidati0n]

1. Connecting cable modem to an amplifier is fine. It takes pretty big signal to whack a modem.

2. However, If you want to do it "right", I would recommend getting something like a Leviton bi-directional amplifier (they have the needed bandwidth capabilities). Might cost you $150 or so, but you will get 10 channels that are amplified and it will support bi-directional communications. I've installed a few of these for friends and family and nobody has been against it after they saw the results.

3. Splitters in general are just bad because what you are doing is effectively reducing the signal by 1/2 for every doubling of loads. If the signal is already poor coming in..splitting it will only make it worse.

Hope this helped.

 

[valve1138]

1. Connecting cable modem to an amplifier is fine. It takes pretty big signal to whack a modem.

2. However, If you want to do it "right", I would recommend getting something like a Leviton bi-directional amplifier (they have the needed bandwidth capabilities). Might cost you $150 or so, but you will get 10 channels that are amplified and it will support bi-directional communications. I've installed a few of these for friends and family and nobody has been against it after they saw the results.

A cable modem won't work behind an amp that isn't bi-directional.

 

[farscapesg1]

Unfortunately, cost is a big factor at the moment. The wife is perfectly happy with the current setup, it's just that I need to get the office line running at the same quality to so everything can be setup before hand and make the cross-over to the new media server as seemless as possible. Considering the amp I'm already using (from the cable company)seems to work great, this will probably be a temporary unit. Even if it was used as a permanent solution, I doubt I could ever get the wife to agree to spending over $50 when she knows the current one is working fine with the current setup.

I would just set everything up without an amp, but I've currently got the line to the cable modem split 3 ways, the cable modem and two lines to the HDHomeRun (which is being used with the current setup). When I switched the 3-way splitter with a 4-way to get one DualTV working, my signal strength dropped on the HDHomeRun, causing some signal issues with recording.

 

[Trepidati0n]

A cable modem won't work behind an amp that isn't bi-directional.

Where did I say it would? His question was more to the point of would the amplifier damage the cable modem. From his post:

Is it actually safe to connect a cable modem to a line that is amplified?

I believe I stated that you needed a bi-directional amp in my second point.

 

[farscapesg1]

Thanks for the advice. I'm really trying to avoid running a new coax cable simply because I don't expect us to be in the same house within a year, and I don't want to put the time, energy, or money (buying enough coax cable to make a new run, plus some of the splitters and amp that I will probably need anyways).

I will try out a different amp tonight, and replace the original 3-way splitter in the attic with a 2-way since I don't use the bedroom line.

 

[EvilSpock]

Before you spend any money - have the cable company come out and check the signal. Home amplifiers create noise which is bad. Cable modems on the downstream signal perform best in the range of -10 to 0dbmv (550 MHz to 870 MHz - digital qam) and transmit upstream signals back at around 49dbmv (5 MHz to 40 MHz). If the cable company is using qam 256 for digital - noise is very bad no matter how much signal is there. Qam256 is used by cable systems that run a tight maintained system and are DOCSIS2.0 capable. On the splitter be sure that the freq range is 5 MHz to 1000 MHz. You pay good money to the cable company each month have them check and tell you the signal and noise ratios you are getting at the side of your house - Start Here First before doing anything else- . The signal at the side of your house should be at least 7dbmv @ 54 MHz and 10 to 15dbmv at 750 MHz. Then get your cable back to where the cable enters the house then split it based on what you have hooked up in the house - 2 TVs and a cable modem = 3 way or 4 way splitter.

 

[farscapesg1]

OK, after some further investigation, a amp isn't going to do me any good, because I already have one. After crawling around in the attic and tracing out the cables, I found that the amp that was installed alread is a bi-directional one that is attached to the cable as soon as it comes in, and amplifies every line in the house. After the amp it went to a 2-way splitter, with 1 cable going to the office (cable modem), the other cable was split again and then fed to the living room and bedroom.

So, I've taken out the extra splitter so now it is just split once, going to the office and the living room. Then the signal is split in the office with a 5-1000 4-way, going to the cable modem, two cables for the HDHomeRun, and finally to another 2-way which feeds the two DualTV tuners.

Signal quality seems better, but now I think my problem is cables and the fact I had to use a 5-900 two way instead of a 5-1000 digital (maybe...or it may just be because it was a cheap RCA brand 2-way). Picture quality is almost there and is affected by how tight I make the cable connections or how the cable is pulled against the connection in one directin or another, so I'm sure once I replace the cables and the 2-way I should have a signal comparable to the living room setup (where my current HTPC is).

I am using mostly hand-made RG6 cables with twist-on connections. I'm going to return the amp and some extra splitters I thought I might need and pick up some pre-made cables (with compression F connectors) and a better 2-way.

At least that explains why putting another amp (even a cheap one) on the line made the picture so much worse I was amplifying an already amplified signal.