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View Full Version : inexpensive solutions to low line voltage to a cable modem?


Bires
03-25-2002, 08:41 PM
(This may be informative for those out there thinking of getting a cable modem...) :hmm:

So I finally got my cable modem last February. I was the first in my area to get it. Unfortunately, I live in a townhouse with eight other units on the same node...
Everything was peachy and really fast until a couple of my nieghbors got their modems installed...and mine went bye-bye. The problem is the splitters-if I remove the splitters my workroom (I have two video editting machines, my digital TV reciver, and my cable modem) then the cable works. BTW: The splitters are all rated 3.5db.

So....if I have my line split (between TV and cable modem) then my cable modem doesn't work. I have a technician coming over tomorrow to look at it. If they're cool with my splitting my line three times in the house, they will install an amplifier. If not-they'll say something like "choose between TV and internet in your workroom" (which would stink)

Any ideas on how to boot signal strength to/from the modem so I can have my video machines connected to the TV cable at the same time as the cable internet?
Bires
03-25-2002, 09:37 PM
:hmm: :hmm: In my debugging of the above wierdness, I found that if I plug the cable modem into my switch, and have my computers access the local network looking for a DHCP server, they all access the internet...fast. I thought this was impossible, and required a router.

To sum up: cable modem plugged into switch. Three comps plugged into switch-all accessing the internet.

Is this abnormal? I'm pleasantly confused.
:hmm: :hmm:
i6s1
03-26-2002, 05:06 PM
You may be getting 3 (or more) IP address from your cable company. I get a second one free. Do you have a commercial package or something?
Bires
03-26-2002, 07:22 PM
nothing special that I am aware of...but I do have different IPs-on two different DNS servers-again...weird.
Dave_7
03-26-2002, 08:27 PM
Some of those splitters are of doubious quality... so beware. Some have such low signal-to-noise ratio that they're utterly useless. Or, they are not sensitive to the correct frequency range.

So again... beware.





Dave.
i6s1
03-26-2002, 08:40 PM
Originally posted by Dave_7
Some of those splitters are of doubious quality... so beware. Some have such low signal-to-noise ratio that they're utterly useless. Or, they are not sensitive to the correct frequency range.

So again... beware.





Dave.

beware, also, that the cable company can "see" splitters. They can't see amplifiers.
Bires
03-27-2002, 10:26 AM
beware, also, that the cable company can "see" splitters. They can't see amplifiers.

That's good to know
Legrand[LN]
03-28-2002, 10:27 AM
Originally posted by i6s1


beware, also, that the cable company can "see" splitters. They can't see amplifiers.

How do you know this? Can you point me to technical data?

Thanks...
i6s1
03-28-2002, 01:24 PM
I can't point you to anything online.

Cable equipment is terminated with a resistance of 50 ohms. This is also the characteristic impedence of the co-ax line. If the termination of the line is different then the characteristic impedence, the line will be unbalanced. This results in signals being reflected back along the line. They can go into a neighborhood, and send a noise spike down the line. If they get a signal back, they can tell it is improperly terminated. (They can also tell how far away it is by the time it takes the spike to return.) They can do this right at the box at the side of your house if they felt so inclined.

Amplifiers are designed to have the correct imput impedence. Some splitters may also be designed for 50 ohm imput, but most of them are cheap junk.