Cable Modems and Drop-Amps

Hey all.

I have (had) a drop-amp hooked into my cable modem, but for some reason, the connection to the @Home servers is cut. (IE: no connection) But it works fine if I hook it to a connection that the TV uses. (IE: IMproves the TV reseption)

A buddy of mine got a cable modem and the tech hooked up a Drop-Amp as there was a TV on the same run of cable.

My question: is there a specific type of drop-amp that can be used for cable modem? Or is there just something screwy with the one I have?

A drop amp only amplifies the signal in one direction, the signal going to the television. i.e. downstream. A cable modem requires signal to travel in both directions downstream and upstream. Using a drop amp as I stated above only amplifies the downstream, this amplification interferes with or prevents the upstream signal from reaching the router. It is posible to get a return amp. i.e. does downstream and upstream. Return amps are expensive though and you probably don’t want to spend the money on one.

Your friend probably has the drop amp installed on a line that feeds the television after it the cable has been run through a splitter. Imagine this, wall outlet has a small piece of cable that goes to a splitter the splitter has two pieces of cable coming out of it. One of these cable goes to the amp and then to the television. The second cable goes to his cable modem.

Who installed the drop amp? The cable company or you? Why was it installed?

I used to install cable modems so this is based on my experience. Hopefully this helped. I’ll check back later to see if you need a better answer.

How did I do for my first post?

I installed the Drop Amp. (In the case of my buddy, the cable company did.)

I was mucking about with a TV tuner card I was given.

I managed to get it to work (Although without the audio…but that is an other issue.)

I installed the drop amp that I have here to see if it would clear up teh tv signal. (Yes it is legal, I have a small TV here in my office and just unhooked the TV and hooked it to the tuner card.)

A drop amp wasn’t installed when the cable modem was installed, so I guess it really wasn’t needed. I just wanted to try it out. (I know it won’t ‘increase bandwidth’ ot anything, but it will increase the TV signal.)

So when I noticed the net connectino was down I was thust curious as to why.

If you want to use the TV tuner card and the cable modem at the same time just stick a splitter on the cable and put the drop amp on the leg that leads to the TV tuner card. Using a splitter does drop the cable signal down, generally 3.5dB loss with a two way splitter,so the signal may then be too weak for the cable modem to work. Not likely though. The legality of this depends on how your cable company bills you. Some would want to charge you for an extra outlet.

I can answer more questions if you have them but I think all you wanted to know was why the cable modem would not work with the amp, correct?

I have it split now (sans amp) and everything works fine. But the the DA is placed before the split, the net connection is lost.

In regards to the legality, the connections I am using are sactioned by my local cable company, but my house is 20 years old and when my cable TV was hooked up, the tech was lost, there where splits on splits on splits.

We managed to trace most of them down so I have the connection in the main living room and the two in my office. (The main run comes up into our bedroom and runs into our living room. The tech said they this junction may split into the other bedrooms. He doesn’t know who did all this, but it would be easier to rip the walls out to get it all out…so he left them and said not to worry about them. = )

Yup…that’s about it.

Upon further research and digging around, I found that the newer models of drop amps are the only ones that work with cable-modem connections.

So that, in essence, is the problem. My drop amp is too old.

I feel for that tech and don’t blame him for saying not to worry about them. Happened to me plenty of times.

I didn’t realize newer drop amps would allow return signal. Maybe us Canadians don’t have access to them yet. Nah, it’s more likely I just haven’t kept up with that technology. Anyway glad you found out what the problem was.

This same buddy of mine also used to work for the local cable guys many moons ago…she shuddered when he saw the original hook up. =)

Funny enough, I guess they do. (I to am in Canada, BTW) But I do not think that the local “Radio Scrap” would carry them.

The age of the drop amp isn’t significant, not all new amps are designed for return past-through (although it’s a pretty safe bet that most of the better ones do, especially since pay-per-view services would require it, at least if you can order directly from your cable box).

Another way to clean up your signal would be to try to eliminate all unnecessary splitters on your line. I think terminating unused lines will also help somewhat, although I don’t remember what value of resistor to use (75 ohm, probably).

The Cable Guy and I did this. There are only 3 terminations on the line. We just left the cable in the walls as it was more of a hassle to remove them.

Good point. The DA I have is fairly simple…the $15 jobby.

I just did a quick search like I should have before even answering your OP and found an amp that supports return path.

Looks like you have to go through one of thier sales reps to buy thier products.

Found these guys when I did my initial search.

$90.00 U.S. for the least expensive one.
I’m still looking around for a Canadian distributor.


Just noticed your post. 75 ohm is the correct terminator. Also replacing poor connectors is helpfull.