Communications: Voice, Radio and Data - Problem relocating cable modem

I have a problem that is driving me crazy. I'm relocating my cable modem from the computer desk to the closet where the structured wiring cabinet is located. The modem won't sync and connect when moved, and I can't for the life of me figure out what's wrong.

Here's the setup that is working fine: Comcast coax runs from outside into the closet. Female/female adapter on the end of that. Coax to computer desk attaches here, and ends in a keystone wallplate at the computer desk. Coax patch cable runs from wall jack to cable modem, and all is well (modem syncs and goes ready).

If I move the cable modem into the closet and connect it directly to the Comcast coax, the RECV light flashes constantly and the modem never goes ready. If I put a patch cable between the cable modem and the Comcast coax, same problem.

So this leads me to believe that there is something "special" about the coax that runs from the closet to the wall jack at the computer desk, since this is basically all that is changed from the working arrangement. But I can't see anything unique about this run at either end or for as far as I can visually trace this cable until it disappears into walls.

I'm really puzzled that the modem doesn't go ready when attached directly to the Comcast feed. Anyway, I'm where I can't see the forest for the trees now. Probably a simple answer and I'll feel real stupid, but I'm ready to accept that now and move on with my project.

Thanks for any advice!

Jim

I would suggest a service call to your cable company.
In all scenarios, it should work when connected directly to their feed. While it's a stretch (and I don't know that much about cable service specifics), it may be possible that your direct connection is somehow overpowering, and the extra cable length and connectors are just enough resistance to drop it into something the modem can use.

The cable tech will attach a device to cable and take all the readings he will need to find out if this is the case.

Going along with Pendragon's theory ... Try adding a splitter (5meg-900meg or 5 meg-1gig) or two in the closet. Each two-way will knock the signal down 3dB which would be the same as adding a long length of RG6.

Thanks for the info, Rick and Pendragon. I had both a -3.5dB and -7dB splitter available, so I started with each, and then in tandem (-10.5dB total?). Still no joy; RECV light still flashes with no eventual connection.

I can probably find a couple more splitters if you think I need to keep adding insertion loss until I hit the magic number, or maybe it's time to call the cable guys and go work on something on my list that I can handle. :)

Thanks!

Follow-on to the diagnostics: I took the cable modem outside and hooked it up to the provider's line at the ground block. It works fine there (syncs and connects).

So this just adds to my confusion. Signal is okay at the ground block. On the home run from the ground block to the wiring closet, it will not work there. Connect this HSD input to the cable run to the computer desk, and once again it works at the desk. Can you say "huh??"

I also tried to connect via other unused coax runs to other rooms, and none of those worked (modem never syncs up). Is this suggestive that maybe there is some sort of amplification going on in that one run that works? I've looked at that cable run everywhere it is exposed and can not find any in-line device. I would think it pretty unlikely that there is something attached in the hidden paths within the walls, right?

So, don't know if this new information helps or not. Wonder if it would be worthwhile to run down to Radio Shack and pick up a $33 bidirectional amplifier?

Thanks!

Problem Solved!

It was a stupid cable labeling issue! Except for the possibility that someone might learn to not take installer-labeling for gospel, I wish we could delete this thread so someone doesn't follow it thinking there is some highly technical situation.

The cable co. installers put beautiful tags on the ends of the cables in the wiring closet. They just had the stupid things backwards. So when I thought I was tapping into the cable from the ground block, I was just attaching to the dead cable running to the computer desk. Sheeessshhh!!

Thanks for all your help Pendragon and Rick, and I'm sorry I didn't start with just the most simple basic step of validating the physical layer (note to self - quit rolling eyes when tech support asks "Is it plugged in?" :) ).

Red-faced Jim