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Old 03-23-2008, 06:03 PM   #1
Dessert Tears
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Default Cable Internet connection out, TV fine; Weak signal

I live in an apartment building with poor cable wiring: for certain apartments, the cable is routed through other apartments. For example, the wall box in my apartment has 3 wires: incoming cable, a bypass, and the bypass return. I connect the incoming cable to the bypass with a coupler and use the return; disconnecting the bypass disconnects other apartment(s). My incoming cable line comes from another apartment.

My cable Internet connection has been out for a week. A few TV channels have been affected (corrupted ? completely gray, OK ? corrupted), but the TV is generally fine. At the original onset, it was out 1 day, working 1 day, then out. The Time Warner Cable follow-up technician tested the incoming line and found that it had weak signal. He explained that only a portion of the signal was completely attenuated, which is why the TV continued to work. The tech said that the likely cause was a wiring or equipment issue in an apartment and that the solution would be to get a TWC tech into that apartment.

The tenants of an apartment connected through my apartment are seeing similar problems. At present, we have been unable to contact the tenants of the likely apartments. Furthermore, we anticipate difficulty in scheduling a service call at their convenience.

Hypothesis: The tenant is using a 1?3 (2 TV, 1 modem) splitter, connecting the bypass to one of the TV outputs.
  • The tenant would receive better signal by connecting ahead of the bypass.
  • The failure mode (connected, but weak signal) is inconsistent with a tech ignorant of the building. The techs do make mistakes ? my installing tech disconnected the apartment(s) dependent on my bypass ? but I've only heard of outright disconnections.
  • It is unlikely that the tenant could have scheduled TWC service calls to match the 1 day down, 1 day up, continuously down pattern.
  • I assume that all connections are made properly.
  • I assume that there is some sort of filter in the splitter. Is this correct?
Is my hypothesis consistent with information I provided? Is it likely, or are there many plausible causes?

I know that the best and only real answer is to get a TWC technician into the apartment. In the interim, would a "cable booster" be likely to help? As we have had general signal strength issues, we would continue to use it after the resolution of this particular issue, and we would be willing to spend around $200.

Cliffs
  • My apartment building has poor cable wiring/routing.
  • My cable Internet connection has been out, but TV is generally fine.
  • Likely cause is in another apartment(s). It will probably be difficult to coordinate with their tenants.
  • Hypothesis: A tenant has installed a splitter ahead of my connection.
  • Would a cable booster help?

Edit to update/clarify topic summary.
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Old 03-23-2008, 11:19 PM   #2
Elstupido
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Default Cable Internet connection out, TV fine; Weak signal

This is a very complicated situation, all depends on how the cable company has things set up. Sometimes they will over amplify the signal into a complex and use different passthrough splitters. In other words they may use say, a 6db loss splitter on the first tap, pass trough to the next, 5db on the second and so on and on.

To try to give you a simple answer, yes a booster can give you incredible results on a weak signal for TV. I have used a 20db booster from home depot, with great results. The booster however will do nothing for your internet connection.

Add to the mix the possibility of one bad coax termination and or spltter, and you have a real problem. I would amplify your signal for now with a booster and have your cable company check out the entire system ASAP.

It is possible that when and if they give you a strong signal, you will need to disconnect your booster, as you will then have an over amplified signal which will make your TV unwatchable.
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Old 03-25-2008, 09:13 PM   #3
Texun
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Default Cable Internet connection out, TV fine; Weak signal

Yep, it can get complicated until you know exactly what it causing it. From what you have described you have a loop system- one line feeds one apartment and another and another, etc. In a looped system the cable company should be using directional couplers (taps) for each apartment, but in many cases they use a splitter, which cuts the signal by 50 or 100% depending on the type used. Example: If you have 7dB in and install a 2 way splitter you lose 3.5dB or 50% but if they use a 4 way you lose 7dB or 100%. Modems prefer an input of -5dB to +5dB but they can often be fine at twice that spread. Do you happen to have a Motorola modem? If so try this and check the signal levels there. A directional coupler is designed in a "T" shape whereas a splitter will usually have 2-4 ports on one end and a single input on the other. DC's usually have one port marked with a number indicating the signal drop. It's usually 3, 6, 9, or possibly 12dB. The lower the number the better. Higher numbers attenuate or drop the signal level according to the number on the port or tap.

If an amp would work the tech should have added one for you, but not if the levels entering your apartment are too low. Amplifying signal that is already too low only amplifies the noise in the line and does little or nothing for the connection or reception. Another hurdle with amps is that many will not amplify the signal for the return path. The modem must "see" the CMTS (big router) Each time you click on a link a signal is sent back on the return path to request the page you want to load. If the amp isn't built to amplify the return it is highly unlikely that the modem will ever link up because it needs to establish and hold a return path to communicate with the CMTS (think big router). Naturally if the modem won't link your page request will never be seen.

You have a problem that should be fixed and not patched with an amp. Amps should be used only when the resident has multiple devices requiring more signal than is available, and then only connected at a point where the signal levels are still good enough to be clean and free of noise. Normally they should be the first thing connected in the resident's line.

If you still want to try your own amp be careful not to go too big. Too much amplification can cause the same problem as not enough. A 10dB boost applied at a point where the levels are still clean is usually more than enough for 4-6 TV sets, VoIP, and a cable modem. The 10dB number is a general rule of thumb and can vary depending on the input levels but it's a safe place to start. If you need more than 10dB then it's highly likely you could resolve the TV problem but not the cable modem problem. The reason for this is in paragraph 2 because the unamplified return signal from the modem would never make the trip back to the CMTS to establish a solid link.

Loop systems are a crappy way to deliver serves now days. You really should grab the cable company by the horns and insist that they make repairs and deliver the service you are paying for. They should also give you an adjustment on the services you have not received.

Hope this helps!
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Old 03-26-2008, 05:18 PM   #4
The Bakery
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Default Cable Internet connection out, TV fine; Weak signal

Had a similar problem recently, up down up down.

It was a severed coax mesh 3 feet behind the wall causing the modem to drop, but the television (downstairs) was fine.

If your TV is funky, then the signal coming in could be damaged or weak. I would say that you can couple the connection
so that more signal will reach your internet split in the meantime, and less to the TV.

Of course that's a temporary solution. In an apartment complex you really need a tech to resolve that.

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Old 03-26-2008, 11:47 PM   #5
Dessert Tears
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Default Cable Internet connection out, TV fine; Weak signal

Thanks much for your replies. I've been doing a bit of reading in the past few days, so I know significantly more than I did before, such as how to read the modem diagnostics page and how a booster works.

I have a temporary fix in place: I replaced my -8dB TWC splitter with a new -3.5dB one. Before I made the purchase, I removed the splitter and connected the modem with a coupler, which worked with significantly better incoming signal strength. I had previously tried to connect the modem directly, but I think I made a mistake then.

Received Signal Strength, according to modem (the time of day and frequencies don't exactly match, but the differences are significant)
  • Old splitter: -21.0dBmV ? no connection
  • Coupler: -10.1dBmV ? successful connection
  • New splitter: -13.3dBmV ? successful connection
With the old splitter, the modem was unable to acquire a connection on the return path, which an inexpensive booster would not amplify.

I was able to make contact with the tenant of the likely apartment. She was quite accommodating and allowed me to look at her cable connection. The wall box had no plate, and all the lines were clearly visible. I saw 4 lines total: 2 coupled together, 1 feeding a 1?3 splitter, and 1 connected to an output of the splitter. The other 2 outputs of the splitter supply the apartment's TV and cable modem. In line with my previously stated hypothesis, I'd be willing to bet that I am receiving the signal from the splitter. I am curious about the coupled lines and whether the installing technician moved the splitter from there to my line or installed the splitter in lieu of a tap.

Proper resolution of the issue is now dependent on getting a knowledgeable tech to examine that wall box. Unfortunately, the tenant has a full schedule and has no vested interest in scheduling a service call, so it may be a while.

Edit to clarify: The modem is now successfully connecting.
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Old 03-27-2008, 01:29 AM   #6
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Default Cable Internet connection out, TV fine; Weak signal

You made great progress and you are very close! The 13.3 dBmV is just outside the modem's comfort zone. If you could get it to -10 or better, chances are good that your troubles would be over. What is the TX level. I'm guessing well in the 50's. Anything you add to the cable feeding the modem will increase the TX and drop your input level.

I may not be reading your reply correctly, but are you saying you tried connecting the modem directly to the cable without any splitter? When you refer to the coupler are you referring to the connector on the end of the cable? I would certainly try the modem right off the wall plate with no splitter if you haven't done so already. If you try it and the modem holds, then adding a small 7-10dB amp right out of the cable feeding a splitter may help. I am guessing you have a Motorola modem. If so you have one of the best you can get. Motos are able to manage through noise that others cannot.

If it links up right straight off the cable with no splitter, and your TX is below 55dB, you have 2-3 dB of headroom on the TX before the modem will drop off. Adding a splitter will increase your TX by the number on the splitter. So if your TX is 55 and you add a splitter you will see a TX of 58-59 which would not be in your favor. If it's below 55 you may be able to add a splitter and be okay.

Some modems will drop if the TX is above 55 while others of the same make and model will go to 58. Once the TX goes above the mid 50's there are no guarantees.

If a direct connection works and you want to use an amp you can try this:

Wall Plate >>> amp>>>> 2-way splitter connected to the TV and cable modem.

Not- Wall Plate>>>> splitter>>>>amp>>>> TV and Modem

If you need to use a 3-way splitter you will see 1-3.5dB and 2-7dB ports. Be sure the splitter is connected after the amp and that your modem is connected to the 3.5bB port.

*edit* The TX (transmit) is also known as your Power Level.
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Old 03-27-2008, 11:06 PM   #7
Dessert Tears
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Default Cable Internet connection out, TV fine; Weak signal

Texun, thanks for your help. I've clarified my posts to note that my modem now successfully connects, now approximately 24 hours without incident. It's a precarious position, so I will monitor the modem's event log and continue to move forward on the service call. I'm planning to delay any equipment purchases until the service call and the TWC solution.

The modem is a Thomson (branded RCN) DCM425. The return path "Power Level" has been 60.5 dBmV each time I have checked the diagnostics.

I originally tried the modem directly on the wire coming from the wall, male F connector to the modem. That didn't work, probably due to user error. Yesterday, I tried using an additional short cable, connecting that to the wall with a F/F coupler. This succeeded.
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Old 03-28-2008, 12:11 AM   #8
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Default Cable Internet connection out, TV fine; Weak signal

Quote:
Originally posted by: Flatscan
Texun, thanks for your help. I've clarified my posts to note that my modem now successfully connects, now approximately 24 hours without incident. It's a precarious position, so I will monitor the modem's event log and continue to move forward on the service call. I'm planning to delay any equipment purchases until the service call and the TWC solution.

The modem is a Thomson (branded RCN) DCM425. The return path "Power Level" has been 60.5 dBmV each time I have checked the diagnostics.

I originally tried the modem directly on the wire coming from the wall, male F connector to the modem. That didn't work, probably due to user error. Yesterday, I tried using an additional short cable, connecting that to the wall with a F/F coupler. This succeeded.
60dB is the max transmit limit for a cable modem. Many won't lock and hold above 58 but if your modem is working at 60dBmV you are among the few fortunate ones. I suggest pushing TW to make it right. Get a supervisor or manager involved if necessary. Once summer gets here and temps start to rise, your 60dB may not hold because heat causes cable to expand, expansion adds length to the physical plant, and additional length causes attenuation in the signal level. Gain controllers are used to automatically adjust for these minor variations but they are not always stone solid. Maybe +/- 1dB. At 60dB you are maxed out and have zero headroom.

Best of luck and happy surfing!

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Old 04-06-2008, 12:37 PM   #9
Dessert Tears
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Default Cable Internet connection out, TV fine; Weak signal

The TWC technician replaced the 3-way splitter in the source apartment with a 2-way splitter. This change restored all my TV channels and improved my Received Signal Strength to -9.0dBmV and my Power Level to 56.5dBmV.

Thanks for all the help!


How often is Internet "speed" (web browsing, downloads) affected by cable signal strength? My assumption is that, aside from the modem not being able to hold a connection, "slowness" is caused by heavy usage by other users. However, I found a FAQ that says that signal strength may have an impact.
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Old 04-06-2008, 03:35 PM   #10
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Default Cable Internet connection out, TV fine; Weak signal

Glad you got them to improve the levels. The return is still in the high range but as long as it remains stable you should be fine. Happy Surfing!
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