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Thread: Guide for fixing lost connection and speed issues on cable.

  1. #1
    The Mad Scientist! Rocky_Grim's Avatar
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    Guide for fixing lost connection and speed issues on cable.

    Cable Troubleshooting Guide
    How to fix speed issues and connection loss on cable
    04.26.2006 08:46 EST by Rocky_Grim



    This guide contains information for fixing issues with cable, mostly compiled from a friend who works for Adelphia cable here in New Castle, Pa. This guide will aim at resolving lost connection and slow speed issues by yourself. You should also try tweaking in addition to those suggestions. After going through the steps in this guide, if you are still having problems with your speed, you may need your cable company to come and replace the cable line from the pole to your house. The cable run from the pole could be damaged, old, or have water in the line. If you are still having problems staying connected after that it is most likely on your ISP's end. Contact them and have them look into the problem. If they don't resolve the problem in a timely manner, or can't, changing ISP's is usually possible. Anyway here are some steps you can take to ensure the best signal levels at your end:



    Remove unnecessary splitters.

    1. Take a look at your cable wiring in your house. Trace the one that is hooked up to your cable modem to wear it is split at.
    2. Find the wire that is coming into your house. It will be plugged into a spliter that slits the cable to all your tv's.
    3. Go to Radio shack and buy some good RG6 cable that will reach your modem. Also get a splitter that says "IN" "OUT" and "TAP". Most cable companies call this a "DC" short for direct connect. Because when you use it this way it does not drop the signal level any amount of decibles like other splitters. Make sure it is a all gold plated one and goes up to 1,000mhz or better. When ever you split anything you want to make sure you get a good splitter with gold plating for optimal performance and good connection.

    Once you have all the correct parts, follow these steps.

    1. Get your main cable line that is coming in from outside and disconnect it from the splitter that it is plugged into.
    2. Take your splitter the one that is labled "IN" "OUT" and "TAP" and then you are going to perform a "DC" or direct connect. This will be a direct connection staight to your modem from outside. Plug the main line into the "IN" and get one piece of cable wire long enough to go to your cable modem and plug it into the "OUT" and plug one peice of cable wire to where it says "TAP" and plug it into the main slitter in the house that goes to all your TV's.
    3. Check your signal levels again and see if your signals have improved. Run some speed tests. If you perform everything correctly you should have a better signal level to your modem which will intern provide a faster more reliable connection.



    Find your cable signal level.

    Many cable modems have web based self-diagnostics showing the signal leve. To find out how to access the signal levels on your particular brand/model, either find the manual from the manufacturer of your modem, or check the SG Hardware Database

    For example, for the Motorola SurfBoard series modems, navigate to this page: http://192.168.100.1/ . You can post what your signal levels are in the forums, and someone can interpret them for you. Generally, power level should be between -5db and +5db for best performace. That can tell if there is a problem on your end with the wiring and signal that you modem is recieving.



    What do those signal levels mean?

    For diagnostic purposes, the cable modem can measure and report the Downstream Received Power and the Downstream Signal-to-Noise Ratio (SNR). The SNR is important because if there is too much noise on the cable, the data cannot be decoded correctly, even with downstream power levels within acceptable limits. If the SNR is good enough so that the cable modem is working correctly, the exact power level, even if slightly outside normal ranges, does not matter.

    Downstream SNR: should be 30 dB or higher: the higher the better. As the SNR decreases below 30 dB, performance will steadily decrease, and errors will increase. The cable modem might stop working properly if the SNR drops below 23.5 dB.

    Downstream Received Power: the DOCSIS specification requires cable modems to function correctly with downstream power levels in the range -15 dBmV to +15 dBmV: power readings at or close to those extremes are likely to be unacceptable. However, when connected to a real-life CATV network, a cable modem might be functional over a narrower range than this. Accordingly, cable ISPs will specify an even narrower target range when commissioning their network: this target range will differ according to ISP.

    Target Commissioning Range Wider Working Range
    NTL original areas -2.5 dBmV to +2.5 dBmV somewhat wider than that!
    NTL ex-C&W areas -6 dBmV to -3 dBmV -12 dBmV to -3 dBmV

    Provided the Downstream SNR is acceptable, the downstream power should be satisfactory if your cable modem reports a figure either within these specified ranges or close to them.

    If a cable modem reports a downstream receive power of exactly 0.0 dB, this means that measurement of downstream power is disabled, and no information is available. In this case, you will need to judge downstream quality by SNR alone.

    Upstream Transmit Power: The cable modem's Upstream Transmit Power (or return power) is set by commands from the UBR so that the UBR hears the same signal level from all cable modems on that upstream channel. Because of different cable losses for each cable modem in the area, each cable modem will tend to settle onto a different upstream transmit power level. The better the return path is, the lower the upstream transmit power will be.

    The upstream transmit power will lie within the range +8 to +58 dBmV, with many ISPs specifying a target commissioning level below +55 dBmV. Values in the forties are the most common. Many cable modems are unable to transmit any more powerfully than +58 dBmV. One cannot tell how far this is below the figure that the UBR would need to see a strong enough signal at its end to maintain satisfactory performance, so a figure as high as +58 dBmV is normally a sign of an unacceptable return path. If other problem symptoms are also present, an upstream transmit power of +58 dBmV would constitute valid supporting evidence for requesting technical support from a cable ISP.

    The upstream SNR can be sensed only at the UBR, so cannot be discovered by end-users.



    Other considerations.

    The external cable infrastructure is affected by weather conditions, so it is normal to see power levels fluctuating slowly with temperature. If your cable signal conditions are marginal, the CM might stop working in certain weather conditions, and recover in others.

    However, rapidly fluctuating power levels might be a sign of a failing amplifier in the ISP's network, or a bad cable connection, and should normally be investigated.

    What does a DC connector look like?

    Where can I get the DC connector that I need?http://www.accessorywarehouse.com/sh...roductid=12958
    The DC connector you buy should have no more than a -6db drop on the "TAP" end preferably -4db. Any more and you could end up with static on your TV's! If this happens a amplifier on the line to your tv's may need to be put in.

    If you have any questions please contact me and I will do my best in helping in any ways I can. If anyone see's any errors in this guide please let me know and I will update it.

    Thanks for looking and I hope it helps.

    Rocky
    Last edited by Rocky_Grim; 04-26-06 at 08:22 PM.

  2. #2
    Administrator Philip's Avatar
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    Thank you for posting this informative guide !

    It has been posted to the main site as well:
    http://www.speedguide.net/read_articles.php?id=1686
    Linux is user friendly, it's just picky about its friends...
    Disclaimer: Please use caution when opening messages, my grasp on reality may have shaken loose during transmission (going on rusty memory circuits).
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  3. #3
    The Mad Scientist! Rocky_Grim's Avatar
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    Thanks Philip! My buddy came over a couple of days ago and fixed mine all up. I was having trouble with the speeds being consistant. I almost thought it was my router. Then I was like well it was working good before. I said let me get my buddy over here to help me check this stuff out. Sure enough it was all those blasted splitters and amplifiers messing up the signal. Before this I was getting about 4000ish download speeds and like 800 upload on my 7mb/768 line. Now I'm seeing speeds around 7200/900 consistantly!!! I'm not saying that this is the problem for everyone but definatly something to look into.
    Thanks again Phil,
    Rock

  4. #4
    The Mad Scientist! Rocky_Grim's Avatar
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    If this guide is helpful to you please let me know by posting here.

  5. #5
    Regular Member buckifan's Avatar
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    This a very useful guide but I have to take issue with your description and use of directional couplers.

    3. Go to Radio shack and buy some good RG6 cable that will reach your modem. Also get a splitter that says "IN" "OUT" and "TAP". Most cable companies call this a "DC" short for direct connect. Because when you use it this way it does not drop the signal level any amount of decibles like other splitters.
    There is no free lunch and a directional coupler is not a splitter (combiner). There is loss between the IN and OUT ports of a DC depending on the tap value. A DC with a 6db tap will have a throughput loss of approx. 1.3db. A 8db tap DC has a throughput loss of .8db and so on.

    Besides cable another common use for directional couplers is the monitoring of forward and reflected power such as with a VSWR meter.

    The DC connector you buy should have no more than a -6db drop on the "TAP" end preferably -4db. Any more and you could end up with static on your TV's! If this happens a amplifier on the line to your tv's may need to be put in.
    You will be hard pressed to find a directional coupler with a tap value less than 6db. It's theoretically possible to design a DC with a tap value of 4db but it far more practical to just use a splitter with a port loss of 3.5db.

    I also disagree with having the TV's connected to the TAP of the DC. A lot of people have more than two TV's and need to use a four-way splitter. Add the 7db loss of the splitter to the 6db loss at the tap of the DC coupled with any cable loss and picture quality is going to suffer. It is better to connect the TV's to the OUT of the DC and the cable modem to the 6db TAP. Installers that use directional couplers are instructed to use them that way.

    Keep up the good work.

  6. #6
    The Mad Scientist! Rocky_Grim's Avatar
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    You always want to get the best original signal you can get. There for you want to use the "Out" for your modem. That way you only suffer about a 1db drop. About the 6db drop for the tv's you might need a amplifier. I have a amplifier hooked up to mine. You don't want to have to use a amplifier on your cable modem. If not measured properly you can feed your cable modem to much power and lock it up!

  7. #7
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    -double direct connectors?

    -i was wondering if anyone had tried to use a dc to dc to splitter combination, or if that was even feasible? thanks.

  8. #8
    SG Wizard Ashdaw's Avatar
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    I wish I could do that but most of the Cable is inaccessible. We just have to put up with what we have.
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  9. #9
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    Guide for fixing lost connection and speed issues on cable

    Hi all. i have try it but i cant connect to my modem when i plug oaxial cable. If i only connect power and cat5 cable i can see my router but i think the report of my moden is not good until my coaxial cable is connect. I have a webstar modem. someone can help me.

    Thanks

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