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Intermittent Cable signal

2003-02-01 (updated: 2014-08-17) by

I hope this story helps someone with the same problems I had. I started having problems one day with my cable TV. The picture was fuzzy sometimes. When this happened of course my cable modem would lose sync with the Cable Modem Termination System (CMTS) or be really slow. I called Cox @Home service and told them I was having problems come and check it out.

The guy they sent was somewhat knowledgeable and changed out the cable from the house to the telephone pole. He also told that my grounding block was "out of spec". This little block grounds the cable system to earth ground. After changing all that out my tests on bandwidth were incredible. I went from 100-200kb/s to over 1mb/s. I thought this is awesome!!! Simply changing out my cable and the grounding block shot my bandwidth way up. This isn't the end of the story unfortunately.

About three days later my cable modem went out altogether for no apparent reason! I kept looking at the TV and it looked great? What could be wrong? Called Cox again and this time they started giving me the run around. Oh, it must be your cable modem. We'll send someone out in a week. What the hell? I had to raise a lot of hell but they finally gave me a free month because of the trouble but, it was still going to be a week before someone would come out. I was pretty aggravated about this and decided to take matters into my own hands.

I'm a new MCSE by trade and I figured this would be a good challenge and learning experience. The telephone pole that provides cable, power, and telephone service to my house was the last one in a long line. I guess I'll work upstream. I went to the houses in this long line back the main road to our neighborhood. Only two people out of about 20 houses had cable modems and they were having similar problems. Ok, so it's not just me. I called Cox regular cable TV and lied and said my cable was out. They said no problem we'll have someone out the next day.

The guy came the next day and I said, "oh my cable TV just came back an hour ago but, now my cable modem is out". He left and worked on it for about a couple of hours then came back and told me that my cable TV and modem was going to be out for about 10 minutes. It was and when it came back everything was twice as good as it was before. I didn't think I could get more than 1mb/s but I have achieved during non peak times 1.8mb/s. The problem all along was a intermittent amplifier on the main trunk line that was feeding our neighborhood. The guy told me that the cable system has an amplifier about every 1/2 mile of so. Then why did I have cable TV and no cable modem. He said that the cable signal for TV was very forgiving and it didn't take very much to get it down the trunk line. The cable modem signal on the other hand is a very precise signal and must be very stable and clean.

I hope this helps someone.


  User Reviews/Comments:
by Mike - 2006-03-25 00:58
Yeah sounds pretty familiar. The first guy that replaced your drop did the right thing. Unfortunately the intermitent amplifier was out of his hands but the cool thing is with your way of finagling the system it got you fixed all together...
by exbbandspprt666 - 2006-04-04 09:33
"The cable company is here to educate you arent they?"
by Mr.Cable Guy - 2006-05-21 02:08
typical tv signals are analog. Internet and digital cable signals are digital. Cable amplifiers have the ability to adjust automatically for weather changes (the colder the weather the less attenuation). Areial amplifiers are setup to do this because areial systems are affected by the temperature more so than underground systems. What happens is that this adjustment circuit locks up easily causeing an over- amplification. That digital signal gets clipped off causing cable modems and digital cable to screw up... beware of winter :) btw cox sux
by anonymous - 2007-02-27 02:47
I have worked for two cable companies, one as a service technician and one for high speed internet tech support, and I could name you about 1001 reasons why that would happen. Could be old rg59 homeruns, could be bad drop which is frequently the cause since it is the most exposed to the conditions, also the internet must not be on the house amplifier, it raises the return path and can cause noise and distortion, splitters are another cause, the internet should have a dedicated homerun before the main splitter that feeds the house, this allows the modem a lower return path (upstream transmit power) which will alow a better connection, also yes cable systems have amplifiers and AGC's which are automatic gain controller's if i remember correctly, I have been out of the field for a while, but the agc will adjust the gain according to temperature accordingly, thats why most people have their tv pixelating on digital boxs or internet going in and out around the evening times when the weather cools down.

I hope this helps someone, I know from experience from both companies that techs will tell subscribers some BS since they will not know what the hell they are talking about, but if the signal is low or the return path is too high, but not at the TAP, which is where your drop or cable line to cable co is hooked up is connected, then the splitter or amp or bad cable or many things can influence this the return path isnt as sensitive as the forward path which is a higher frequency and looses moe DbMv per given foot of cable, so typically the cable co I worked for channel 88 was the data channel for internet downstream but the freq. of 29mhz was the upstream I think and is less loss over a given cabling distance, what a splitter loses in downstream it gains in upstream, also make sure the tech uses underground flooded cable for underground drops and aerial cable which is messengered for overhead applications and uses homerun cable in the house for jumpers. Ok, I am done before i get carried away, i am just saying you wont catch the cable co abusing me ever.
by jadwv2210 - 2009-05-31 18:53
I was having the same problem! One day my sync light on my modem was flashing so i called the cable company and the fixed it and said it was my signal. I was even having the same problem with the TV especially when it was cold.
When they fixed it i didnt notice an increase in my download speed it stayed about 100-200 kb/s im going to have to call the cable company and tell them the same thing you did great article
by Ginger - 2010-02-08 14:43
Thank you for your comments. I have been having intermittent internet signals for sometime and cannot get any where with Charter Cable Co. I've been told that if the movies on demand work then the internet should.
I've never had any problems with the cable TV. I throught that was BS but i'm not very computer technical. All a got for my frustration was a $20.00 credit.

Question: Will the amount of subscribers using the internet affect cable internet signal? Charter says 'no' but Sunday during the Super Bowl I had a perfect signal the whole game. Game over and the signal went out. It's the return light that goes blinking.
by carrtb - 2010-12-27 21:13
Thank you Anonymous for your detailed explanation! What you described with the digital TV pixelation and "slow" internet in colder seasonal nighttime hours and in the winter is exactly what is now happening to me.

I started testing internet speed (with a speed test site) and noting digital TV quality in intervals since last June because I was having trouble with my underground service. I called and Cable Co changed my service line from RG6 to RG11 because of my signal strength and I am the farthest of three customers on the pedestal (my house is wired with RG6). Service improved dramatically. Speed tests then clocked at my limit of 10 Mbps download, 1Mbps upload and digital TV had great "reception" on all digital channels. Problem solved for the Summer!

Signal issues returned as climate eased into late Fall with colder nighttime temps and now winter (issues increase with cold in the evening and overnight). I was thinking this time around folks are just using up bandwidth but two things are keeping me from calling the cable company: 1) bandwidth certainly should improve in the early morning hours when everybody is in bed (it doesn't) and 2) upload speeds are always rock solid at 1Mbps no matter what time I test! Two items that just didn't fit the puzzle until now. Thank you!

I have one two-way splitter on the cable thus feeding the cable modem and Cable Co DVR. Cable Co told me last summer that having a three-way (or greater) splitter would degrade the signal strength (dB) even if I had nothing on the spare terminals. I believe I will try putting back my five-way splitter just to see if things improve. This should lower the signal dB to the terminals serving the DVR and cable modem!
by anonymous - 2012-11-03 15:24
ook up the different cable sizes and specs, there is a mathematical formula for cable loss. rule of thumb for rg6 4 db loss for every 50 feet. another thing to remember is splitters have the db loss stamped on them, if they are a quality splitter. also satellite splitters shouldnt be used on cable, they will degrade the signal. the splitter for cable should say 5-1000mhz. and should not be "dc passing".
they should have rubber grommets on them or they will fill with water. they may still work somewhat, but signal will be degraded.

look at your modem diagnostics. usually type in in your address bar but better to look up your modem specs and find out what address is specific to that modem.

so you have signal downstream coming in , this is what signal is used to recieved at the modem and also your tvs. usually the plant is designed at 15 db at the tap for downstream, depending on the freq of the channel. modem ds is usually at + 8 at tap.

the modem generates a signal that goes out to the tap. it is usually starts at 28 db and can go up to 57 max. the modem will automatically ramp up its signal to push past feet of rg6,splitters, water in cable, corroded fittings.
so i would start at the modem diagnostics, and see what the modem is working with. ds should be between -8 and +8 , the upstream will be between 28 and 52 max. the harder your modem has to work the higher ustx will be.

so lets say the modem light is blinking at ds, that means its not getting enough downstream.
if it made it past ds and is stopped at us then it is past max transmit and cant work past all the splitters and bad wiring.
sometimes it will make it through all and lock in ,but internet is intermittant.
usually the us is too high and the modem distorts the signal because it is at max transmit.

so work starting at the tap, assuming +8 DB then subtract 9 db for 100 foot drop then 3.5 for 2 way splitter then 4.5 for a 50 foot run of cable to modem.
leaves you with -8 at the modem the minimum, but it is in spec.

so downstream works out

now upstream, its usually 40 at tap, but its usually at a low freq, which loses less signal with cable size and distance, about 1.5 db per 50 ft. it will still lose
3.5 db on a 2 way splitter, 7.5 on a 3 way.

so say your modem says 58 ustx. so looking at the same system if its 40 db at the tap, add 50ft cable to splitter 1.5, splitter,3.5, 100 feet to tap 4 then your upstream should be 49. if its 58 then there is multiple splitters,water in line or splitter, loose fittings, corroded fittings ,older rg59 line, bad ground block wrong type of splitter ect.

thats just the basics, theres also us snr ds snr , overamplification, tilt, ifcr, for starters, and also that each channel is on a different freq, and therefor is affected differently by all of the above.
by anonymous - 2012-11-03 16:09
every splitter acts as a resistor, a 4 way splitter will subtract 7.5 db , weather anything is connected or not. lots of people think the more things that are connected the more it will "draw" power. this is wrong.
it is running freq of between 22 million cycles to 750 million cycles. it is near the spectrum of radio waves and light waves. no volts or amps here, or very tiny anyway.
your house ac wiring is dependent on volts and amps, works on different physics principals. also if your wall switch goes out do you call the power co to fix it ? no you call an electrician, its your house , your wiring YOU own it !
if you have your phone jack corrode in your house and all your phones are fooled into thinking the phone is off the hook do you call the phone co to fix it ?
no you call an electrician, its your house , your wiring YOU own it !

if the cable is your house is outdated,rg59, your splitters are old golden 600 mhz , your fittings are radio shack twist on , WHO owns the wiring and is responsible for it YOU ARE !
so no more hissy fits about your the cable co. my wiring is crap so fix it at no cost or ill be mad UNDERSTAND!
lots of times we do anyway because its easier then listening to you whine about concepts you either cant grasp or your just trying to get something for nothing.

every utility is only responsible for the line from the street to the ground block, usually ending by the power meter.

everything else you own, otherwise when you didn't pay your cable bill we could rip it all out.
if this makes you mad then you are probably one of those entitled types., and that's a whole nother rant.

Have a nice day !
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