I am having difficulty with my cable provider (comcast). Through the cable box, a number of channels exhibit tiling, audio dropouts, or are completely black. When I view these same channels directly on my television (to the limit of its 99 channel tuner) they come in, albeit a bit fuzzy. In addition to this, my internet speed rarely approaches the paid for 8 meg, typically it's 5 meg or less. I'm wondering if this is a signal level issue. I have a 60 mhz oscilloscope. Can I use this to directly measure the signal at the cable outlet, and if so, what levels should I see? Comcast has been less than stellar in its response to these troubles, maybe if I can measure the signal levels I can at least determine if the problem is a low signal to the house, or originates in the distribution (cables, splitters, associated connections) internal to the house.
This may or may not be relevant to your situation - I can't tell without more info.
If you have high speed cable Internet (which it sounds like you do), your cable modem measures signal strength, and you MAY be able to read the actual measurements. For example, I have a Motorola Surfboard modem, and whoever is out there at http://192.168.100.1/ will tell me the signal levels at the modem, both uplink and downlink.
You can also go to BroadbandReports.com and run some error-rate tests. These don't tell you the signal level directly, but a high error rate can be very indicative of low signal levels. It is quite sesnitive, right around the threshold level.
In my neighborhood, Cox cable gives me very good service, but they really don't want to muck with the neighborhood-wide signal levels. I understand why - there is a delicate balancing act between signal levels and interference/distortion. If they crank up the Internet signal, it produces interference in some of the cable TV channels. If they crank up the cable TV channels, it produces interference in other channels. Etc etc. Last time I called the Cox tech out, he agreed that the incoming Interent level was too low at my location, and the solution was to install a bi-directional amplifier right at the service entrance to my house. This boosted the incoming Internet signal (but not the TV channels) coming into my house. He set the amplifier to simply "bypass" on the outgoing Internet signal. The neighborhood is happy, since nothing happened out there. I am happy, since 6 dB more downlink signal solved all my problems. Good solution!
Bill writes good stuff. I'll just add that Comcast is very responsive to the these issues and you should first try their technical support. Has always worked for me and at no extra charge.
I agree. When I first got Comcast internet service, I had intermittent service... slow login, sometimes unable to login, disconnects, etc. I called Comcast and the tech they sent out fixed the problem on the first visit. The original installer had run an extension to my computer from the back of my main TV, where the cable was split to the rest of the house. The run from the pole to my TV set is probably 175 - 200 feet when all the turns and bends are accounted for. The tech looked at the signal levels, put a splitter in the line at a point closest to my computer, and ran a separate line to my computer. He said that increased the signal at my computer by about 3db. Haven't had a problem since (except for when hurricanes knocked it out for over 2 weeks). In retrospect, I probably need to replace all of the RG59 in my house.. it's about 25 yrs old by now {:>)
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Dave M
MasonDG44 at comcast dot net (Just substitute the appropriate characters in the
Bill et al- thanks for the replies and Bill especially for the very useful site referral, I'd never seen that one before. I do have a Motorola modem (SB5101). The downstream measurements are 711 mhz (so much for the 60 meg scope ;-/ ), SN ratio of 34.9 dB & power level of
-6.7 dBmV. Upstream is 23 mhz, 36.5 dBmV. If you can give me any insights into the implications of these numbers, I'd appreciate it. Also, what are they referring to on the page under "LOGS"? I see they go back a month, are these stored in the modem? There are quite a few entries reading "SYNC Timing Synchronization failure" of various types, is this a problem?
As to calling comcast, I have repeatedly, they've sent out 3 guys, the first 2 essentially did nothing, the last "jerry rigged" (to use his term) the connector at the box end, saying the buried cable was of a type they no longer support, and that most "techs" don't know how to do this. This was 2 weeks after the initially "installation", despite talking to several supervisors & an individual at their engineering department & asking them to at least run a temporary line until the repair could be effected, since I need the Internet to work from home. I was told in a phone message from engineering that though I had NO service, a temporary line "is not required". I don't doubt they may be more responsive in areas where there are alternatives to their service, that's limited here, especially for true high speed Internet (6-8 meg, as opposed to .7-1.5 meg DSL), and in my experience their customer service has sucked. On my most recent contact, I told a "supervisor" if something wasn't done once and for all I'd have no choice but to cancel my account. Without skipping a beat, she replied "would you like me to go ahead and put that cancellation through now?" What an attitude. Finally she said she'd "make a few calls & get back to me". That was about 10 days ago, during most of which time I was on a business trip, and I've heard nothing. I can't wait until there IS an alternatve to the bastards. My previous cable company in another state was Wideopenwest, I nver had a problem with them, though I'm sure there are those with a different experience. Anyway, after replacing a wall jack yesterday & cleaning up all internal connections involved the tv portion is satisfactory (for the moment, knock on wood) but Internet speed (I do use BroadbandReports.com) is still typically 60% of what it should be.
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ And here are my numbers Down 579 MHz SNR = 34 Power = -5 Up 19.599667 MHz Power 44 dBmV
I think the power level of -5 is OK. I seem to remember reading somewhere that it should be above -10, and sure enough when mine was -10 was when I was ahving the trouble. The amp I spoke about is what raised it to -5, and now I have no trouble.
Did you dig down into BroadbandReports.com? They keep changing the page layout on the opening page, and it looks like they have reached a new high in uselessness. But if you go down to
formatting link
and start looking around, it is a lot more useful. In particular, I came across an entire section on Cable Modem and Wiring Issues, and it touches on signal strength issues.
There is an entire saection on Comcast, one on Cox, one on Adelphia, etc.
Sorry that you are having trouble with Comcast ... that is not typical ... I wonder what is different in your case? I'd suggest going to the top with a letter or two. I find that letters have much more impact than emails and phone calls.
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