Tuesday, June 28, 2016

What Are Acceptable Signal Levels for Comcast for High-Speed Internet Modem to Maintain Audio Streams, Video Streams?

When you have intermittent interruptions in audio streams or video streams while using your Comcast Internet service, you might have a technician come to check your Cable Modem, and the technician might tell you that everything is fine with your modem because the Downstream (Rx) Power Level is in the "Acceptable" range. Then the next day or even the same night you have signal problems again, and you lose a video stream or lose an audio stream connection. You might also see timeout errors, or certain sections of web pages might load a lot more slowly than other sections of the web page. You might notice that you are waiting abnormally long for an embedded Tweet, or Facebook picture, or Google map to appear on a web page. The page seems out of sync. There is a good chance you might have a problem with your Downstream (Rx) Receive Power Level.

In order to have good Internet speed, good web page loading, and well-functioning audio streams and video streams; a household or business must have good signal levels going into the cable modem. Here is an unofficial table that is believed to be accurate or close to accurate regarding downstream power levels that users receive at their Cable Modems ...

Downstream (Rx) Receive Power Level:
-7 dBmV to +7 dBmV "Recommended"
-8 dBmV to -10 dBmV / +8 dBmV to +10 dBmV - "Acceptable"
-11 dBmV to -15 dBmV / +11 dBmV to +15 dBmV - "Maximum"
Lower than -15 dBmV & Higher than +15 dBmV - "Out Of Spec."

Rx = Receive

Comcast techs usually quote the "Acceptable" range when you ask them what levels are "good" coming to the modem. (Note: None of the techs have ever mentioned SNR (Signal-to-Noise Ratio) or QAM modulation. SNR is another factor that could be causing problems, but you can't fix SNR problems yourself.) Downstream (Rx) Receive Power Level problems are probably more common than other problems.

Take note that even if you are too high or too low but within the "Maximum" range you might have problems, such as slow loading pages, pages that don't don't load all the sections of a web page, and audio and video streams that disconnect. You might even have temporary problems when you're are within the "Acceptable" limits but are near the outer limits of the "Acceptable" range.

You can check your own levels by logging into your modem from your own home network while you are at your home or business. The web address to access your modem is usually

The default admin name and password is ...


Here is an example of how to check your levels. From your browser at your home or business connected to your Comcast/Xfinity network, type in your browser's URL address line.

Enter your admin name and password ("admin" and "password").

In the menu at the left, go to Connection: XFINITY Network

You should see a table that is titled "Gateway > Connection > XFINITY Network"

In the table, look for Downstream: Power Level. You can compare your levels to the Downstream (Rx) Power Level at the top of this article. Ideally you want to have levels in between -7 dBmV to +7 dBmV.

If you see a level that is too low (-11 dBmV or -15 or worse), you need to contact Comcast because you need a stronger signal. If you are at -15 dBmV you probably don't have any Internet service at all.  Keep in mind that if have a level like -8 dBmV, changes in weather and temperature can possibly change the signal to a lower level. If you are having intermittent problems, weather conditions might drop your signal "Out of Spec" when you deserve a better signal coming to your house or business. Call Comcast.

If you see a level that is too high (+15 dBmV or even +8 dBmV) you might be able to fix the problem yourself by putting a splitter or a cable coupler in between the Comcast line into your house (or business) and your Cable Modem. A good splitter causes a drop of about 3.5 dBmV (-3 dBmV). Every location where there is a break in the coax cable line there will be a power loss. If you have a power level of +10 dBmV and you put the splitter on the line, you should then see a modified Downstream (Rx) Power Level of 6.5 dBmV. There are also 1-to-4 splitters that drop the signal about 7 dBmV (-7 dBmV). Keep in mind that changes in weather can also increase as well as lower the power level signal relative to the time you observed the readings.

This is a simple solution to the problem of a signal that is too high out of range or near the upper limit of an acceptable Downstream Power Level.   Keep in mind also that other problems can also cause changes in signal. There are situations when technicians forget to cover boxes on utility poles. This causes the boxes to fill with water, which can cause serious line problems. Squirrels can also chew on lines and cause disconnections or signal problems from loss of insulation.  Technicians often work at night. Whether they are working at night or during the day, they might make a quick change on the cable line that interrupts the signal for only a few seconds. This might not be noticed when you are loading a regular web page, but it might freeze your audio or video stream.

Also keep in mind that your audio stream or video stream source may also have technical problems. The source could have line problems, or the source could be overloaded by viewers.

If you are having trouble, try to get your Downstream (Rx) Receive Power Level in the "Recommended" level, which might provide a simple resolution. If you still have problems, then make sure Comcast rules out other potential problems up the line.