Computer envy drives multi-task addiction

I hit rock bottom last week, sitting at the computer in the dining room and twisting my neck hard to the right to monitor a sporting event on television in the living room. What I got, other than a stiff neck, was impaired comprehension of both activities.

My TV Tuner card seems to need more signal strength than a normal TV to get a decent picture. The problem with that is: I already have 7dB of splitter loss even before I add another splitter so the digital cable box and the TV tuner card can both be connected.

If I disconnect the cable from the digital cable box and plug it straight into the TV tuner card, the picture has interference lines in it, almost as though the tuner module is picking up interference from inside the PC (which it might well be).

If that's the case, the low signal level certainly isn't helping the signal/noise ratio.

I suppose I could use the video/audio outputs of the digital cable box and connect them to the computer, but I shouldn't have to.

I ought to call Comcast and have them check the signal levels (I haven't found a reasonably priced signal level meter anywhere..)

Do you have a cable modem? If so, you can query the modem and get the signal levels. Click on this link: Cable Modem Home Page. The link uses the standard address that most use. You'll want to look at the "Downstream Power" and the associated "Signal to Noise Ratio". The DP at the cable modem should be greater than -15.0 dBmV and the SNR should be greater than 25dB.

I had trouble with the video quality at my machine (several splitters, etc.), checked the modem info page, and found that my signal level was too low coming into the house. I added back in the splitter dB loss and found that the house level was something like -10dBmV when it should have been >= 0dBmV. Because of this, my SNR was only 18dB or so.

Called the cable company, they came out, verified the low levels, and ran a new line from the street. I was losing 9 dBmV from the street to the house! They also installed a three way splitter outside and fed the higher power output to the line going to my computer. The result: better video quality and my digital channels don't crack up when it gets warm outside.

Oddly enough, though the levels at my cable modem were below minimum specs, my cable modem always worked perfectly. Very high speeds (2900/120) and no noticeable trouble.

BTW, if you don't have a cable modem to query via your browser, you can get the power levels from a special mode on your digital cable box. On mine, you press and hold the info button while turning on the power. There are several status pages with power levels, SNR, data rates, etc. Pretty interesting geeky stuff.

My cable modem reports -5dBmV (usually). It varies, and I've seen it as high as +5dBmV (usually when the weather is colder, maybe the temperature compensation in one of the amps isn't working so well..)

An analog signal needs to be a minimum of 0dBmV for crystal-clear picture. (This corresponds to 1000uV/1mV at the antenna terminals. Actually this figure was developed for a typical 1960s TV set, modern TVs are somewhat more sensitive, perhaps able to display a clear picture down to -3dBmV, but good engineering practice dictates 0dBmV as the minimum level)

Most cable companies run the digital signals at a lower level than the analog signals, so the analog signal is most likely somewhat above -5dBmV. How much above, I don't know.

I was having trouble with my cablemodem (usually it would crap out in the morning) so I checked all the connections and found that the connectors that were on the cables when I bought the house (which were not replaced when they hooked the cable up) were loose. You could yank them right off the end of the cable with a firm tug.

I called Comcast and they sent someone out who replaced the connectors and the cable modem has been working fine since.

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