Ok, just waiting on Comcast to show up today. I’m seeing what looks like a significant amount of attenuation on my cable TV signal. If you are reading this, then you know that the issue has been resolved one way or another.
Cable is delivered to my apartment through a distribution box located in a locked room somewhere in the complex. I think it’s in the basement of the building I’m in for this building, as the cable feeds from a pole to my building.
I checked with a couple of neighbors yesterday, and they are not reporting any problems with their signal.
Once the signal gets into my apartment it goes through a splitter that sends half of the signal received to my cable modem, and half to my video systems. That is split again, half going to a HDHomeRun receiver (it gets split again there as a result of there being two separate tuners to feed.) The other half is split in 3 feeding my analog tuners.
When I lost my cable modem connection yesterday I ultimately tuned in one of the analog tuners and effectively did not see a TV signal. That’s not entirely true. What I did see was not an acceptable TV signal. If I watched long enough I could see enough of the picture to show that there was a signal, however the signal level was so low that it was mostly snow.
This morning I went and picked up a length of co-ax that I could plug directly into the wall where the cable plugs in, and attach it to a tuner. I was able to see a signal at that point. It did include some snow, but it can be watched. Audio is acceptable.
I then plugged in the cable modem directly into the wall, it does not receive an acceptable signal. I put the first splitter back before the cable modem, and plugged the other tuner into the other output. I can see a loss of signal quality just across that splitter. The signal is expected to degrade.
If you look at a coaxial cable splitter you will see one port labeled ‘In’ and the other ports marked with a ‘db’ level. You may also find it tagged with additional information, such as the frequency range that the splitter works across. 2-way splitters are almost always a 3db loss on each output. That’s because they are splitting the signal across those two interfaces. 3db just happens to represent half of the signal level. Now the actual signal level is often not quite as high as 3db down. There is signal loss for every connection you make in a coaxial network, beyond the actual split. Also there is some loss due to the type of cable in use. Coaxial cable, even the very best, will loose some signal just by the length of the cable involved. So shorter cables are always better than longer cables. Likewise fewer splitters are preferred. If not always doable.
Looking at the description above, The Cable Modem should be at -3db from the signal level at the wall. The digital tuners should be at about -9db, and the analog tuners are going to be at about -12db. My experience up until yesterday was that -12db was on the edge for one tuner, but reasonable for the other tuners. It could be the cable that the one tuner has feeding it, or the strain on the connection.
So now I wait on the cable guy. It would really surprise me if the guy was named Larry. I’m not sure I would be amused.
Of course if you are reading this, I’m not waiting on the cable guy any more. 
