TWC digital cable with Cisco 8640 stb. I'm having signal strength/interference issues with my HD channels starting at about 600 MHz (by "issues", I mean that channels at or above this frequency are unwatchable). For channels at the lower end of the problem range, the QAM tuner will often get a lock, but the signal strength is only -19 to -20db, resulting in a severely pixilated picture and audio that cuts in & out. By ~650 MHz, the tuner often can't lock on to the signal at all. The HD on-demand channels display a "temporarily unavailable" message.
If I remove the STB & connect to my TV's tuner, I can sometimes receive the local HD signals, but many of the analog channels show a lot of "bleed" interference.
From the service entrance, the feed (all cables are RG-6) enters a 2-way 5-1000 MHz splitter: one output goes to the cable modem, the other to the STB. I've replaced every interior cable, and I've even connected the STB directly to the cable entering the house: no change.
TWC techs have been here 5 times, and each time they've checked the signal strength (not sure what frequency, as I've only recently figured out the pattern) and declared it satisfactory.
The big kicker is that the problem is intermittent. Even though it's happening more & more frequently, the signals always seem to be no worse than -18db when the tech is here, which is just strong enough to produce clear HD picture & sound.
I've tried 4 different STBs (2 8300s and 2 8640s) and all have the issue. The problem SEEMS to be worse during prime time, but that may just be because that's when my wife is trying to watch her shows. If I reboot the STB, it will frequently display "E-13" as it tries to download the info it needs, and will then reboot itself every 20-30 minutes until it is successful. Lately, this has taken over 24 hours after the reboot before the system is usable again.
We live in an old neighborhood, so all of the lines are overhead. The problems seem worse during bad weather, but the techs each claim to have visually inspected the line from the pole, and they all say it looks fine. None of my neighbors seem to have any problems (I've confirmed that their channels work when ours don't).
I'm at the end of my rope, and satellite is looking better & better, but my wife doesn't want a dish if we can help it. Any ideas on what it could be & how we can fix it would be greatly appreciated. Thanks.