Media Center won't properly tune in QAM channels

[xanadu]

Good morning,

I've recently build out a new quiet Media Center box as my primary media center.

My cable signal has well over 100 clear QAM channels available, when I connect the cable directly to the HDTV tuner it happily scans and finds all of the digital and analog channels. Same thing with the WinTV software that came with my Hauppauge tuner cards which are a HVR-1205 and HVR-1600.

The problem is that when I manually add the QAM channels under Media Center it won't tune in the channels most of the time, I just get a blue screen and a notice saying "Service is unavailable" (Weak signal). Once in a while it will suddenly tune in the channel and then all is fine until I tune elsewhere and return, then it may or may not work.

Using the same cable, but connected to my HDTV tuner or the WinTV software I can change between HD channels quickly and with no tuning issues.

I have tried applying KB2708283 http://support.microsoft.com/kb/2708283 (Weak TV Signal message erroneously displayed) but that didn't help in any meaningful way.

My only thought is that maybe Media Center isn't properly switching between the two HDTV cards? Is there a way to specify which one is being used?

Any thoughts? I appreciate any feedback.
-X

[staknhalo]

It sounds like even with the weak TV signal fix, the signal is too low still for Media Center to tune. That doesn't mean the signal is bad (as evident by your TV and WinTV picking it up); just still below Media Center's 'cut off' level. You could try different settings for the registry entry listed here: http://support.microsoft.com/kb/2708283 Just be forewarned I don't know if it will do anything and editing the registry can be harmful to your system, yadda yadda backup.

[xanadu]

It sounds like even with the weak TV signal fix, the signal is too low still for Media Center to tune. That doesn't mean the signal is bad (as evident by your TV and WinTV picking it up); just still below Media Center's 'cut off' level. You could try different settings for the registry entry listed here: http://support.microsoft.com/kb/2708283 Just be forewarned I don't know if it will do anything and editing the registry can be harmful to your system, yadda yadda backup.

Yeah, that registry edit just ups the allowable frame-rate loss before displaying the error message. I don't have a signal issue, as evidenced by the WinTV and the HDTV itself being able to turn in the QAM channels with no delay.

Just to make sure I added a +10dB signal booster, the same issue remains, frustrating.

Thanks,
-X

[xanadu]

Ah, I found this signal strength tool at Huappauge http://www.hauppauge.com/site/support/s ... nitor.html and my signal isn't changing when I turn the booster on or off, looks like it is bad.

My SNR is right around 35dB (Bouncing from 32-36) which is resulting in occasional stuttering under the WinTV app, what is considered an acceptable SNR?

[erkotz]

You could try upping that value higher - 0x32 == 50, which just means it needs to see 50% packet loss before it will throw that flag

[DaveJMathews]

Do you know what type of QAM modulation your cable company is broadcasting on? either way that's a nice signal strength. I am assuming they are using 256 but you never know.

16 QAM: 18 dB minimum. 21 dB or higher recommended.
64 QAM: 24 dB minimum. 27 dB or higher recommended.
256 QAM: 30 dB minimum. 33 dB or higher recommended. 33 min or higher for HD I would say.

You might want to look at the tuner itself. Are you seeing any quick drops in the SNR?

All tuners are not created equal, this is why your probably have no issue with the HDTV but the stutter with WinTV and missing channels on the WMC. I had the exact same issue, the bedroom TV worked great, but the HTPC would pop in and out. Even though I had newer coax throughout the house, I found that the splitter was the culprit. One bad connection can ruin a digital signal. Make sure to use a high end low db splitter as close to the cable company's connection as possible. Also use high quality compression fittings on the ends of your coax. The Avermedia tuner I use works great, but it needs all the help it can get.

NEVER use more than one splitter when receiving digital signal. If you have say a two way splitter and then another splitter down the line this can effect the signal dramatically and without warning you do not just add the loss of the splitter "3.5 + 3.5db loss" they many times multiply themselves. ditch any extra splitters first and foremost.

Keep cables as short as possible, use high quality coax, and only use one high quality splitter, usually the ones the cable company provides are plenty good enough if you have been upgraded to digital. I had to redo my entire home once we dropped analog entirely. The signal levels dropped across the board. I ditched all the second splits that went to the analog t.v's and replaced all the coax in my house. I then put in a low loss 5 way splitter and everything was kosher after that.

You can get a bi-directional amp with no-loss/low-loss in place of the splitter for the line. Not sure if your using cable for your modem as well, but this should improve everything in the home.

[DaveJMathews]

http://www.amazon.com/8-Port-Bi-Directi ... ewpoints=1

A little pricey but I have used this in some larger houses with long runs.