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HD5500 Problem with QAM256 channel 82 and 84 only
PostPosted: Tue Sep 26, 2006 8:53 am Reply with quote
heckheck
 
Joined: 26 Sep 2006
Posts: 2




I've finally got my HD5500 installed and running for my Comcast QAM256 cable in Chelmsford, MA. It works fine for most channels, but I'm having a real problem with the signal on channels 82 and 84. The other channels work just fine. I know the channels are there, since my HDTV set is split off the same cable and can recieve them just fine (flipping back and forth from MythTV to actual TV broadcast).

At first, these channels didn't show up in the MythTV 0.20 scan, or in the scan util from dvb-utils package in Debian. I was finally able to get them one time and azap showed me that they were there and locked. Myth was then able to find them too. Since then, they have disappeared again. When I used scan I tried every cable standard available. HRC, IRC, standard and the HRC/IRC EIA varients. HRC totally didn't work. IRC seems to have the same mapping as standard for channel 84 (585000000 QAM256), while EIA IRC is slightly different (585012500 QAM256) according to the files included in dvb-utils.

Unfortunately there are two very important networks in these subchannels. Can anyone recommend a way to get this more solid? Could it be I have a bad card? Tonight I will try removing all splitters to the street to see if that helps. Any other suggestions appreciated.

Thanks,

-Jim
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PostPosted: Tue Sep 26, 2006 6:29 pm Reply with quote
xyzzy
 
Joined: 12 Feb 2006
Posts: 225




The tuner is programmed in 1/16th MHz steps, so as far as the tuner is concerned, there is no difference in frequencies 12.5 kHz apart.

Can you not lock on to the signal at all? Or can you lock but just not find the mpeg streams?

If you're having trouble locking, it could be the cable to the HD-5500 is bad. Or you could just have a marginal signal and your TV is ok but the HD-5500 isn't. Computer cards don't seem to have as good of reception as dedicated hardware. Probably has a lot to do with being stuck inside the EMI hell of a computer case and power rails full of noise.
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PostPosted: Wed Sep 27, 2006 8:54 am Reply with quote
heckheck
 
Joined: 26 Sep 2006
Posts: 2




xyzzy wrote:

Can you not lock on to the signal at all? Or can you lock but just not find the mpeg streams?

When it's having problems, it doesn't lock at all. The signal jumps around at about 80% and the SNR is low (high noise).

I've found that the problem may be related to the connector. If the sliding coax sheath that came with the board is fully pushed on, I have problems. If I back it off a bit (not slid on all the way) I can get the channels. I have the cable screwed onto the sheath and haven't touched that, all I'm doing is sliding the sheath in and out and getting different results. Could it be an issue when the sheath hits something, possibly picking up noise? Weird.

Quote:

Computer cards don't seem to have as good of reception as dedicated hardware. Probably has a lot to do with being stuck inside the EMI hell of a computer case and power rails full of noise.


Yes the PC is a nasty environment, but this is no excuse. I've used to work for a videoconferencing company, and we designed sound stages for our PC add in cards. If done properly, you can get a pretty clean signal environment (believe me OP amps love to pick up static hum and hard drive noise). Power is the big noisy culprit most of the time. One of the tricks is to put in a separate ground and power plane on an island in one section of the board and regulate the power to it. Then you put all the sensitive components on that area. We found that most soundcards were designed like crap in comparison. It can be done, but you need a good analog hardware guy.
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HD5500 Problem with QAM256 channel 82 and 84 only
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