QAM channel scan problem v1.3.11 ATI TV wonder 650 pro

[DaveL]

I've been working on this for several days now. My setup is XP, gbpvr1.3.11, ATI TV wonder 650, and using COX basic cable.

The problem is that some public HD channels(QAM) are not picked up in gb-pvr. I know it sounds very much like a signal strength issue, however, I don't think it's the case, because:
1. Catalyst Media center on the same sestup can pick up those channels without problem.
2. The ATI tuner can pick up many more HD channels than my HDTV. (of course those are unknown ones, which is encrypted) This means the tuner card is more sensitive.
3. If I change tuner mode to ATSC, the missing channel actually show up in the preview list. (yes, I know I won't be able to watch them since tuner mode are wrong) But this at least shows the signal is there and the card can see them.

The odd thing is missing channels all having a higher channel id, e.g., I can get 4.1,4.2, 5.1, 20.1...., but can't get 26.1, 26.2, 50.1.

I tried to follow this thread: http://forums.nextpvr.com/showthread.php...ight=tweak
but no luck so far. There are just so many BDA related config to tweak and I'm not sure their function.

One more thing, I have .net 3.5. The wiki said .net 2.0. I'm not sure if I should downgrade. But want to make sure this is the issue here.

[dennit]

I've been working on this for several days now. My setup is XP, gbpvr1.3.11, ATI TV wonder 650, and using COX basic cable.

The problem is that some public HD channels(QAM) are not picked up in gb-pvr. I know it sounds very much like a signal strength issue, however, I don't think it's the case, because:
1. Catalyst Media center on the same sestup can pick up those channels without problem.
2. The ATI tuner can pick up many more HD channels than my HDTV. (of course those are unknown ones, which is encrypted) This means the tuner card is more sensitive.
3. If I change tuner mode to ATSC, the missing channel actually show up in the preview list. (yes, I know I won't be able to watch them since tuner mode are wrong) But this at least shows the signal is there and the card can see them.

The odd thing is missing channels all having a higher channel id, e.g., I can get 4.1,4.2, 5.1, 20.1...., but can't get 26.1, 26.2, 50.1.

I tried to follow this thread: http://forums.nextpvr.com/showthread.php...ight=tweak
but no luck so far. There are just so many BDA related config to tweak and I'm not sure their function.

One more thing, I have .net 3.5. The wiki said .net 2.0. I'm not sure if I should downgrade. But want to make sure this is the issue here.

The thread you referred to relates to DVB-S (satellite). There isn't much there that's relevant to QAM/cable. (The only relevant thing I saw in that thread was the "ignore errors" ticks which should be off.)

The fact that you're having trouble with higher channels makes me think it's a signal strength problem (higher frequencies decay faster), provided they are really higher physical channel frequency, not just higher logical channel numbers. I'd check that out, and remove all splitters for your scan. I understand why you think it's not a signal strength issue, but if you have any splitters in the line, it's worth it to test without them.

Sub could comment on the .NET question.

[sub]

One more thing, I have .net 3.5. The wiki said .net 2.0. I'm not sure if I should downgrade. But want to make sure this is the issue here.

3.5 is fine. It needs 2.0 or higher.

[DaveL]

I already tried to remove any splitter, no luck there.

Some new observations:
1. The missing channel # I mentioned before are virtual ID, the physical channel # are 5-3,5-5,5-6,5-7,5-8. They happen to be the lowest clear QAM channel available, it seems.

2. I can trick gb-pvr to pick the channels by first scan by setting device type as QAM then map available channels; then change device type to ATSC, and scan and map those 4 missing ones. And I can watch them, pretty good PQ. Unfortunately, if I reboot PC, the channels will be gone. Now I have to first set device type back to QAM first, and then set it to ATSC. And they will be there again.

Strange,isn't it.

[dennit]

1. The missing channel # I mentioned before are virtual ID, the physical channel # are 5-3,5-5,5-6,5-7,5-8. They happen to be the lowest clear QAM channel available, it seems.

QAM.ini controls the actual frequencies checked during a scan. Are you sure you are scanning the frequencies that these channels are on? I'd check that.

2. I can trick gb-pvr to pick the channels by first scan by setting device type as QAM then map available channels; then change device type to ATSC, and scan and map those 4 missing ones. And I can watch them, pretty good PQ. Unfortunately, if I reboot PC, the channels will be gone. Now I have to first set device type back to QAM first, and then set it to ATSC. And they will be there again.

Strange,isn't it.

Yes. I've never tried ATSC scanning a QAM signal or the opposite, so I have no idea what this is telling you, but I would think that if you can scan and watch channels set as ATSC, then that's what they are. Are you just picking up leakage of broadcast signals?

To be clear, I'm using the common terms where "ATSC" refers to terrestrial broadcast signals in the U.S. format and "QAM" refers to signals carried by cable. Technically, both signals are ATSC format. The modulation on cable is QAM (quadrature amplitude modulated) and the terrestrial broadcast modulation is 8VSB (8-level vestigial sideband modulation).

[DaveL]

I got the channel info from tuning request like: T:5~P:6... This also matches what I found on the web about QAM programming in my area. So I'm sure this is clear QAM signal, not leakage from air signal.

I'm not sure why scanning QAM signal with device type ATSC even work. It's just something I stumble upon which at least shows the signal I'm after is there. I'm trying to get normal scan works (QAM to QAM). I saw some people manually tweak input frequency here. That's something I like to try if I can figure out how.

[dennit]

I got the channel info from tuning request like: T:5~P:6... This also matches what I found on the web about QAM programming in my area. So I'm sure this is clear QAM signal, not leakage from air signal.

I'm not sure why scanning QAM signal with device type ATSC even work. It's just something I stumble upon which at least shows the signal I'm after is there. I'm trying to get normal scan works (QAM to QAM). I saw some people manually tweak input frequency here. That's something I like to try if I can figure out how.

Whurlston has a QAM.INI manager that may provide some help for you, but if you are sure your QAM.INI is scanning the right channel, and you're getting other QAM signals, I doubt it will change things. DO you have a signal strength meter with the software for the ATI TV wonder 650? I found signal strength was always my issue when I could scan some channels, but not others.

[DaveL]

Thanks. The qam.ini manager is right on target. For those having similar issue, the thread is here. I have to use "center frequencies" to make it work.

A little more detail here: from previous rounds, I already know the problem has something to do with freqency for channel 5. First thing I tried was to check and see what frequency is for channel 5, it should be in the registry key: HKEY_LOCAL_MACHINE\Software\Microsoft\TV System Services\TVAutoTune\TS0-1. As described here.

It turns out that on my pc this registry key does NOT exist. There are freqency tables for other countries (TSxx-1, where xx is country code). But no such key for US cable frequency there (TS0-1). Since default qam.ini uses channel numbers which in turn needs to be mapped to real freqency using this table, missing this table will cause at least some if not all channel freqencies mapped incorrectly. Thus the missing channels during scan process.

One question remain: is the TVAutoTune registry key populated by Tuner's driver? If that's the case, it should be bug for the driver software. Sub, care to comment here?

[sub]

One question remain: is the TVAutoTune registry key populated by Tuner's driver? If that's the case, it should be bug for the driver software. Sub, care to comment here?

These registry settings are not used when you scan QAM channels in GB-PVR. It tunes directly via frequencies for QAM.


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Some general comments though...

Unfortunately QAM support is not officially covered by the BDA spec, so each manufacturer does it a different way. GB-PVR only implements support for the schemes used by a couple of major manufacturers (Hauppauge etc). Owners of other less common devices, like your ATI device, might get lucky if the manufacturer has implemented their QAM extensions in way that is significantly similiar to the Hauppauge scheme, otherwise they're probably out of luck.