[mythtv-users] PVR-150 MCE captures nothing but static

[Brian Wood]

On Jun 23, 2006, at 8:20 PM, Robin Gilks wrote:

>
>> Hello MythTV list,
>>
>> I installed the card and myth with only a little difficulty using  
>> Jarod's
>> guide (substituting repos as I am using CentOS and not Fedora  
>> Core).  Ivtv
>> seems to recognize the card at /dev/video0, and I can apparently see
>> what's going on with the card by using mplayer (mplayer -vo x11
>> /dev/video0).  Unfortunately what's going on is nothing but static.
>>
>> Right now I am just trying to view a DVD, so I have the coaxial  
>> cable from
>> the DVD player going into the connector on the card.
>>
>> I am using input 0 ("Tuner")...
>>
>> [root at rockstar etc]# ivtvctl -d /dev/video0 -n
>> ioctl: VIDIOC_ENUMINPUT
>>         Input   : 0
>>         Name    : Tuner
>>         Type    : 0x00000001
>>         Audioset: 0x00000003
>>         Tuner   : 0x00000000
>>         Standard: 0x0000000000003000 ( NTSC )
>>         Status  : 0
>>
>> ...and I have tried changing the channels with ivtv-tune:
>>
>> [root at rockstar etc]# ivtv-tune -c 3 -d /dev/video0
>> /dev/video0: 61.250 MHz
>>
>> What gives?  I have tried googling for this problem but mostly I find
>> either people asking on various forums (with no responses) or the  
>> standard
>> advice--"Try changing the channel."  Any ideas?
>
> Why is everyone obsessed with channel 3?
>
> Is your DVD player REALLY outputting a signal on chan 3? Is that the
> channel your TV sees it on OK (i.e. 61.250MHz)?
>
> There again the channel number depends on what 'zone' you have the  
> card
> set to - cable chan 3 is not the same freq as broadcast chan 3  
> (certainly
> not in PAL country, I imagine that NTSC is the same).

At least in the US consumer devices that output an RF signal normally  
do so on either channels 2 and 3, or channels 3 and 4, usually switch- 
selectable in either case.

The idea is to use a channel that is not used for off-air  
broadcasting in your area.

The FCC will never assign two adjacent channels to the same market  
(channels 4 and 5 are not really adjacent, nor are channels 6 and 7).  
This is to prevent the aural carrier from creating interference on  
the upper adjacent channel. Cable systems are able to operate on  
adjacent channels by running the aural carrier 15-17 db. below the  
visual, as opposed to 10db. down which is the off-air standard, one  
reason why cable channels are more susceptible to "buzz" in the audio  
when bright whites or character generators are on-screen.

With "standard" frequency assignments cable channel 3 is the same as  
off-air channel 3 (61.250 Mhz. visual carrier, with possibly a + or -  
10 Khz. assigned offset) again, in the US.

The result of the above is that virtually every consumer device is  
capable of outputting on "channel 3", hence the "obsession" with it.