[mythtv-users] PVR-150 MCE captures nothing but static
Brian Wood
beww at beww.org
Sat Jun 24 03:13:19 UTC 2006
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.
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