[mythtv-users] Image Quality PVR-500
Brian Wood
beww at beww.org
Wed Feb 21 02:55:22 UTC 2007
On Feb 20, 2007, at 5:48 PM, David Brodbeck wrote:
> Brian Wood wrote:
>> Some people have said that the tuners on the capture cards are
>> pickier about levels than the ones in TV sets, but I'm not really
>> sure I believe that, because I would think they are using the same
>> tuner modules that are used in TV sets, why design a totally
>> different unit?
>
> I've always suspected the problem is a tuner card lives in a very
> noisy
> environment. That limits the amount of amplification (and hence AGC)
> they can put on the card, because it would end up amplifying noise
> from
> all the other components in the computer.
Well the RF can is supposed to be shielded, but it has a press-on
lid. I've said here before that I have had in the past problems that
were solved by a dab of solder on each side of the can top.
Of course the bottom of the can is open to the board, and unless
there is a god design, like using one of multiple layers as a ground
plane, crap can get in that way.
But noise can certainly get in after the RF can, in the baseband
sections of the card. You really can't expect great design for $50,
and as you said the inside of a PC case is one of the most
horrendously noisy environments that can be conceived.
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