[mythtv-users] HD-PVR horizontal bands

Greg greg12866 at nycap.rr.com
Wed Nov 17 21:28:34 UTC 2010


On 11/17/2010 03:46 PM, Christopher Meredith wrote:
> On Wed, Nov 17, 2010 at 2:00 PM, Greg <greg12866 at nycap.rr.com 
> <mailto:greg12866 at nycap.rr.com>> wrote:
>
>     On 11/17/2010 12:20 PM, Brian Wood wrote:
>
>         On Wednesday, November 17, 2010 10:11:58 am Robert McNamara wrote:
>
>             On Wed, Nov 17, 2010 at 9:09 AM, Christopher Meredith
>
>             <chmeredith at gmail.com <mailto:chmeredith at gmail.com>>  wrote:
>
>                 I've been noticing this for a while now and finally
>                 want to fix it.
>                 I'm noticing that on any content captured by the
>                 HD-PVR, there is
>                 a thick band of discoloration that slowly moves up or
>                 down the
>                 screen. It's very faint, and the effect is usually
>                 just to make
>                 the "banded" area a shade lighter. In complex or
>                 fast-moving
>                 scenes, it's virtually indiscernible. But you can
>                 definitely see
>                 it in slow pans or dark scenes. I've tried using a
>                 different
>                 component cable but it still happens.
>
>                 Does anyone have suggestions about resolving this?
>
>             It's good that you tried a different cable as that would
>             have been my
>             first suggestion.  I don't see anything like this, and
>             given you've
>             tried another cable, my next inclination would be to say try
>             capturing off of a totally different piece of hardware
>             (ie, a DVD
>             player, XBox 360, whatever) and see if things are
>             different.  My
>             thought is that your current STB and the HD-PVR disagree
>             in some
>             fashion.
>
>         With NTSC, 60Hz. "hum" will show up as a single or double bar
>         moving
>         slowly up through the screen (because the NTSC field rate is
>         not quite
>         the 60Hz. of the power mains).
>
>         If you replaced the cable with an identical one, it might not have
>         helped. You might try one with better shielding.
>
>         But the problem may be that all your grounds (earths) are not
>         at the
>         same potential, and what you are seeing is AC hum, the amount and
>         direction would vary with the frame/field rate of the video
>         and the
>         frequency of your AC power (50 or 60 Hz.).
>
>         Grounding is a very complicated issue, and simply grounding
>         everything
>         is site is usually not the best solution, as you get multiple
>         paths and
>         varying potentials all over the place.
>
>         The best treatment of grounding issues I have seen is in
>         Tremaine's
>         "Audio Cyclopedia", but that section is hundreds pf pages long.
>
>         But I suspect your problem is either induced signals due to
>         bad cabling,
>         or "common mode" problems due to poor grounding.
>
>
> Thanks all for the good suggestions. I think I am going to experiment 
> with the cable more. The first one I was using was the one Comcast 
> gave me with the STB (because it was already connected). Then I 
> replaced it with the one that came with the HD-PVR, since I assumed 
> that would be best suited for the device (since they included it, and 
> all).
>
> Interestingly, I have had this same problem with two different STBs 
> (first was the SA3250HD, second is a Cisco RNG-150). I think I'll see 
> if I can find a higher quality, shorter component cable, and if that 
> doesn't work, look into the ground loop isolator. As a side note, 
> aren't there devices that can be clipped on to an existing cable? I 
> seem to recall seeing these somewhere.
>
>
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I think you are thinking about a toroidal  coil..Simple to make if you 
have the parts...
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