[mythtv-users] Strange DVB-T Interference Any Ideas

Alex Butcher mythlist at assursys.co.uk
Mon Dec 15 18:35:50 UTC 2008


On Mon, 15 Dec 2008, Charles Mason wrote:

> My problem is without warning a recording will go from no interference
> at all, to completely unwatchable instantly. Its never so bad to
> completely stop the decoding but its just constantly blocky, with odd
> colours, droped frames and nearly intermitent audio. This can last to
> the end of the recording or some times only a few minutes. When it
> does clear up its instant and the video goes back to being 100%
> perfect again. I have checked its definitely on the recording not the
> playback as if its played again it happens at exactly the same point.

That's the problem with digital, really - it reduces redundancy, allowing
more information to be transferred using the same amount of bandwidth, but
at the expense of fragility. As such, digital tends to degrade less
gracefully than analogue. Hopefully things will improve in the UK when
analogue broadcasting is turned off, and the power levels for digital
broadcasts are increased.

> Our nearest neighbour is half a mile away so I don't think its caused
> by anyone else. I have checked its doesn't seem to be related to how
> many recordings are going on. I have seen it recording 3 or even 4
> shows at the same time with out any issues.
>
> It did seem to start some time after I added the USB tuner, I am not
> sure if that's to blame. Is there anyway to tell which tuner a
> particular recording came from?

Sadly, no - it's on the wishlist, though:

"Add the 'cardid' field to the recorded table, so it can be determined which
card(tuner) was used to make a recording. This is useful information for
maintaining _quality-control_ of back ends with multiple cards having
different tuners with different sensitivities, that affect recording
quality. This information only needs to be in the DB not in a UI."

<http://www.mythtv.org/wiki/index.php/Feature_Wishlist_%28Frontend_Addons%29>

That doesn't sound too difficult, so I might take a look at it myself.

Also,

"keep statistics on DVB signal strength so you can see the effective quality
of reception or aerial, and keep track of dropped packet counts for
recordings, allowing people to know if a recording is good before trying to
play it"

<http://www.mythtv.org/wiki/index.php/Feature_Wishlist_%28Backend_Addons%29>

...sounds like a useful feature for these sorts of circumstances.

> It seems to happen on certain multiplxes. The one that carries five
> seems to be the worst effected. However it also seems to happen on the
> one that carries BBC1. The one that carries Channel 4 seems to be
> fine. It screwing up a recording of Spooks was the final straw
> (watching it on iPlayer is just not the same :).

One thing you could do is to try rescanning (or at least doing a recan of
current multiplexes). I anecdotally associated doing so with fixing some
problems I had recording from some channels a while back. My problem was
all-or-nothing, though, so it probably won't help in your situation.

The other thing you could try is using an aerial amplifier. You may just end
up amplifying the noise, but it's cheap enough to be worth giving a try.

> Charlie M

Best Regards,
Alex


More information about the mythtv-users mailing list