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

[Tobias Hilbert]

Am Montag, 15. Dezember 2008 schrieb Charles Mason:
> Hi All,
>
> I have been using MythTV for a few years now. My backend currently has
> two tuners a PCI Nova-T Hauppauge card and a USB DVB-T from hauppauge.
> I use both to receive Freeview from a large roof top aerial. One of
> the multiplexes has always been a bit patchy and so have never really
> bothered about it, however the rest seem really good & reliable.
>
> We live out in the country on the side of a hill and have a very clear
> line of site north towards Emley Moor. This is a fairly powerful
> transmitter but its a long way away. We can get two other signals from
> Sutton Coalfield and one near Nottingham (the hill virtually kills
> that one).
>
> 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.
>
> 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?
>
> 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 :).
>
> The only other possibility is that its my NAS. All the recordings are
> stored on my FreeBSD based NAS which is on a 100 meg wired network
> with the backend. I suppose it could be related to that some how. The
> recordings are stored in the ZFS equivalent of RAID 5 so I should get
> errors if there was a disk problem. Although I suppose if the NFS
> packets never make it to the NAS I wouldn't see ZFS errors. All the
> other machines on the network access the NAS and MythTV server via
> WiFi so I can't see how any other use of the NAS could saturate it
> stopping the MythTV server accessing it.
>
> Does anyone have any suggestions to try and track this down. Its been
> happening for months and affects about 35% of the recordings so I
> really want to solve it.

You don't have by any chance a wireless phone using the DECT standard.
Those phones are known to interfere with the dvb-t signal if you use cheap 
wireing/cable or indoor antennas.

Tobi
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