Pixellation only at top of screen

[Pixelz]

Receiving Freeview terrestrial broadcasts in the UK,
I'm seeing pixellation at the top of the screen, only extending over about 10% of the 1080 horizontal lines, and only on the LOC multiplex.
In my case this is UHF35 or 586MHz from Crystal Palace, including Sony Classic Movies, London Live and Ideal Extra.

Media Centre tuner is a TBS6285 quad DVB-T and the graphics card is an AMD Radeon HD6450.
I can workaround the problem by using zoom 2 to crop the top and bottom of the picture.
Interestingly, my Sony TV tuner is not affected by this pixellation.

Just wondering if anyone else in the UK has experienced this problem.

[CyberSimian]

I'm seeing pixellation at the top of the screen, only extending over about 10% of the 1080 horizontal lines, and only on the LOC multiplex. In my case this is UHF35 or 586MHz from Crystal Palace, including Sony Classic Movies, London Live and Ideal Extra.

I receive Freeview from the Rowridge transmitter (Isle of Wight), using a TBS 6264 tuner card, plus a Pinnacle 2000i tuner card. Rowridge transmits 9 MUXes:

• 3 MUXes at 200 kWatt power
• 3 MUXes at 50 kWatt power
• 3 MUXes at 20 kWatt power

Because I use a loft aerial instead of a rooftop aerial, I can receive the 200 kW and 50 kW MUXes without problem on the TBS 6284, but the 20 kW MUXes are marginal and not of watchable quality, so I have deleted them from my channel lineup. This includes "Sony Classic Movies".

The local MUX, and the one or two "temporary" DVB-T2 MUXes are broadcast at low power (20 kW in my case), and at the higher end of the frequency range. Both of these properties make them more difficult to receive. It might be worthwhile checking one of the Freeview web sites for transmitter information to see what power your transmitter is using for the different MUXes.

I suspect that your problem is caused by a marginal signal, which might be improved if you employed an aerial installer to fit a better aerial system. But is it worth it for the MUXes that are of marginal signal quality? In my case I decided that it was not.

TVs have tuners that are more sensitive than PC tuner cards, and my Sony TV can receive the 20 kW MUXes at watchable quality most of the time (even if not perfect). In contrast, my Pinnacle tuner card is less sensitive than the TBS 6284, and can receive only the 200 kW MUXes -- the 50 kW and 20 kW MUXes are nowhere to be seen.

-- from CyberSimian in the UK

[Pixelz]

Thanks for your detailed and helpful reply. LOC is the weakest mux from Crystal Palace on 586 MHz at only 20kw, but media centre is reporting signal quality of 100% from my masthead amp. You could still be right but it's confusing me that the pixellation is only ever seen at the top of the screen.

Also, if a channel on this mux shows a movie letter boxed with black bars top and bottom then there's no problem. This gave me the idea to use zoom 2 mode on affected programmes which also helps.
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I'm trying to find out if this mux uses a different encoder that may be incompatible with my setup, and I'll post again if I find anything.