Try a new HDMI cable and/or a different HDMI socket on the TV.

Seperate aerial cabling from the HDMI cabling.

Ideally replace coax interconnects made from WF100 (satellite grade double screened) cable, terminated using screw on f connectors and F to Belling Lee adaptors where needed.

Poorly Screened HDMI cables generate radio frequency signals in the UHF band. Easily picked by cheap poor quality coax interconnects.

Joe1 – 5 mins ago  » 

Thanks Graham,

I tried a different cable, neither were very cheap ones

[bought specifically and both shielded]

and also tried both in different HDMI sockets.

The cabling is already as spaced as possible.

There was no change when I tried this.

By coax interconnects, do you mean the connectors as found on the end of the main aerial cable ?

If so, there is only one of those on the arial itself and it is intact.

Just the arial into the box, then HDMI into the TV – no other devices attached or even nearby.

It appears to affect some channels more than others, Sky News & Pick for example, but I have noticed it briefly on an HD channel also….

so I can therefore rule out the “Muxes” shared channels presumably ?

Attached is a snapshot of an example of the problem I can see on the screen.

I don’t know if this looks like something that is a known problem.

[attachment=77847,1406]

The more expensive cables are often much worse than a cheaper one. Try a 2M from Home bargains.

Graham, could the vertical distortion be something like a radar pulse or RF interference. I recall seeing something like it in the past but it reoccurred at regular intervals.