I bought a variable attenuator like the one in the Keith_Beddoe's linked picture. Turning the dial on this my BT YouView box reports the signal strength is varied between 50 and 100%. The Signal Quality is always reported as 100%. I tried viewing TV at ~50%, 60%, 70%, 80%, 90%, 95% but could not discern any noticeable change in picture quality on any setting. The picture quality on the LG TV using the Freeview aerial is better than the BT YouView through HDMI. I don't see any settings on the LG to adjust the HDMI inputs other than simplelink. The picture looks good via BT YouView and I would have been happy with it had I not seen the superior Freeview quality.
I have exactly the same problem, I have samsung 4K TV and a BT Ultra box (on 10 bit setting) and freeview is much better picture quality without doubt. If input aerial is from same source then only explanation is Samsung freeview picture process is better quality than BT Ultra box. Also notice that Sky sports main event HD picture quality is much better than BT UHD picture quality, surely this should not be the case.
Does anyone have access to a Sky Q box and can the same be said of the UHD picture quality v HD quality or is there a real difference?
The difference in quality you're seeing is real, and not imaginary.
The phenomena isn't just limited to BT 4K boxes, for example, some Sky Q owners report similar, as do Virgin customers.
So what is causing it?
When you watch a Freeview HD channel on a 4K box, such as the BT Ultra 4K box, the box is internally up-scaling an HD image from Freeview in order to output a 4K image to your TV.
When you watch a Freeview channel on your TV, it is your TV that is doing the up-scaling, converting the HD image to map correctly to the TV's native 4K resolution.
What you are seeing is a difference in up-scaling performance between the chip in your BT box, or Sky Q box, etc. to the chip in your TV.
Most modern TV's like Sony's, Samsung's, LG's, etc... have very advanced chips for up-scaling and cleaning up images, much more advanced than the chips fitted to most set-top boxes, which are based on technology from a few years ago and are built to be cheap...
That is what you are seeing...
This why I set my PVR boxes to send the signal to the TV in native mode and allow the TV to do all the upscaling.
Thanks, all sounds logical. I have my BT ultra box set to output my picture to my TV HDMI display using the following settings - UHD 50fps 10bit. Are you advising that I set it 720p, 1080i, 1080p, UHD 50fps 8 bit or the above to enable the TV tuner to do the job? Your help and advice would be appreciated.
I have always found the HD picture from the 4K box very soft, no matter what setting you select.
Mine is on 1080i usually, as that is the normal broadcast standard and my LG OLED upscales everything with no way to turn it off. The streamed HD channels I believe are 1080p but the difference between the two is really splitting hairs.
I don't have enough speed for the 4K channel. I have access to 3 BT boxes, the zapper, the standard box and the 4K version. Picture quality on the zapper and standard box are comparable, the 4K is the worst.
I also have a Humax retail version and it is better picture quality than all of the BT versions.
Thanks. My speed 70Mbs so 4K looks OK, but OK is not what I expect from a UHD picture.
I actually often watch sport on my Apple TV app rather than the BT TV box as the picture quality is far superior.