Hold on people. Let's understand the issue. Are you all referring to using a Roku TV, and getting pixelation from an OTA (over the air) channel? Or are you referring to using some other app/channel on any Roku device (TV or player) that offers OTA channels?
Of course, the answer for either situation is a lack of signal strength from the OTA station transmitter to your location (Roku TV) or wherever the OTA station is being received and fed into a channel on the Roku.
Digital OTA television is quite different from the old analog broadcasts we used to have. With analog, you could have a very weak signal, but still could have a watchable broadcast. Of course, it might have "snow", or other interference with the clarity of the video/audio, so "watchable" is subjective. With digital broadcasts, you effectively have a perfect picture regardless of signal level, until you reach a point that it simply disappears. This is sometimes called the "cliff effect". Right at the edge of the cliff, you might get some signal, but it's insufficient for a clear image. That is the pixelation you are seeing.
If your pixelation is with a Roku TV watching an OTA station, either the station is having a problem or your antenna isn't receiving a strong enough signal. If the station is having a problem, there's nothing you can do. If it's at your end, you can try re-aiming the antenna (use antennaweb.org to know where to point it), or perhaps a larger antenna is necessary.
If it's happening within a streaming channel on your Roku, the pixelation is not at your end at all. There's nothing you can do to improve the image. It has nothing to do with your WiFi signal. Contact the channel provider and let them know they have a signal issue with the channel. Giving them the specifics about the OTA channel involved will assist them in checking it out.
Dan Roku Stick (3600), Ultra (4640), Ultra (4670), Ultra (4800), Premiere (3920), Insignia 720p Roku TV, Sharp 4K Roku TV, Nvidia Shield, Windows 10 Pro x64 running Serviio and Plex on a wired Gigabit network.
I have the same problem. Using ROKU streamingstick+ with plenty of speed and bandwidth. Samsung smart TV with 4k. Channel is 11 in Atlanta market so should be latest tech. Also on that same channel it reloads and zooms. Other local channels don't seem to do this. Can there be a conflict between the refresh rate on the TV (120) and that on the ROKU (which I think has a maximum of 30 or 60)?