There is a relatively simple way of testing and confirming if an issue is relating to a picture problem or if it is due to reception issues that are unrelated to a TV.
Bad reception may cause issues in sound and picture by creating stuttering or high pitched noises along with pictures being misaligned or very pixelated.
Examples of bad reception can be seen below.
Your TV has a built-in check to determine your DTV signal strength.
To access this on your TV, navigate to:
Menu > More > TV settings > Channels > Manual
This will show signal level and signal quality:
This applies to the following TVs: