Factual error: A ham radio requires the person to hold down the button while talking. Numerous times in the movie they are talking without pushing the button.
Suggested correction: This is actually subtly addressed in the film. The magic which allows the radio to work across time also allows the two men to speak without pressing the button. There is a moment where Frank wonders what is going on with the radio and presses the button a few times to talk but then notices that he doesn't have to press the button to be heard.
If that was true, then it wouldn't make sense for them to continue to show Frank and John hitting the squawk bar throughout the film.
That is a separate issue. The mistake entry states that you need to hold the button to talk on a ham radio, which is true, but the magic ham radio in the film doesn't require it. If the actors continue to occasionally press the button that could be considered a character mistake but it could also simply be a force of habit by the characters.
Factual error: When Shep and his partner are looking for Frank on the docks in 1969, the camera pans to the left and we see a flash of the (completed) World Trade Center buildings just before the cameraman catches his error. In 1969 construction had only just begun on the towers.
Factual error: The radio used in the film is a Heathkit SB-301 receiver only, and is, in reality, incapable of transmitting.
Factual error: In the year 1969 Dennis Quaid reaches into a pile of Albums (vinyl) to play the "King". One of the albums in that pile is "Elvis In Concert" which was not released until 1977. (00:07:40)
Factual error: When the first change in the past takes place, the victims go from three to ten. One of the victims is John's mother. He would never be allowed to be part of an investigation with his mother as a victim.