Looking for movie with ham radio father on phone talking to son who tries change the past?

You're likely thinking of the 1985 film "Back to the Future".

Here's why:

* Ham Radio Father: Doc Brown, the eccentric scientist who invents the time machine, uses a ham radio to communicate with his son, Marty McFly.

* Son Trying to Change the Past: Marty travels back in time to 1955 and inadvertently interferes with his parents' meeting, putting his own existence at risk.

While there might be other movies with similar elements, this iconic film is the most fitting description.