Piper J3 Cub pilot reported while on short final; another aircraft entered the runway for departure resulting in the pilot taking evasive action to avoid a collision with the departing aircraft. After landing; the pilot was informed their radio was not transmitting in a readable manner.

Narrative

I was on a local flight in my Piper J3 Cub; maybe 25 minutes. As I was returning to the airport; I noticed one of the flight school airplanes holding short of runway XX. Outside of the traffic pattern; I did two 360° circles to give the 150 a chance to take off and see if he was going to stay in the pattern. Upon completion of my circles; he was still at the hold short point; so I decided to enter the pattern for landing. I made radio calls so he would be aware of my position. As I was on final for a short approach; I noticed the 150 leave the hold short point and begin taxing onto the runway. I radioed for him to stop his roll as I was on extremely short final about to land. There was no response to my call; he continued his roll; so I side stepped to the right of the runway and initiated a go around. I kept the 150 off of my left wing in sight; because it was clear he did not see me. A pilot on the ground made a radio call to the 150 asking if he had the Cub in sight. The pilot in the 150 made radio calls about his own position; but did not answer any radio calls directed his way from the pilot on the ground until he was exiting the pattern. Once I knew I was safely away from the 150; I re-entered a normal traffic pattern and landed on XX without issue.Once I was stopped on the ground; the other pilot on the ground told me he could not hear my radio calls. He could hear that a transmission was being made; but words were unintelligible. Being that a Cub does not have an electrical system; I use a handheld radio attached to a headset. This sometimes does not allow for the best radio communications. We have since corrected the issue and the radio should function much better now.I spoke with the other pilot in the 150 when he returned. He was a student pilot on a solo cross country. He admitted his mistake saying that since he did not hear any radio calls; he assumed the area was clear and did not look down final before he rolled onto the runway. We discussed the dangers of that and it seemed like he understood that radios are not sufficient forms of collision avoidance; especially in airspace where radios are not required. See and avoid with visual scanning is king.After our conversation; the student talked with his instructor; and it seemed the instructor was of the mindset that radios need to be used over visual scanning. This would be a shortcoming in instructor emphasis areas; because not all airplanes are built with radios. I believe more emphasis on see and avoid and always looking multiple times while rolling onto a runway in instructor training could have help avoid this issue. New instructors need to be properly taught about effective scanning techniques before making any turns in the pattern or entering a runway to avoid mid air collisions. Radios are too heavily relied upon for traffic avoidance; and a shift in the culture of traffic avoidance techniques needs to happen.There are multiple airplanes at this airport that do not have radios; so it is not a new thing for this student or instructor to interact with an airplane not talking on the radio in the pattern.