Hi,
So, I'm learning emitter follower by building a circuit that is described in Learning the Art of Electronic book in the Lab 3 chapter. In the book, there's an emitter follower circuit to demonstrate the clipping effect and how to remedy it. The circuit is attached below. However, there's a note in the book that a base resistor is needed to omit any oscillation. I was very skeptical when I read that note, so I tried to make the circuit without the base resistor.
At first, the circuit was fine. No noise was found. However, it started to pickup noise randomly. Sometimes it was free from noise, the other time, the noise came. I also tried to reduce the noise using the suggestion from the book, such as shortening the wires, and putting some bypass capacitors. However, I found out that the noise came when the output wires (the red and black wire with alligator clips) of the signal generator were moved apart. You can see the picture in the attachment.
For the cause, I suspect that when I moved the wires apart, the wires formed some kind of antenna and it picked up radio waves because when I zoomed in, it had 50MHz sine wave with 1.5 max amplitude in the noise. I researched that 50MHz band is used for amateur radio. However, is my guess correct? Is there a way to confirm it?
Also, when I put the resistor into the base, that phenomena didn't happen. What I don't understand is, how does the resistor suppress the noise?