Try moving the end of the spring up and down repeatedly. There will be noticeable radiation in the direction perpendicular to the oscillating motion.

This effect is detailed in chapter 34 of the Feynman Lectures on Physics; please read that first. To observe this effect, you will need to move the end of the spring around in a circle, that has a diameter of about 1/3 of the simulation's height. You will need to move quite fast, though not too fast. Experimentation works best here. The goal is to get the charge moving in a circle (any roughly circular path will work). Then, there will be noticeable sharp pulses in the electric field, traveling outward in a spiral pattern.

This effect is detailed in chapter 34 of the Feynman Lectures on Physics; please read that first. The Bremsstrahlung (or braking radiation) effect can be observed by speeding the charge up so that it approaches the speed of light. This can be done by dragging the charge to one corner of the screen and then very quickly moving the end of the spring to the opposite corner. This way, the charge will approach the speed of light. This is visible when the waves generated by the charge do not travel forward much faster than the charge itself. When the charge slows down, it "spits" radiation forward in a wave with a very large amplitude.

This effect is detailed in chapter 34 of the Feynman Lectures on Physics; please read that first. You can observe the Doppler effect by moving the charge to one end of the screen, then moving your mouse in a sinusoidal wave; oscillating up and down while simultaneously moving forward. You'll have to experiment a bit to find the right frequency and amplitude, but after that, you can observe waves with shorter wavelength in the direction of motion, and waves with longer wavelength in the opposite direction. Be careful: you will need to move the mouse forward relatively slowly so the charge does not approach the speed of light.