This question would have brought a better answer over on the Radio Forum.
These condensers have nothing to do with static or radio interference. These terms generally refer to something being picked up by the antenna.
If you have ever looked at a motor or generator or alternator in a dimly lit garage or at night, you will have noticed sparks flying off the brushes. This is electrical NOISE. If your generator is closed up, look through the vent holes on your hand drill.
An oscilloscope is a voltmeter that shows voltage over a short period of time. 12 volts from a battery is just a straight line. 12 volts from a generator looks like hacksaw blade teeth, only not as regular. If you rev the engine up, the teeth will pull back closer together. "If you get a buzzing noise in your radio" as wrenchbender said, that speeds up with the engine, you will most likely need a condenser on the generator and/or the coil to filter out the noise.
That AC-Ducey stuff has very little to do with radio noise, but you guys forgot half of the story. On the radio forum, someone just ask about vibrators the other day. With an old truck with an old tube radio and a modern alternator it works like this. The alternator produces AC, the rectifier converts it to DC, the vibrator converts it back to AC, a transformer kicks that AC up to at least 90V and a rectifier converts it back to DC.
So what you really have is AC-DC-AC-DC and then you get your Merle Haggard
