Thread: RF Interference

I have been working on my TM, so I thought I would make this short video so someone might relate to what is going on with pwm as related to noise and speed of the TM.
You will see the noise spikes near the end of the video. I did some rough calculations of the noise frequencies present. The noise ranged between 1 megahertz down to 100 kilohertz. These noise frequencies fall in the band of the sonar transducer frequencies. (RF). That is why you see it on the screen. This is just a show and tell and does not cover all the noise sources of RF.



Hope it make sense to someone.




Wanted to add that the fundamental frequency of this PWM is 20Hz. So, what you see is a 20Hz modified square wave. When you run wide open, the bottom line goes straight, meaning a solid ground is supplied through the FET to the negative side brush of the motor so there would be no pulses, therefore no noise at WOT (kinda). The reason the pulse fundamental frequency is so low (20 Hz) is because at higher pulsed frequencies, you can actually hear the motor squeal like a pig. When you hear that "click" everytime you hit the foot switch, well, that is a 50 amp relay operating which places 12/24v to the positive motor brush. This is a coasting relay which prevents regenerative braking. In other words, the motor coasts to a stop instead of stopping suddenly. Electric choo choo trains use regenerative braking to slow down. Disc brakes don't work too good on choo choos.