@60hz When you send at 30Hz how are you refresing.
I would expect 40Hz....... something like this.......
David.
If you can get the RPI to use a virtual driver for the cheap dongle that would be good..... and worth a tutorial.
ALSO.....!!!! maybe you need to terminate the DMX line....... stop reflections on the cable....!
ALSO.....!!!! maybe a powered hub for the USB would help.