In SH3 there are more or less 18 different radar equipments. Here there are a lot of informations on several radar types used during WW2 on US warships:
http://hnsa.org/doc/radar/index.htm
Radar rotation was manually tuned by the operator using a knob on the radar instrument panel. So we can just decide a general rotation speed...
I found the Type 268 was rotating at 22rpm, so almost 1 complete turn in 3 seconds.