2250 rpm = 37.5 rev/second, so the blade passing frequency is indeed 75 hz.
And one side of the GS is modulated at 90 hz, the other at 150 hz.
I'm not sure what to make of this though: Why should the Tobago be unique in this restriction? It should apply to any SE aircraft with the GS antenna behind a 2-bladed prop arc.
(also for a 3-blade prop at 1500 rpm, for that matter...)
