conjunctions - When do I need to have a preposition before whether?

I often see prepositions that come before whether and I feel that most of the time these prepositions are unnecessary.

I'm confused as to whether a preposition is required before whether.

I haven't decided on whether to put a preposition before whether.

I don't know about whether a preposition is required before whether.

The times where I feel a preposition is preferred involve a noun coming before whether.

There's no news as to whether Jane will show up to today's meeting.

We haven't received an update on whether the party will arrive on time.

Is a preposition ever required before whether? If so, what are the circumstances where one would have to use a preposition before whether?