whistle register

I'm trying to learn whistle register. I've hears all the safe practice crap. I can make a high pitch whistle but Its not loud. I want to know how to control volume of it/power. My friend can do it and the only time I got it the way I know it was wrong because I went into large cough. That's why I'm doing it this way. Also I got it very well when I got bronchitis. I had more control and everything until my voice returned I forgot everything.

I can get high pitch for long periods. But I don't get whisper talk or croak sounds on the way to it like friend.

No thank you.

Ok that did sound wrong...

Google it a bit and you will be safe!