Sorry I was wrong about the noise figure at 100Mhz for the mosfet BF981.
It has to be 0.7dB instead of 1.7dB!

It can still better with the BF998, to get an impress of the scheme try the
following link http://lea.hamradio.si/~s53ww/4xbf998/4xbf998.htm

I think it can be reproducible whitin small variations.