I bought a BJT BF200 as a high frequency transistor but I found it has 4 terminals not only 3 like that used in conventional transistors. the fourth terminal for the case and I am using it in FM receiver so where should I connect this fourth terminal? do I leave it unconnected or connect it to collector ?
I would expect that the purpose of the 4th terminal is explained ín the datasheet. Some old style metal can packages have a shield terminal which should be connected to circuit ground.
Yes but I knew it is for the metal packages but I found that in other BJT transistors collector was connected to directly the package by manufacturer without a fourth terminal especially power transistors.
The BF200 is a very old silicon RF transistor and has not been made for many years. The datasheet shows its 4 pins and one is its metal case. I would think that there will be some capacitance from the chip to the metal case.