hello my friends i searched a lot in the internet and i couldn't find my answer.could you tell me what is exactly FT do in transistor? what are the formula that join ft to another transistor elements for designing an oscillator or mixer? if good book tell me more i will appreciate you. i read the wikipeida before.but i asked many people about ft to choosing a transistor for desire job.for example if i want to create a collpits oscillator with 100Mhz frequency what transistor should i choose?what is the formula according the ft of transistor and my frequency? could you help me ? its not very important to tell me in English.please tell me with your fresh language its important to me to understand and know about electronics in RF environment as you see in many oscillator with frequency between 90-108 Mhz they use c945 with 150 ft,how it works fine? does we have an equation that explain the formula between Voltage Gain and ft in colpitts oscillators? because i asked somebody else but tell me that "current gain * BW product = fT " but if i use emitter-common that Current gain is approximately 100 and for oscillate my circuit in 100Mhz i shoud use transistor with ft 10Ghz?!!! Does any books tell me moe about designing collpits oscillator with all steps(such as choosing transistor , Capacitor , ....)? theory and experimental?