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what transistor to use for HF application

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dbtcstudent

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hi! how can i know what transistor to use for RF application specifically 13.56MHz frequency? what parameter in the specification sheet states wheteher it would be useful?

can i possibly use a transistor designed for VHF/UHF application for HF application?

thank you!
 

Yes u can use the devices of VHF/UHF. But UHF devides might be more expensive. Looking at ur application any device of ft upto 200Mhz. will be ok.
 

For this frequency range you can use almost any type of trnsistors available nowadays.
I think the best parameter to check is Ft.
A transistor should behave as an ideal transistor up to frequencies as high as Ft/10.
Most of the small signal bipolar transistors available today have Ft better than 300MHz (including the ones for audio applications and switching!!!!)
So, I think any transistor should satisfy your application. Shouse a high beta one like BF494 or even BC547 and it will work very well....
Greetings to all you
S.
 

thank you very much! it's nice to have people like you... :)
 

sinatra, you mentioned small signal...i need to use the transistor to have an amplifier output power of 4W. can a small signal amplifier do the job?

is there anyone out there that can help me distinguish the distinction between small signal and large signal parameters/amplifiers?

thank you again.
 

Hey, you discovered another key transistor spec: the bias current. The transition frequency ft is not a fixed number, it depends on the ce bias current. To lower this DC current, the lower the ft. So to get the same ft with a higher current setting, it is better to use two transistors in parallel. Or to make it easy for us: let the manufacturers do this! Just buy a transistor with a bigger die! You can see this in the datasheet by looking at the maximum current and recommended bias current.

Power amplifiers need high output power. As the voltage rail is limited, extra power needs to be drawn from higher current settings.
 

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