700mW FM amp
700mW FM amp
by dare4444 Tue Jan 14, 2020 9:43 pm
https://ibb.co/5BkqsRj
Hi Harry, I came up with this circuit after a few days of work. It's stable and first stage is common base to isolate the input. Output power is around 730mW without a LPF into a 75ohm dummy load. I think the input was less than or around 5mW.
Let me know your thoughts on the design. I am still having trouble designing a proper output matching network. The simple L and C in series matches it pretty well to the dummy load with a final efficiency of 65%.
Update: Amp seemed to be unstable so I added a 100ohm resistor in parallel with base RFC of the final transistor. Output is now 530mW @ 93MHz with 5mW input (about 20dB total amp gain and 57% final efficiency in Class AB mode).
New Update: I removed the final base RFC altogether and base is directly connected to 680ohm + 47ohm biasing resistors. Output is now 380mW @ 93MHz. This is very stable.
Hi Harry, I came up with this circuit after a few days of work. It's stable and first stage is common base to isolate the input. Output power is around 730mW without a LPF into a 75ohm dummy load. I think the input was less than or around 5mW.
Let me know your thoughts on the design. I am still having trouble designing a proper output matching network. The simple L and C in series matches it pretty well to the dummy load with a final efficiency of 65%.
Update: Amp seemed to be unstable so I added a 100ohm resistor in parallel with base RFC of the final transistor. Output is now 530mW @ 93MHz with 5mW input (about 20dB total amp gain and 57% final efficiency in Class AB mode).
New Update: I removed the final base RFC altogether and base is directly connected to 680ohm + 47ohm biasing resistors. Output is now 380mW @ 93MHz. This is very stable.
dare4444- Posts : 427
Join date : 2013-03-19
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