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modulator circuit

xpower

Apr 1, 2012
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hi guys.
am new here and this is my first thread :) hopefully am posting in the correct section :D

Ive been trying to understand the circuit of a cheep Chinese wireless door bill. Ive done the circuit in the Proteus simulator. but i couldn't get the oscillation at 315MHz. the circuit consists of encoder that produce pulses and oscillator to modulate the pulses. but in the simulator i couldnt get any oscillation hence couldn't guess if it is FM or AM.
C9018 transistors were used in the circuit, but i used 2n2222a cuz the first is not available in the simulator. please help
the circuit is attached.
 

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Harald Kapp

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Try to find a high frequency transistor in your simulator. The C9018 has a transition frequency of 800 MHz (typ), whereas the 2N2222a has only 300 MHz. Since the gain of a transistor is 1 at the transition frequency and falls below unity at frequencies higher than the transition frequency, your circuit can't oscillate.


Harald
 

GonzoEngineer

Dec 2, 2011
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Try to find a high frequency transistor in your simulator. The C9018 has a transition frequency of 800 MHz (typ), whereas the 2N2222a has only 300 MHz. Since the gain of a transistor is 1 at the transition frequency and falls below unity at frequencies higher than the transition frequency, your circuit can't oscillate.


Harald

Excellent!:D
 

xpower

Apr 1, 2012
4
Joined
Apr 1, 2012
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4
Try to find a high frequency transistor in your simulator. The C9018 has a transition frequency of 800 MHz (typ), whereas the 2N2222a has only 300 MHz. Since the gain of a transistor is 1 at the transition frequency and falls below unity at frequencies higher than the transition frequency, your circuit can't oscillate.


Harald

thanks Harlad :) but Ive modified the circuit to oscillate at 30MHz then ended up with the same result. it seems that this simulator has a bug or shortage. according to my understanding, the circuit should oscillate on each high pulse from the encoder and this is an AM modulation. any idea how can i increase the range. ive added one stage (attached) but doesnt work. :mad: any clue?
 

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Harald Kapp

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I'm not very versed in HF technology. Could it be that some of the inductors should be coupled?

Harald
 
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