Problems with VHF amplifier

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oasis4355

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Hi all,

I came out with a class C vhf amplifier for the last stage of my transmitter, referring to the image that i've upload, it suppose to have a 20dBm gain at 100MHz in S-param simulation with ADS.

However, when I've input a 100Mhz signal at -10dBm into the amplifier using a signal generator, not only it doesn't amplify the signal, it somehow makes my signal into -20dBm, when i check with a spectrum analyzer

What seems to be the problem? I've check the circuit on the PCB board, everything seems correct.

Please advice,

Thanks in advance





 

i think there is an error in base bias point , u but there about 9 v through the 100 K , which mean that ur transistor in sat , not in cuttof
the class C amp , ur bias should be less than 0.7 , so when the input voltage incrase this and make the mp in active mode

u need to study class C amp concept

khouly
 

Hi,

Thanks for the info. But the circuit is working fine in simulation. Here's the image.



 

If I understand your minimal information, you have actually built this amplifier and are driving it with-20 dBm? Well, try driving it with +10 dBm and see if it works.

Also, I agree with Khouly, you seem to have the base bias screwed up. Try a 10 K to ground and get rid of that 100K pull up.
 

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