Hello,
I work on an exercise I made up for myself and I need some help. I want to build a small RF receiver with a central frequency of 50MHz.
I made a model of the antenna. I put a band pass filter after it. Both are centered around 50MHz. I want to amplify the received sine with a 7V voltage peak to peak ('Vpp').

Here is my problem:
Theory tells us that if we put several amplifiers one after the other, the total amplification is the product of each individual gain.
However, when I try to put an other amplifier after the 2 first I designed, 'Vpp' stabilizes at around 13mv, no matter how many amplifiers I put.
I tried to match the input and output impedance of my amplifier structures but even there, 'Vpp' stabilizes at 13mv.

Could do you tell me what I do wrong or explain me how I can improve the design?

Thanks.

 

Your first amplifier has a gain of just under 2, and the second has a gain of 1 (at most, it will be less.)

Bypass the emitter resistors with a 1nF capacitor and it will go way up. Also, redo your early stages with higher collector resistors, these are way too low and limit the gain.

 

For RF amplifiers, a choke in place of the collector resistor also gives higher gain.