Here is a circuit of amplifier of a wireless receiver.


The carrier frequency is 27MHz or 303MHz.
The data tones may be 500Hz to 2kHz, Sq. waves.
The signal amplitude is 2mV.
The quality of the output signal is not very important as I just need to read the frequency of the signal.

I used this circuit but output does not show any amplification. Here is the image of the signal I read on my scope:


The Y-axis is set at 2mV/div.
The same signal with x5 gain


The input signal and the output signal is almost the same.

Shall appreciate if someone would help in improving the circuit.

 

Neither transistor is biased properly. Where do you think the Q point is on the DC load line? What gain would you expect out of a 2N3904 at 300 MHz?

 

Neither transistor is biased properly. Where do you think the Q point is on the DC load line? What gain would you expect out of a 2N3904 at 300 MHz?

I am just a hobbyist, not an expert. I replicated the circuit I found on internet (just changed the transistor 2N2222A to 2N3904). I requested suggestions to improve the circuit.

 

At frequencies like that things like stray capacitance and the values of your resistors have a huge effect on bandwidth. According to the Fairchild 2N3904 datasheet the output capacitance is 4 pf. Combine that with your 33k load resistor and you have a low pass filter on the output that starts rolling off at 1.2 MHz.

There are other effects to consider as well, but that one best illustrates what you are up against.

If you drop the frequency to, for example, 50 kHz you should see a considerable improvement in performance.

The best way to learn about applications of transistors is just what you are doing -reading about them and working on circuits.

Below are a couple of resources that might help you.

FR Power Amplifiers

Designing and Building RF Power Amplifiers Part 1
Designing and Building RF Power Amplifiers Part 2

 

Thank you Dick for sharing the idea about 'LowPass Filter' in such amplifier circuit. This seems simple and I am familier with RC, LC filters too, but I never got any chance to calculate in that way. So just replacing the 33k resistor with 100nH (5mm diameter, 5 turns) coil gives 251MHz cutoff frequency. I used to think they just use inductor at the collector to get higher peak to peak voltage swing (RF wave) than Vcc.