I'm trying to design a small amplifier for AM signals to use before the usual diode-C-R detection (the reception in my area is very poor). I devised a QUCS simulation as below:
The diode and detection circuit is shorted or deactivated because I wanted to analyze first just the transistor output.The DC simulation shows approx the values I calculated for the biasing (1 mA quiscent current, 0,7V bias on the base and 4,5V on the collector) but when I run the AC simulation I get very strange results: [![Simulation results][2]][2]
Up left is Ve and Vc, up right input (measured at the "antenna") and output (measured at the 2kOhm resistor), low left Vb (base voltage) and low right the input.
I appreciate inputs on how to solve the problem as well as how to design a regenerative feedback for the circuit.
UPDATE: further experimentation made me realize that the antenna can't be floating, it has to be connected to ground. Point is: if I connect it through a capacitor (let's call it stray capacitance) the output gets smaller depending on the size of the capacitor (the bigger the smaller the reduction). If it's tied directly (or the "stray" capacitor is big enough) the input gets correctly amplified but the "positive" part gets squished (negative feedback?):
Can anybody help?