I have found a circuit that does AM modulation with a JFET transistor (2N5485). I modified it slightly and ended up with the circuit below. A sample output is also given.
I used Microcap 12 for the simulation.
For my message signal I used an AC amplitude of 0.5 V and I also gave a DC bias of -1.7 V to the gate of the JFET. The frequency of the AC is 500 Hz. For the carrier I used a 40 kHz AC signal of 0.5 V amplitude.
I noticed that if I play a little with the DC bias (close to the threshold voltage of -1.71 V) it changes the output noticeably and hence the amplitude modulation.
I also noticed that the message signal in red is not exactly the envelope of the blue (modulated output).
Is there anything I can change to have better modulation?
I am new in this field of electronics so I am sorry for anything I might have misunderstood about the whole process.
AM output (blue) and message signal (red):