Saturday, November 10, 2018

JFET mixer

First a look at the schematic.
It is straight forward. Feed a signal to the gate another to the source and draw the output from the drain. Seems simple enough. The circuit is a bit to simple but we will see.
The display is the top of L1, L4 and L6. The inputs are 2.0 MHz and 2.1 MHz One of which is modulated with a 1 KHz tone.The green is the 100 KHz output. You can see the inputs are a higher frequency but the 1 KHz tone is lost because the sweep is to fast.
The input transformer is step up. I moved the probe to L2 and the input is a phasing is a little easier to see.As the red and blue go in phase the read peaks.
I changed the sweep to show the 1 KHz modulation better. As you can see the orange signal is constant in amplitude. The green is the modulated signal and the pink (difference signal) is carrying the signal too.
Next step will be to wind 3 cores and gather some test equipment and probes. First I should point out the mods I made to the original circuit. I did not put the resistor in the drain circuit. In the build I may use it. I put the bypass below the tank in the drain circuit. I wanted to bypass the tank with the high frequency signals. I used a different JFET simple because I don't have any MPF102.
Anyhoo, time for a build.

No comments:

Post a Comment