This single diode mixer circuit adds the RF and local oscillator signals before applying them to the input of a diode.
It has been designed for direct conversion use with the mixed output signal developed across the 10k resistor. Although in this test circuit, the difference signal is 470 Khz. (This is easier to see on the app).
The D.C. power supply allows a bias current to be passed through the diode. This moves its operating point "up" its characteristic curve. This means that the signals are not relied on to switch the diode on. Thereby, smaller amplitude signals can be mixed. (That's my theory anyway!)
The load line technique can be used to find the operating point of the diode.
