This is a standard type of diode ring modulator. The design in this case came from the Magnificent antipodean - vk3ye. However, he is not the originator of this circuit at all.
In his version, he uses signal diodes. These are not necessarily balanced. And so, it was necessary for him to place capacitors to offset the AC differential imbalance.
This sucks, so this version uses Schottky diodes, these are far more balanced and do not require any interference with extraneous component s such as silly little capacitors and trimming capacitors.
They also have a volt drop of 0.4V instead of silicon which is 0.7V
