It uses SDR techniques and a combination of AM and FM to achieve polar modulation and generate SSB. He’s provided a fascinating in-depth technical explanation to help understand how it works.

A recent video from [W2AEW] shows how this works and also how AM can be made more efficient by stripping the carrier and one sideband using SSB or single sideband modulation.

The LT5528 is a direct I-Q modulator incorporating a matched pair of double-balanced mixers that form a carrier suppressed, image reject I-Q (In phase and quadrature) modulator. It is intended for ...