[nynyny7]

When I had my "I want to build my own SDR" phase ;) ca. 15 years ago, I also used analog switches as a switching mixer - with a PLL running at 4x the desired frequency so I could utilize dividers to get nice 0°, 90°, 180°, 270° LO signals for IQ mixing. Brings back memories...

[cardiffspaceman]

In the 70's the company I worked for made a receiver for fixed frequencies within 10KHz-13KHz. The architecture roughly was discrete time analog, and an analog switch was available that took a digital selection and routed the indicated analog input to the analog output. That block was used to control the sampling for a filter by cycling through the selections. The rest of the design was over my head in those days, since I was the software guy and the software wasn't controlling that.

[bobowzki]

This is called a Tayloe Quadrature Product Detector [1].

1: http://www.norcalqrp.org/files/Tayloe_mixer_x3a.pdf