Ebay finds: NOS super vintage 1N263 mixer diodes, 60 of them !

[Soundfactory]

In the 80's we did experiments in the 10 GHz range. So a similar diode has been screwed behind a horn antenna in a waveguide. Behind it was a GUNN diode installed. Thus one had an oscillator, which served as a transmitter and at the same time as a mixed oscillator. As IF, we have chosen 100 MHz to be able to demodulate broadband FM with a commercially available FM radio. 73 DE DL1LAJ

[lawz_]

Useful for making field strength meters or near-field monitor receivers for the microwave bands. Just add a high-gain audio amplifier or millivoltmeter.

[TerryMcKean]

Yep.. definitely some beautiful-looking diodes... one could use 4 of those and build an awesome crystal-set... one with a, as ElectroBOOM says, a "FUUULL BRIDGE RECTIFIER!!" as the detector. :-)