Available as an assembled Module and as a DIY project.
This Module is currently available.
Frequency Shifter Model 185 clone
Frequency Shifter Model 185 clone.
La Sesenta y Siete 185 Frequency Shifter shifts frequencies contained in the input signal by an amount equal to the applied carrier frequency . Raised and lowered signals are simultaneously available
https://modularaddict.com/185-frequency-shifter-pcb-panel-la67
These merchants probably sell this module. Huh?