The Opera Cake from Great Scott Gadgets is an antenna switch intended for HackRF One. It is a double four-way antenna switch, i.e. a pair of single-pole four-throw (SP4T) switches. The two parts, or banks as they are called, can be used in parallel as a DP4T switch or in series (sort of) as an SP8T switch. Multiple boards can be stacked on top of each other to create more complex configurations.