A mixer circuit includes a first switching mixer with a first desired signal input, a first switching signal input, and a first output, a second switching mixer, and a third switching mixer with corresponding desired signal inputs, switching signal inputs, and outputs. Support elements for accessories are fastened to said accessory adapter. The interleaver of size N=n*m is defined by dividing the N possible address in the interleaver into n subsets. The open end is securely attached to the opening in the wall for receiving the mail containers into the tube, while preventing air circulation outside the building from entering the opening. The shade system obstructs unnecessary light that does not contribute to the exposure.