DX Bases Primary and Secondary Mode
If you are using two or more DX bases in a single space, you run the risk of having RF interference between the two units. By using the Primary and Secondary switch on the back of the base, you are telling the units which base is the Primary and which is the Secondary in order to reduce the chances of RF interference.
This feature is available on the following models:DX-121, DX-100, DX-200, DX-210, MB-300ES and MB-300.
Even though the DX-410 has a primary and secondary switch, it is currently not operational. With that said, the DX-410 has a loss packet concealment feature which reduces the amount of pops and clicks when dealing with RF interference.
Later models should have this feature enabled.