The plug-in concept was inspired by the National HRO-series receivers. Most multi-band receivers use a complicated rotary bandswitch, with lots of wires coming and going! Once installed, those things are impossible to fix or modify. My home-brew experience taught me that changes and modifications are always necessary. This project had to be easy to modify. The plug-in tuning units make it easier to work on. Also, each of the major sub-assemblies are on connectors, so they can be removed for changes. Even the front panel can be removed, and there is one big connector for everything on the panel.