Techniques for calculating the system characteristic of the adaptive filtering used for equalization and echo-suppression in a digital communications receiver, such as one used for receiving over-the-air broadcast digital television signal, are described. Said guiding mechanism includes a manually operated guiding control. A top plate adjustably and slidably engages the back plate in order to exert tension on a string. The chopper devices are conductively coupled with both the traction bus and the auxiliary bus to control conduction of the first voltage on the traction bus to the auxiliary bus as the second voltage using first and second duty cycles. This method makes it possible for a pilot to view weather imagery overlaid on an electronically displayed map without having to switch back and forth between overlay and underlying map to see detail information when zooming in or out of the map.