Early last month we released a new broadcast AM high pass filter product. The goal of the filter is to block out extremely strong broadcast AM signals (and other problematic LF/MF signals) in order to prevent an SDR from overloading. This is especially needed if you live close to AM towers.
Over on the Utility DX Forum files section, reviewer D. B. Gain has written an excellent review of our broadcast AM high pass filter (pdf), also explaining why and in what situations it might be needed. In the review he explains how broadcast AM propagation works, and how it can change from day to night. He also explains how devices with diode switches (used for switching RF circuits such as filter in and out electronically) can easily overload and contribute to IMD within the switches themselves. This is why a filter without any diode switches in front of it is usually the best solution for reducing strong RF energies.
In the review he then goes on to test the filter, showing some screenshots of the reduction is AM signal strength.