780 khz. Bill O'Reilly vs. George Noory. KKOH (Reno, Nevada; 50 kW) vs. KAZM (Sedona, AZ; 5 kW daytime, 0.25 kW nighttime). With Reno about 200 miles away and the more desirable Sedona over 700 miles away, the 50 kW station dominates the frequency every which way.
I wish I could take two identical radios, tune them to the same frequency, set one in DX mode and the other in local mode, then subtract one signal from the other. That should produce just the distant signal. That kind of setup would probably require software. It would only be a rare situation where I would want to manage a computer and two radios at the same time.