You're correct Dick, it is impedance. And when "Broke" said "All an IC corcuit can do is guess and assume" my guess is that he meant to say an LC circuit which would be tuned to maximize for the RX frequency and to compensate for antenna error. This is "one" of the reasons we send our RX's in for tuning/testing.

http://en.wikipedia.org/wiki/Coaxial_Cable