Hi…It’s hard enough finding the right tuning capacitor for the AM BC band. The AM band goes from 550 to 1710 kHz, a ratio of just over 3:1. The capacitor needs to have a range of 9:1 as the capacitance varies as the square of the frequency, so the common value of 50 to 450pF just doesn’t quite cut it. It gets worse as you go down to the longer wavelengths and adding fixed capacitance reduces the tuning range even more.
