[Antennas] Think I've got this figured out, Re: AM Broadcast RX Antenna?

[Richard (Rick) Karlquist]

All modern car radios use a 30 inch whip, because that is
a quarter wave on 98 MHz, the center of the FM band.
Meanwhile, on AM, the radio is designed to resonate out
the total capacitance of the whip and the cable.  Older
radios had an adjustment so you can change the length of
the whip and peak for maximum sensitivity.  I doubt
that you will still find this adjustment.

If you want to convert to a CB whip, you need to put
enough inductance in series with it to cancel out the
additional capacitance the CB whip has.  You don't want
to tune the whip to resonance, just reduce its effective
capacitance.  This can only be done for one specific
frequency of course, but that is all you need.

Rick N6RK