Loopstick (ferrite rod) antenna circuit model
A ferrite rod antenna generates a voltage in series with the coil. After all, the signal is coming from free-space and gets concentrated magnetically by the ferrite to produce maybe 2 or 3 times more induced voltage in the coil. However, that induced voltage is in series with the rod's coil-inductance and can, therefore form a very effective voltage amplifier when used in conjunction with a tuning capacitor: -

The above image shows the tuning effect at 503 kHz when L = 100 uH and C = 1 nF. They are values I chose to be about right at 500 kHz - notice how much voltage amplification it produces (maybe 30 dB) on top of that due to flux concentration by the ferrite rod.