Ferrite antennas are remarkably efficient considering their size. If one were to examine the magnetic flux around a ferrite antenna one would find that the flux

Ferrite antennas are remarkably efficient considering their size. If one were to examine the magnetic flux around a ferrite antenna one would find that the flux is channeled from the surrounding area into the ferrite rod (the rod effectively concentrating the field). In effect this makes the antenna's effective size (its aperture) much bigger than its actual physical size. Also, remember broadcast services are designed to put sufficient field (signal) strength into a 'notional' receiver that's operating within the rated service area of the broadcast. Both the transmitter field strength and the receiver sensitivity are designed in combination to provide a worthwhile listening signal. The designed signal-to-noise ratio is dependent on the type of service and for the AM B/C band it is in the order of 40dB or so for the primary service area (the secondary service area typically 10dB less).