Around 1970, I acquired a little transistor radio (powered by 4xAA cells, 6V) that had no external antenna. Inside the back panel (which opened to allow replacing the battery cells) one could see the loopstick antenna, just a ferrite rod with a lot of turns of fine wire that connected to the circuit board. I used to get KGO AM (IIRC around 800 kHz), from San Francisco, in central Washington state at night with this little receiver.
I've always wondered how a loopstick like this can act as an antenna. The wire is wrapped tight (the coil length I recall from this radio was around half an inch, close wound; others I've seen that were coming apart seemed to be wound in layers, suggesting hundreds of turns) on a paper sleeve around the ferrite. The antenna is only slightly directional; the weakest of stations would fade when the radio was rotated 90 degrees from where they were strongest.
What I picture in my head is that the ferrite permeates with the magnetic component of the signal to be received, and its fluctuating field induces a voltage in the wire coil which is then amplified before going into the IF stage.
Am I understanding this correctly?