I have a Radio Shack AM antenna (loop about 1 ft in diameter encased in plastic. Like the Terk above it must be fine tuned to the station selected by the rotation of a dial. It can be hard wired to an am antenna input or just set next to the am tuner. WAG, they don't make them any more. :-(
But if that is the case Google up Crane - they sell a lot of radios and, last time I was there they had a very similar product.
BTW, it works! I'm using mine next to my Tivoli radio.