I remember a TV program, in Spain in the 70's. They explained how to do one AM radio with one transistor, an AA battery, half a metre of copper wire and an earp

I remember a TV program, in Spain in the 70's. They explained how to do one AM radio with one transistor, an AA battery, half a metre of copper wire and an earphone. Worked fine. 20 m? It used the mattress base as antenna.