But it was difficult to call them even radio receivers Because in fact they were only recorders of electromagnetic oscillations with zero selectivity … in a very wide range of frequencies, including discharges of electromagnetic waves from the nearest thunderstorm there are no input resonant circuits, no SOUND signal demodulator detector… not even a loudspeaker or headphones. There is only the most primitive mechanical coherer detector and attention … a bell. ))) all they were capable of was receiving a single signal, like Popov's radio … or a continuous signal like Marconi radio from primitive spark radio stations in telegraph mode … and signal their arrival with a bell instead of a loudspeaker it was not for nothing that spark radio stations and receivers of those times were called wireless telegraph.