The signal is quickly identified as an "echo" of a landmark 1901 wireless test by Marconi, and is shortly followed by similar snippets of other early transmissions.
All are extremely powerful, blanket the entire frequency spectrum, and repeat themselves in loops ranging from one-half to thirty seconds in length.
However, after a few days, the signals become non-directional; a prominent scientist is interviewed and explains that this can only mean that the mysterious radio sources have arrived on Earth.
Society begins to adjust to its absence, but after only a few additional weeks people notice that thunderstorms are no longer accompanied by lightning; shortly thereafter, all electrical devices start faltering.
The story skips forward a few years: there have been no major societal disruptions, but the US has reverted to a late-Victorian technological level, with the return of steamships, horses, and buggies.