For me a radio is a box with the knob to rotate.
Now at FM no brakes between stations. At AM are.

What was in 1915?
S*


In 1915 there were no broadcast stations to speak of so your dial
would be just one large "brake" (sic).

"Well, it's like this. The story starts in 1915, when mankind discovered
sidebands. Now possessing this superior understanding of the AM signal,
radio scientists began to understand the implications of their discovery.
Soon afterwards, our old friends at Bell Labs, who have discovered
practically everything, developed a method for removing one of the
sidebands
of an AM signal but retaining all the essential modulation components.
As an
expert of that day supposedly said, "both sidebands are saying the same
thing" (Goodman, 1948). " From:
http://www.hamradiomarket.com/articles/SSBHistory.htm

If in 1915 were no broadcast stations to speak tell us what was with the
first station to speak and when it start transmitting.
S*


The first AM Broadcast station (as opposed to amateur or military ) was
in about 1919.

Jeff