Di-Rectional.....

[Don A]

Maybe Dan or some other technical mind can answer this.

I know the first (licensed) stations on the air around 1921-ish....

When did the engineers discover directional antenna patterns?

What year did the first directional array go into effect?

The technology (if you can call it that) has been around for a long 
time....but seems rather "hi-tech" for the 20's and 30's.....