Today is Broadcasting Day (放送記念日), marking the day on which, in 1943, NHK as we know it was established. And that day was chosen because it was the 18th anniversary of Japan's first radio broadcast:

「アーアーアー、聞こえますか。JOAK、JOAK、 こちらは東京放送局であります。」
"Ahh, ahh, ahh, can you hear me? JOAK, JOAK, this is the Tokyo Broadcasting Office."

The "Ahh, ahh, ahh" was apparently designed to give listeners a chance to fine-tune their crystal sets.

I should note that NHK themselves claim to have been around since well before 1943. I assume the discrepancy is caused by some technical/legal issue that I don't care about.