The development of the Radio Merit Badge over the years is quite fascinating. The original merit badge was titled the Wireless Merit Badge and was introduced in 1918. I've been able to capture some of the covers from the National Scouting Museum archives.
I've also posted some of the requirements taken from the same pamphlets. Note that the 1922 requirements included being able to receive Morse Code at 10 words per minute. The 1930 Radio Merit Badge lowered the requirement to 5 wpm. The code requirement was dropped completely in 1984 and three options were added to the requirements: amateur radio, broadcast radio, and shortwave listening.
The impact of these changes, along with the revised pamphlet, appear to have caused a renewed interest in the merit badge. In 1984 the number of Radio Merit Badges was less than 1,000. By 2010 that number had seen steady growth over the years to hit 7,000! The total earned in its history as of 2010 is 145,395.