1. How Does a Radio Make Sound Without Batteries or Plugs?
In AM broadcasting, the strength of the radio wave is changed to match the shape of the sound. On the receiving side, the listener first uses "tuning" to select the radio wave of the desired station. Next, "detection" (or demodulation) extracts the sound signal. During detection, a component that allows current to flow in only one direction is used to keep only the upper (or lower) half of the wave. The earphone then smooths out the fine components to create sound [6]. The medium-wave band used for AM broadcasting in Japan is about 525 to 1605 kHz [6].
A crystal radio performs this detection using the contact between a mineral and metal. It is a type of unpowered radio that connects to an antenna and ground, and is listened to with a receiver (earphone) [5]. While the Akita College of Technology materials explain this using modern components, the mechanism of rectification—allowing current to flow in only one direction—is the same [6].
Why are batteries not needed? When electrons in the metal of the antenna are pushed by radio waves, they shake, creating an alternating current. Rectifying this current extracts the sound components [7]. Because the energy of the radio wave itself is used instead of a battery, the sound becomes weak, resulting in a format where one person listens alone [5]. It is somewhat similar to a string telephone, but radio waves carry the vibration instead of the string, and a rectifying component is inserted in the middle.
2. How the Great Kanto Earthquake Made People Want Radio in Japan
During the Great Kanto Earthquake of 1923, newspaper companies were also damaged, causing delays in publication and distribution. Amid the lack of information, rumors spread, and voices saying "if only we had radio" grew louder. It is said that this demand helped push for the opening of radio stations [4]. Japan’s first radio station was established about a year and a half after the earthquake [4].
However, the earthquake was not the only cause. The same source states that the government had been considering implementing broadcasting since around 1922, and newspaper companies were also moving to promote its adoption [4]. It seems accurate to read the launch as a combination of "the anxiety of that day" and "the flow of preparations that were already underway."
3. When Did Radio Broadcasting Start in Tokyo in 1925, and When Did Regular Broadcasts Begin?
Broadcasting in Tokyo started in several stages. There was an experimental broadcast on March 1, 1925, a provisional broadcast on March 22, and the regular broadcast from Tokyo began on July 12. The regular broadcast was conducted with an output of 1 kilowatt from a new station building erected at Atagoyama in Shiba [1].
At 9:30 AM on March 22, the Tokyo Broadcasting Station (the predecessor of today’s NHK) began provisional broadcasting on medium waves. This day is now celebrated as "Broadcasting Memorial Day." The first day’s broadcast reportedly included news, weather forecasts, and market prices for stocks and commodities [2].
It did not start all at once nationwide. Osaka began provisional broadcasting on June 1, and Nagoya’s regular broadcast started on July 15 [1]. Remembering that "Japanese radio started all at once on July 12" is slightly inaccurate.
4. Why Were Most Daytime Radio Broadcasts Stock Prices?
In the early days, weekdays during the daytime were largely occupied by stock market prices and commodity quotes. From 9 AM to 4 PM, when the market was open, excluding the lunch break, most of the time was dedicated to these financial updates [1]. This is quite different from the current feeling. On Sundays and holidays, entertainment programs were the main focus [1].
On the first day of regular broadcasting, July 12, 1925, the broadcast is introduced as having started with a weather forecast. It was followed by news, home-oriented lectures, music, language courses like junior high English and practical English, talks on cooking and household finances, and stories for children. The broadcast lasted about 8 hours, from 9 AM to 5 PM [3].
5. How Radio Listener Contracts Grew from 5,455 to 1 Million
The listening fee was 2 yen per month, but it was reduced to 1 yen during the provisional broadcast period [1]. At the start of broadcasting, there were 5,455 listener contracts. This increased to about 390,000 in 1926, which is an increase of about 71 times. In the early 1930s, it surpassed 1 million [9].
In the early days, crystal radios were mainstream, and earphone listening was common [1]. With improvements in vacuum tubes, radios became able to take power from household lighting circuits. Crystal radios did not require a power source but could only be listened to with a receiver [8]. Technological advances around 1928 to 1931 are said to have helped push this spread [8].
6. How Radio Brought Live Baseball Commentary and Radio Calisthenics Using Only Sound
On August 13, 1927, the 13th National Middle School Championship Baseball Tournament (the current national high school baseball tournament) was broadcast on radio. It is considered Japan’s first live sports commentary broadcast [12]. This date comes from an encyclopedia entry, and the broadcasting station and venue are points that might be worth verifying in original materials.
Radio calisthenics was born in 1928. It was announced under the name "National Health Calisthenics" on October 29, 1928, and broadcasting began at the Tokyo Central Broadcasting Station on November 1. The history includes a proposal by a Ministry of Communications official who learned in the United States of an insurance company’s plan to broadcast exercises, suggesting it as a project to celebrate the enthronement of Emperor Showa [10]. The current "Radio Calisthenics No. 1" was decided on in 1951 as the third version [10].
NHK’s television regular broadcasting began on February 1, 1953 [11]. From the start of radio (March 1925) to the start of TV (February 1953), it was about 28 years (specifically 27 years and 11 months).
7. How to Compare Today's Program Schedule with the Radio Schedule of July 12, 1925
Using a newspaper or web program guide, compare the programs from morning to evening with the schedule for July 12, 1925. That day lasted about 8 hours from 9 AM to 5 PM and started with a weather forecast [3]. What has increased in today’s program guides, and what has disappeared? If you have a radio, tuning to AM (medium wave) and listening is one way to experience this.
If you want to read more, the explanations from the Japan Radio Museum [1] and the paper on the earthquake and media [4] are suitable for grasping the framework of this story.