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Secrets of how TV works! - the most important part of a broadcasting tower

  • MitaSo it's because of the digital terrestrial TV transmitter that many viewers are able to watch the programs we produce in their homes!
  • HidakaExactly. If there was no digital terrestrial TV transmitter on the Tokyo Skytree®, then it would not fulfil its role as a broadcasting tower.

Photo: Transmitter for digital terrestrial TV broadcastsTransmitter for digital terrestrial TV broadcasts

  • MitaThis means that a digital terrestrial TV transmitter is the most important part in the function of a broadcasting tower. Even so, the Tokyo Skytree sends radio waves throughout Japan, doesn't it? Hmmm. That's an amazing amount of power, isn't it!
  • HidakaNo, not quite.
  • MitaOh. Am I wrong? It's the highest in the world, right?
  • HidakaIt is the highest self standing broadcasting tower in the world, though this does not mean that radio waves are being sent throughout Japan by just the Tokyo Sky Tree® alone.
  • MitaReally!?
  • HidakaOnly the Kanto region of Japan receives radio waves from the Tokyo Skytree. There are also some places that cannot receive radio waves, so "relay stations" are located in between so that radio waves can be sent from there to areas where radio waves cannot reach. By the way, in other prefectures, each TV station sets up a large transmitter called "master stations" and radio waves are output independently from each of these.
  • MitaCome to think of it, when I go on a reporting trip to other prefectures, I'm sometimes surprised that programs broadcast during the daytime in Tokyo are aired in the evening. This is because transmitters differ according to the prefecture, right? I understand this now!
  • HidakaYes, that's right. By the way, NEC holds an approximate 50% share of large digital terrestrial TV transmitters called "master stations" in Japan. Because the manufacture of large digital terrestrial TV transmitters involves handling high-power electricity and requires high-level reliability, only a limited number of companies throughout the world manufacture large digital terrestrial TV transmitters.
  • MitaReally? So considerable technology is packed into these, aren't they. Which reminds me that the director of the programming division often mentions that "broadcasting services must not stop even for 1 second." It would certainly be awful in the unlikely event that a digital terrestrial TV transmitter malfunctioned. Have broadcasts ever stopped before?
  • HidakaYes, they have. But only rarely. If a transmitter breaks down, broadcasting would surely stop, too.
  • MitaWhat would happen if a broadcast stopped?
  • HidakaWith digital broadcasts, the screen would become completely blue and freeze. At around the time of analog broadcasts, the screen would start to look like a sandstorm, or lines would suddenly appear on screen or the screen would momentarily turn black, or other similar phenomenon would appear. These were due to transmitter trouble, but they would often clear up in a short time. However, with digital broadcasts, signal processing is complex, so if the source is suddenly and completely cut off, broadcast service stops for a whole 20 or 30 seconds. This is conspicuous so viewers will be very inconvenienced if digital broadcasts stop.
  • MitaWow, that's a lot of pressure, isn't it! Are there any means or measures to prevent broadcast service from being stopped?
  • HidakaYes, there are. One technique to prevent this is the switching function. In many cases, two or more digital terrestrial TV transmitters are installed and operated for digital broadcast service. This is mainly to prevent a stop in broadcasting by automatically switching to the one which is operational in the unlikely event that one of the transmitters malfunctions.
  • MitaI see. So, you mean that even if one transmitter breaks down, you are safe since you still have one more transmitter as a spare.
  • HidakaYes, exactly. Note, however, that since digital terrestrial TV transmitters handle extremely complex signals and large amounts of electrical power, it is still technically very difficult to switch over smoothly to the other transmitter.
  • MitaSo, maybe sparks might fly out because of switching...?
  • HidakaIt's possible, you know.
  • MitaReally!?
  • HidakaIf a person without specialist knowledge makes a transmitter, this kind of thing is possible even with the same design drawings. Since these equipment handle large amounts of electrical power, advanced skills are required for assembly.

Tokyo Skytree® is a registered trademark of Tobu Railway Co., Ltd. and Tobu Tower Skytree Co., Ltd.

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