What you are saying seems very confusing, and I don't follow it. I do think you are making a simple definition overly complicated. I don't feel that definition is particularly good either, but I wouldn't worry too much about it.
Basically, they are saying that a radio channel is one channel in a band of many channels. The air, is a multiplexed medium (frequency multiplexed), which many channels, including AM channels, FM channels, TV channels etc.
In the case of a wire (or optical fiber) you might have one channel dedicated to that medium.
Also, you are incorrect that a radio channel can't be multiplexed, because you can multiplex channels within a channel. If the channel is digital, then time division multiplexing can be used. Here in the USA, digital TV channels have secondary audio channels (for other languages) built into the data (SAP). There is also captions available, and additional information is encoded as well. One can even put 2 or more complete video channels into the data with higher compression ratios.
Even the old analog TV channels encoded additional information. The color information was added later, but black and white TV could still be watched. Also, the audio is at a frequency offset from the video information, so this is really two channels put into one channel.
The bottom line is that reality is alway more complicated that our classifications and terminology would indicate. Thats why I say, don't worry to much about definitions. Definitions and terminology give you a black and white view of the facts. Reality is shades of grey and colors, which should appeal to a painter guy.
Basically, they are saying that a radio channel is one channel in a band of many channels. The air, is a multiplexed medium (frequency multiplexed), which many channels, including AM channels, FM channels, TV channels etc.
In the case of a wire (or optical fiber) you might have one channel dedicated to that medium.
Also, you are incorrect that a radio channel can't be multiplexed, because you can multiplex channels within a channel. If the channel is digital, then time division multiplexing can be used. Here in the USA, digital TV channels have secondary audio channels (for other languages) built into the data (SAP). There is also captions available, and additional information is encoded as well. One can even put 2 or more complete video channels into the data with higher compression ratios.
Even the old analog TV channels encoded additional information. The color information was added later, but black and white TV could still be watched. Also, the audio is at a frequency offset from the video information, so this is really two channels put into one channel.
The bottom line is that reality is alway more complicated that our classifications and terminology would indicate. Thats why I say, don't worry to much about definitions. Definitions and terminology give you a black and white view of the facts. Reality is shades of grey and colors, which should appeal to a painter guy.