Did you spend some time thinking about the available bandwidth of various amateur bands?

As an amateur licence holder, you can access six different amateur radio frequency bands: 80m, 40m, 15m, 10m, 2M and 70cm. If the bandwidth of each of these bands is added together, a total of 26.65mhz bandwidth will be obtained, which can be used in Australia.

I can tell you that this is a large bandwidth, but before I give you the above background, you may not imagine that the bandwidth is as wide as 26.65mhz.

Radio is all electromagnetic waves. Like all waves, electromagnetic waves have their own frequencies, that is, the number of electromagnetic field oscillations per second. A simple electromagnetic wave that oscillates like a beautiful sine wave has only one frequency – such a pure single frequency electromagnetic wave can be understood as a radio with zero bandwidth, which does not contain any information.

However, such a zero bandwidth signal is the basis of radio transmission of information. We usually use it as a “carrier” to load the signals that need to be transmitted, such as sound, image and data. There are many ways to load, we call it “modulation method”. The simplest is am (such as AM Broadcasting), which is to change the oscillation intensity of the radio according to the signal to be transmitted. A little more complicated is FM (such as FM radio and Bluetooth), which changes the frequency of the radio according to the signal to be transmitted. There are many other complicated modulation methods, so I don’t need to talk about them.

No matter what modulation method is used, the result will lead to the frequency of the original carrier is no longer fixed in the original position, but swing back and forth near the original frequency. We have a kind of instrument called “spectrum analyzer” which can directly observe the oscillation. Generally speaking, its swing amplitude is almost its “bandwidth”“ The more bandwidth a radio has, the more information it can load.

In addition, there are a lot of government regulations and industry standards to limit the carrier frequency and bandwidth. For example, transmitting radio waves with a bandwidth of 2MHz in the 1MHz frequency band of AM broadcasting is prohibited by law.

Ultimately, what kind of radio bandwidth is not determined by the radio itself, but by national laws and industry standards. For example, the bandwidth of Wi Fi and ultra wideband signals is very large, while the bandwidth of radio broadcasting is very small.


Post time: Apr-27-2021