Communication mode selection of selected wireless module

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Communication mode selection of selected wireless module [Copy link]

First, let's take a look at how far wireless devices can communicate:

Before 1949, there were no communication satellites in the sky, and the Shanghai underground party could report to Yan'an with a radio station with a power of a few watts. Of course, this used shortwave reflected by the ionosphere. Even now, a large number of amateur radio enthusiasts can still use 5W of power to communicate thousands of kilometers. Even if it is using the commonly used 430MHz frequency band ultra-short wave communication, a large number of amateur radio enthusiasts can also use a few watts of power at 430M to use amateur communication satellites with a perigee of more than 1,000 kilometers for intercontinental communication and text and image transmission.

How far can the actual wireless devices communicate? For example, the 430Mhz frequency band we often use is also called the line-of-sight frequency band. For example, it can communicate with anything that can be seen with the naked eye. Some people say, "I saw the moon." Yes, it can communicate with anything. Not only that, a large number of radio enthusiasts around the world use the 430M frequency band to communicate by reflecting the moon's surface, which can cover half of the earth. A better example is that there are amateur radio stations on the International Space Station, and the power of everyone's communication is not large.

More realistically, right now, how far can 1 milliwatt of power communicate? This is easy to try. Find an RF signal source and connect it to an antenna to send FM signals with a frequency deviation of 75khz and 5khz respectively. Use a better amateur radio walkie-talkie to receive in wideband mode and narrowband mode in an open area. It is found that the wideband signal fails within 100 meters, while the narrowband signal can reach many times farther. So the bandwidth determines the distance, because the energy density is not concentrated. Try 20mw again and find that the narrowband FM communication can easily reach 20km when the antenna is good, while the wideband signal is very close. This explains why radio and television stations have such high-power transmission towers. So when there is a communication distance requirement, you should first choose which communication mode to use.

1. How much power should be used:

Find a spectrum analyzer and connect it to an antenna. Then find a walkie-talkie 5 meters away from the instrument, press the transmit button, and you can see the transmitted spectrum. Shake the walkie-talkie in a large range with your hand, and you can find that the spectrum changes a lot, with a change of more than 10db, so if you want to use it on the move, you must have about 10 times the power margin to use it well.

2. How to expand the communication distance:

Networking. Whether it is a large-area network or a complex small-area network, the reliability of long-distance communication can be greatly improved. Any measures such as increasing the transmission power will not make a qualitative change. Because this series of chips is not used for long distances.

Long-distance communication mainly focuses on the receiver. In the 430M frequency band, for example, there must be at least two intermediate frequencies and good filters. For narrowband, there are a large number of ready-made crystal and ceramic filters to choose from, but the selection of broadband filters is not so easy. It can be said that it is very complicated and costly to make them at high specifications. The filter basically determines the quality of your receiver.