How to distinguish whether the signal is high frequency or low frequency

The circuit board manufacturer, circuit board designer and PCBA manufacturer explain how to distinguish whether the signal is high frequency or low frequency

High frequency corresponds to low frequency. High frequency refers to radio waves between 3MHz and 30MHz. Low frequency mainly refers to the lowest frequency range applied in a certain technICal field. In specific applications, because of their different transmission characteristics, they will also have different uses.

In terms of its nature, it mainly has the following differences:

1. High frequency signal has many carrier frequency points and high information transmission rate.

2. The size of the transmitting antenna is related to the wavelength of the signal. High frequency signals can be transmitted with a SMAller antenna. For example, the length of a mobile phone is generally more than ten centimeters, which is actually related to the length of the antenna. Then it corresponds to the 900M frequency band, which can be known after calculation.

3. High frequency signal is easier to achieve high-power transmission than low frequency signal, so although the signal attenuation is fast, high frequency signal is still used for LOS transmission. Low frequency signal is generally used for network coverage because of its wave growth, small fading during transmission, and easy scattering and diffraction during transmission.

From the above analysis, if the signals on 400MHz and 3G frequencies are in the wireless network (I mean in the absence of special standards and definitions), we generally use 400M for coverage and wireless access at the mobile end. 3G is used for base station communication. Because the frequency is high and easy to attenuate, the line of sight transmission is selected, that is, the base station is set high to avoid building occlusion, and the transmission data rate is high.

When high frequency is used for system design, the requirements for wiring are higher, and the performance of the whole system will be greatly affected by a slight interference. High frequency attenuation is large, transmission distance is short, and high frequency is not easy to amplify the signal, and the attenuation is relatively large. Therefore, using low frequency band in the uplink of communication can reduce the transmission power of mobile phones.

In the FDD communication system, generally, the uplink uses low frequency and the downlink uses high frequency. Because of the large attenuation of high frequency and power consumption, it is generally provided by the base station. At present, in 2G mobile communication, the optimal communication frequency is mainly concentrated in 900M. This frequency point has a long transmission distance and good coverage effect. It is mainly used for macro cell coverage with large capacity, while the 1800M frequency point has a relatively high frequency and poor transmission distance, However, the penetration effect is better, which is mainly used for microcellular or cell cracking. However, 3G uses frequencies above 2.1G, but the modulation and coding methods used are completely different, and the power control is more accurate. It can't be said that high frequencies are bad, but it depends on how to use them.

In another way, from another angle, we generally refer to the notes Do, Re and Mi when we talk about high pitch and low pitch. Some people can sing very high and some people can sing low, but these have nothing to do with "high frequency and low frequency".

If we sing the same song with the same backing tape, we can hear that some people sing with sharp voices and some sing with low voices. Take Fei Yuqing and Jay Chou's chorus of "A Thousand Miles Away" as an example. It should be obvious that Fei Yuqing's voice is relatively clear, while Jay Chou's voice is relatively thick.

This feeling can represent that Fei Yuqing's voice is more "high-frequency", while Jay's voice is more "low-frequency". (The voice of riddle: Actually, Jay Chou's voice should be in the middle frequency rather than the low frequency)

For another example, if there are knobs MARKed "Treble" and "Bass" on your home stereo, you can play a song, and then try to turn the treble button to the maximum to see if you can hear the whole music sharpen a lot; Turn the treble button to the minimum, and the music should become as if it is stuffy in a pot.

This is the effect of increasing and decreasing high frequency.

In the same way, try low frequency (the bass button on the stereo). If you add it to the maximum, the music will become thick or a little fuzzy. If you reduce the low frequency, the music will become very thin and weak. PCB manufacturers, PCB designers and PCBA manufacturers will explain how to distinguish whether the signal is high frequency or low frequency.