{"id":9468,"date":"2022-11-15T14:36:21","date_gmt":"2022-11-15T06:36:21","guid":{"rendered":"https:\/\/store.west-hn.com\/?p=9468"},"modified":"2022-11-25T11:03:16","modified_gmt":"2022-11-25T03:03:16","slug":"iot-communication-technology-rf","status":"publish","type":"post","link":"https:\/\/store.west-hn.com\/en\/iot-communication-technology-rf\/","title":{"rendered":"[Internet of Things Communication Technology]--Radio Frequency Technology"},"content":{"rendered":"

summarize<\/h1>

Radio frequency (RF) is the rate of oscillation of an alternating current, voltage, magnetic, electric, electromagnetic field electrical or mechanical system at frequencies ranging from about 20 kHz to about 300 GHz. Through the use of antennas and transmitters, RF can be used for various types of wireless broadcasting and communications. InIoT wireless communication<\/a>This article briefly describes some of the concepts of RF technology, which is widely used in various RF technologies.<\/p>

ISM radio frequency band<\/h1>

The ISM radio bands are internationally recognized for industrial ((Industrial)<\/strong>Science (Scientific)<\/strong>and medical care (see annex I).M<\/strong>The ISM bands are a portion of the radio spectrum reserved for ISM purposes and do not include telecommunications applications. Typically, communications equipment operating in the ISM bands must be able to withstand any interference generated by ISM applications, and users are not protected by regulation for the operation of ISM equipment in these bands. The fastest growing use in recent years has been in short-range, low-power wireless communication systems, as these bands are often approved for such devices and can be used without government licenses that would otherwise be necessary for transmitters; ISM frequencies are often chosen for this purpose because they already must tolerate interference problems. Cordless phones, Bluetooth devices, near-field communication (NFC) devices, garage door openers, baby monitors, and wireless computer networks (Wi-Fi) may all use ISM frequencies, although these low-power transmitters are not considered ISM devices.<\/p>

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Global ISM band<\/figcaption><\/figure>
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Globally recognized: 2.4GHz - 2.5GHz frequencies as license-free ISM bands<\/figcaption><\/figure>

RF Name Explanation<\/h1>

Relationship between frequency and wavelength<\/h2>

The unit of measurement of radio frequency is hertz (Hz), which indicates the number of cycles per second when a radio wave has been transmitted. One hertz equals one cycle per second.
Example.
a. Frequency - number of cycles per second (Hz) - e.g. 2MHz
b. Period - the duration of the completion of a cycle.
c. Wavelength - the distance at which the waveform repeats itself<\/p>

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RF measurement unit dB<\/h2>

dB: decibel, the logarithmic (equal to 10 times) ratio of the difference between two values. Master sites use dB to measure the ratio of transmitted signal energy to reflected signal energy. A common rule of thumb is to double the power and increase it by 3 dB, and halve the power and decrease it by 3 dB.<\/p>

If 0 dBm represents 1 mW; 10dB = 0.01W ; 20dBm = 0.1W ; 30dBm = 1W<\/p>

\"\"<\/figure><\/div>\n\n

If the power of the carrier (reference signal) is C = 0.1 mW and the power of the noise signal is S = 10 \u03bcW.<\/p>\n\n

The reference signal power expressed in decibels is:<\/p>\n\n

\"\"<\/figure>\n\n

The noise power expressed in decibels is:\"{\\displaystyle<\/p><\/div><\/div>

dBc (decibels relative to the carrier) is the power ratio of the signal to the carrier signal, expressed in decibels.If this transmitter outputs a maximum of 600W\/57.78dBm, the harmonics will be no greater than 60mW\/17.78dBm!<\/strong><\/p>

Why 50 ohms is the most common standard impedance for cable and antenna work<\/h2>

Why is it that in many RF systems or components a 50 ohm impedance is often used (sometimes this value is even the default value of the PCB) , why not 60 or 70 ohms? How is this value determined and what is the meaning behind it?<\/p>

There are two characteristics that affect the transmission of RF signals, transmission power and loss. We expect that wireless signals can be transmitted farther in the case of low loss, in 1929, Bell Labs did a lot of experiments, and ultimately found that in line with this high-power transmission, loss of coaxial cable with its characteristic impedance are 30 ohms and 77 ohms. Among them, 30 ohm coaxial cable can transmit the maximum power, 77 ohm coaxial cable transmission signal loss is the smallest. 30 ohm and 77 ohm arithmetic mean value is 53.5 ohm, 30 ohm and 77 ohm geometric mean value is 48 ohm.<\/p>

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Power versus impedance<\/figcaption><\/figure><\/div>\n\n
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Loss\/Length vs. Characteristic Impedance<\/figcaption><\/figure><\/div><\/div>

Impedance (Impedance<\/strong>)<\/h2>

In a DC circuit, the resistance to current is simply called resistance. In an AC circuit, the resistance is called impedance. That is, impedance (measured in ohms) is the effective resistance to the flow of current around a circuit that contains both AC resistance and AC reactance. Impedance has two parts, \"real\" and \"imaginary\".<\/p>

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