The RF signal output by the radio transmitter is transmitted to the antenna through a feeder (cable) and radiated by the antenna in the form of electromagnetic waves. After the electromagnetic wave reaches the receiving location, it is received by the antenna (only a small fraction of the power is received) and sent to the radio receiver via the feeder. Therefore, in the wireless network project, it is very important to calculate the transmitting power of the transmitting device and the radiation capability of the antenna.
Tx is an abbreviation for Transmits. The emission power of radio waves refers to the energy within a given frequency range. There are usually two standards for measurement or measurement:
Power (W) - linear level relative to Watts.
Gain (dBm) - relative to 1 milliwatt (Milliwatt).
The two expressions can be converted to each other:
dBm=10xlog[power mW]
mW=10[gain dBm/10dBm]
In a wireless system, an antenna is used to convert a current wave into an electromagnetic wave. During the conversion process, the transmitted and received signals can also be "amplified," and this measure of energy amplification becomes "Gain." The antenna gain is measured in "dBi". Since the electromagnetic wave energy in the wireless system is generated by the transmitting device's transmitted energy and the antenna's amplification and superposition, it is best to measure the transmitted energy with the same metric-gain (dB), for example, the power of the transmitting device is 100mW, or 20dBm; the antenna The gain is 10dBi,
Then: total transmit power = transmit power (dBm) + antenna gain (dBi) = 20dBm + 10dBi = 30dBm or: = 1000mW = 1W
Each dB is very important in a "low-power" system, with particular attention to the "3dB rule." Each increase or decrease of 3dB means that the power is doubled or reduced by half: -3dB = 1/2 power - 6dB = 1/4 power + 3dB = 2x power + 6dB = 4x power For example, 100mW of wireless transmission power is 20dBm The 50mW wireless transmission power is 17dBm, while the 200mW transmission power is 23dBm. 0dbm=0.001w left plus 10= right multiply 10
So 0+10DBM=0.001*10W, ie 10DBM=0.01W, so 20DBM=0.1W30DBM=1W40DBM=10W
Also add 3=right multiply 2 to the left, such as 40+3DBM=10*2W, ie 43DBM=20W
For example, if the machine 20W uses 30 meters 50-7 (physical foam low-loss cable) at 400 MHz frequency, how much gain is left on the antenna 20W=43DB30 meters 50-7 loss one meter less than 0.09 according to the maximum value 0.09*30=2.7DB
43DB-2.7DB=40.3DB Antenna gain 16DBi+40.3DB=56.3DB
For the above example, we can see that the gain and power do not change linearly, so we can't just look at the emission state from the power point of view. When your machine is gaining 43DB at 20W, and 49DB at 46DB60W at 40W, conversely, when the power is lost in half, you have just lost 3 DBs, which is not particularly significant for signal propagation. But if you look at the power, you're already half less. You think that the ability to transmit is also a half smaller. Therefore, looking at power here is quite wrong. The loss of 3 dB of the feeder to the antenna part has been improved. When your antenna is 16 DBi, the power of the low-power station far exceeds the use of high-power radio small antenna. This is also a lot of friends use the hand-feeder bar antenna The effect is also good.
If you really care less about power than a test, the output of the transmitter is not connected to the coaxial cable, but to the 380V power cable. The same number of meters, the power cable loss must be very small, because the power = current * voltage, power The small internal resistance of the cable will share little voltage on the cable, and the small power loss will be small. However, the high-frequency signal is the skin effect propagation. The power cable cannot transmit high-frequency signal loss. It will be quite large. It can be said that a little common sense friends know that Power cables cannot be used as feeders. From this point it is also proved that looking at power alone is totally wrong.
Tx is an abbreviation for Transmits. The emission power of radio waves refers to the energy within a given frequency range. There are usually two standards for measurement or measurement:
Power (W) - linear level relative to Watts.
Gain (dBm) - relative to 1 milliwatt (Milliwatt).
The two expressions can be converted to each other:
dBm=10xlog[power mW]
mW=10[gain dBm/10dBm]
In a wireless system, an antenna is used to convert a current wave into an electromagnetic wave. During the conversion process, the transmitted and received signals can also be "amplified," and this measure of energy amplification becomes "Gain." The antenna gain is measured in "dBi". Since the electromagnetic wave energy in the wireless system is generated by the transmitting device's transmitted energy and the antenna's amplification and superposition, it is best to measure the transmitted energy with the same metric-gain (dB), for example, the power of the transmitting device is 100mW, or 20dBm; the antenna The gain is 10dBi,
Then: total transmit power = transmit power (dBm) + antenna gain (dBi) = 20dBm + 10dBi = 30dBm or: = 1000mW = 1W
Each dB is very important in a "low-power" system, with particular attention to the "3dB rule." Each increase or decrease of 3dB means that the power is doubled or reduced by half: -3dB = 1/2 power - 6dB = 1/4 power + 3dB = 2x power + 6dB = 4x power For example, 100mW of wireless transmission power is 20dBm The 50mW wireless transmission power is 17dBm, while the 200mW transmission power is 23dBm. 0dbm=0.001w left plus 10= right multiply 10
So 0+10DBM=0.001*10W, ie 10DBM=0.01W, so 20DBM=0.1W30DBM=1W40DBM=10W
Also add 3=right multiply 2 to the left, such as 40+3DBM=10*2W, ie 43DBM=20W
For example, if the machine 20W uses 30 meters 50-7 (physical foam low-loss cable) at 400 MHz frequency, how much gain is left on the antenna 20W=43DB30 meters 50-7 loss one meter less than 0.09 according to the maximum value 0.09*30=2.7DB
43DB-2.7DB=40.3DB Antenna gain 16DBi+40.3DB=56.3DB
For the above example, we can see that the gain and power do not change linearly, so we can't just look at the emission state from the power point of view. When your machine is gaining 43DB at 20W, and 49DB at 46DB60W at 40W, conversely, when the power is lost in half, you have just lost 3 DBs, which is not particularly significant for signal propagation. But if you look at the power, you're already half less. You think that the ability to transmit is also a half smaller. Therefore, looking at power here is quite wrong. The loss of 3 dB of the feeder to the antenna part has been improved. When your antenna is 16 DBi, the power of the low-power station far exceeds the use of high-power radio small antenna. This is also a lot of friends use the hand-feeder bar antenna The effect is also good.
If you really care less about power than a test, the output of the transmitter is not connected to the coaxial cable, but to the 380V power cable. The same number of meters, the power cable loss must be very small, because the power = current * voltage, power The small internal resistance of the cable will share little voltage on the cable, and the small power loss will be small. However, the high-frequency signal is the skin effect propagation. The power cable cannot transmit high-frequency signal loss. It will be quite large. It can be said that a little common sense friends know that Power cables cannot be used as feeders. From this point it is also proved that looking at power alone is totally wrong.
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