Explanation of the meanings of units of measurement such as dBm, dBV, dBuv, dB, dBf
The significance of dB
1. dB is basically a proportional value, which is a multiple of the unit of expression. This is the relative difference between the test data and the reference standard.
2. Calculated: dB = 10 log (P1/P2) = 20 log (V1 / V2) V1 is the test data and V2 is the reference standard. For example, V1 data is 2 times that of V2, which is 6 dB. (P stands for power, V stands for voltage)
3. The word behind the dB is the unit value used as a reference standard. For example, dBV is the measured V1 data when the reference standard V2 = 1V. That is the meaning of 6 dBV = 2V.
4. Conversely, if the value of V1 is less than V2, the dB value becomes negative. In other words,
dB conversion formula (algorithm that engineers must understand)
1. 1 dB = 1.1x, 2 dB = 1.25x, 3 dB = 1.4x, 6 dB = 2x, 10 dB = 3x, 20 dB = 10x, and 30 dB = 30x. Others can be converted with the above values ​​without difficulty. (Conversely - 6 dB is 1/2 = 0.5)
2. To grasp a principle in the conversion, the addition of the dB value is equal to the multiplication of the multiple.
For example: 40 dB = 20 dB + 20 dB = 10 * 10 = 100 times
For example: 56 dB = 20 dB + 30 dB + 6 dB = 10 * 30 * 2 = 600 times
Audio unit of audio measurement unit ----- The common example is AC micrometer AC millimeter
1. The basic unit of measurement is AC Vrms, which is the AC mean voltage. Normally mV and V. (1 V = 1000 mV)
2. There are usually two black scale dBV and red dBm scale indicators. (dBV is not commonly used now)
3. dBV is a 0 dB reference standard with 1 V, and dBm (dBmW) is a 0 dB reference standard with 1 mW (0.775 V).
4. The audio standard impedance is nominally 600 Ohm, so 1 mW is equivalent to 0.775 V (775 mV).
5. Take the display on the microvoltmeter as an example: 300 mV = - 10 dBV = - 7 dBm
Measurement Units for RF RF Instruments - A common example is the RF Signal Generator RF Signal Generator
1. The basic unit of measure is uV, mV, dBuV or dBm. (1 mV = 1000 uV)
2. UAV and mV units have been used less because of the wide range of signal strength changes.
3. dBuV is a 0 dB reference standard at 1 uV. (In general, the signal strength dB or dBu is actually dBuV)
4. dBm (dBmW) Same as above, with 0m reference at 1mW, but the standard impedance of the RF is set to 50 Ohm, so 0 dBm is 0.224 V, which is equivalent to 107 dBuV. (224000 uV)
5. Take the output display of the signal generator as an example: 60 dBuV = - 47 dBm = 1000 uV = 1 mV
Other related matters needing attention
The output of the signal generator has a difference between Open and Load types, which means that the output value will have a 6 dB difference. (When there is EMF, its value is no-load value, indicating that the actual output will be attenuated by 6 dB after the output load)
New sensitivity test unit dBf description
In the past, the sensitivity of FM radio was marked using uV. It was only recently discovered how suddenly the directory became dBf. What is this stuff? Finally figured out that this is the latest sensitivity test unit.
The original uV was later evolved to dBu, which is dBuV. Again, the dBm on the instrument is the dBmW dB value for 1mW. The latest is dBf which is the dB value for femtowatt (10th-15th power).
The past dBu or dBm (50 ohm) is the absolute value of the voltage, independent of the impedance. (Although the dBm should be related to the impedance, but everyone is set to 50 ohm as the standard)
dBf is the voltage uV value according to the antenna input impedance of 75 ohm or 300 ohm converted to femtowatt, and then take the dB value. Therefore dBf
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