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20mV to dbuV conversion.....
- Thread starter mishra87
- Start date
According to this: https://www.softwright.com/knowledg...dbu-dbm-dbuv-and-other-field-intensity-units/
your formula is incomplete.
your formula is incomplete.
(7) E(dBµV) = E(dBµV/meter) + Gr(dBi) - 20log f(MHz) + 29.8
Thank you very much !!!
dBμV/m is the clue that is a field strength calculation.
Consider how you would calculate the change in decibels between two voltage values. Suppose that value A is the reference level, and value B is the new value; then,
\(20 \log_{10}(\frac{B}{A}) \; \text{dB}\)
In other words, to find the value in dB, we take the base-10 logarithm of the ratio of the new value to the reference value.
Notice that units of "naked" dB are always relative: they are the ratio of one value to another. However, by convention, several absolute dB units have been defined by making their reference (the A value in the example above) fixed.
In the old telephone days, circuits were designed to be terminated by 600 Ω loads (this helped maximize power transfer across long copper runs by ensuring matched impedances). In this system, a convenient unit of power was the milliwatt, and so it made sense to define a voltage reference level that corresponded to the level of voltage required to deliver 1 mW of power to a 600 Ω load. If you do the arithmetic, you'll see that this RMS voltage is
\(0 \; \text{dBu} = \sqrt{0.6} \approx 0.775 \text{V}\)
Now, knowing that 0 dBu = 0.775 V, we can convert 20 mV = 0.02 V to the dBu scale:
\(20 \log_{10}(\frac{0.02}{0.775}) \approx -31.765 \; \text{dBu}\)
In English, this says is that 20 mV with respect to 0.775 V is nearly -32 dB. But since we used the established reference that corresponds to dBu, we can express it as such. Anyone in the world who knows that 0 dBu = 0.775 V can take that -32 dBu number and calculate that it equals 20 mV.
NB: If the 20 mV is not an RMS value, it must first be converted to RMS.
\(20 \log_{10}(\frac{B}{A}) \; \text{dB}\)
In other words, to find the value in dB, we take the base-10 logarithm of the ratio of the new value to the reference value.
Notice that units of "naked" dB are always relative: they are the ratio of one value to another. However, by convention, several absolute dB units have been defined by making their reference (the A value in the example above) fixed.
In the old telephone days, circuits were designed to be terminated by 600 Ω loads (this helped maximize power transfer across long copper runs by ensuring matched impedances). In this system, a convenient unit of power was the milliwatt, and so it made sense to define a voltage reference level that corresponded to the level of voltage required to deliver 1 mW of power to a 600 Ω load. If you do the arithmetic, you'll see that this RMS voltage is
\(0 \; \text{dBu} = \sqrt{0.6} \approx 0.775 \text{V}\)
Now, knowing that 0 dBu = 0.775 V, we can convert 20 mV = 0.02 V to the dBu scale:
\(20 \log_{10}(\frac{0.02}{0.775}) \approx -31.765 \; \text{dBu}\)
In English, this says is that 20 mV with respect to 0.775 V is nearly -32 dB. But since we used the established reference that corresponds to dBu, we can express it as such. Anyone in the world who knows that 0 dBu = 0.775 V can take that -32 dBu number and calculate that it equals 20 mV.
NB: If the 20 mV is not an RMS value, it must first be converted to RMS.
My bad, I hadn't heard of dBuV before and mistakenly read it as dBu.
(BTW, dBu is still very much in use in audio engineering.)
OK, Abolish the transmission unit.The decibel originates from methods used to quantify signal loss in telegraph and telephone circuits. The unit for loss was originally Miles of Standard Cable (MSC). 1 MSC corresponded to the loss of power over a 1 mile (approximately 1.6 km) length of standard telephone cable at a frequency of 5000 radians per second (795.8 Hz), and matched closely the smallest attenuation detectable to the average listener. The standard telephone cable implied was "a cable having uniformly distributed resistance of 88 Ohms per loop-mile and uniformly distributed shunt capacitance of 0.054 microfarads per mile" (approximately corresponding to 19 gauge wire). MSC replaced in 1924 with the name TU for "transmission unit"
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