Net Power: Difference between revisions

Latest revision as of 20:43, 20 January 2009

Net Power is defined as Forward Power minus the Reflected Power. This document describes the formula's that should be used to correctly calculate the Net Power.

The Net power always has to be calculated in linear power values. It is not possible to calculate the Net power directly from logarithmic values (dBW, dBm, dBpW, ...) without converting them to linear power values.

The following formulas should thus be used:

Failed to parse (SVG (MathML can be enabled via browser plugin): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle P[W] = 10^{\frac{P[dBW]}{10}}} or Failed to parse (SVG (MathML can be enabled via browser plugin): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle P[mW] = 10^{\frac{P[dBm]}{10}}}

Formula -1: Logarithmic power value to linear power value

Failed to parse (SVG (MathML can be enabled via browser plugin): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle P_{net}[W] = P_{fwd}[W] - P_{refl}[W]}

Formula -2: Net power calculation from forward and reflected power

Failed to parse (SVG (MathML can be enabled via browser plugin): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle P[dBW] = 10 * ^{10}log(P[W])} or Failed to parse (SVG (MathML can be enabled via browser plugin): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle P[dBm] = 10 * ^{10}log(P[mW])}

Formula -3: Linear power value to logarithmic power value

Failed to parse (SVG (MathML can be enabled via browser plugin): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle P[dBm] = P[dBW] + 30}

Formula -4: dBW to dBm

Example[edit]

Let's assume that on a certain frequency (for example: 201,973 MHz), a forward power of 50 dBm is measured, with a reflected power of 30 dBm.

First the power values should be calculated from dBm values to linear values.

Failed to parse (SVG (MathML can be enabled via browser plugin): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle 50 \ dBm = 10^{\frac{50}{10}} \ mW = 100.000\ mW = 100\ W}

${\displaystyle 30\$

Then the net power should be calculated by subtracting the linear values

Failed to parse (SVG (MathML can be enabled via browser plugin): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle P_{net} = P_{fwd}[W] - P_{refl}[W] = 100\ W - 1\ W = 99 \ W}

And the linear value should be converted to a dBm value again:

Failed to parse (SVG (MathML can be enabled via browser plugin): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle P[dBW] = 10 * ^{10}log(99 W) \approx 19,95635195 \ dBW \approx 49,95635195 \ dBm}

The Net Power of 50 dBm forward and 30 dBm reflected power is thus 49,96 dBm.

@@ Line 1: / Line 1: @@
-[[Net Power]] defined as [[Forward Power]] minus the [[Reflected Power]]
+[[Net Power]] is defined as [[Forward Power]] minus the [[Reflected Power]]. This document describes the formula's that should be used to correctly calculate the [[Net Power]].
-This document describes how you should calculate the [[Net power]] correctly.
-{| border=1
+The [[Net power]] always has to be calculated in linear power values. It is not possible to calculate the [[Net power]] directly from logarithmic values (dBW, dBm, dBpW, ...) without converting them to linear power values.
-|+ '''''Given information'''''
-|-
-! Frequency (MHz)
-! Forward Power (dBm)
-! Reflected Power (dBm)
-|-
-! 201,973 || 50 || 30
-|}
-'''Question:''' What is the Net Power?
+The following formulas should thus be used:
-'''Answer:''' 141,8144768 mA
+<math>P[W] =  10^{\frac{P[dBW]}{10}}</math> or <math>P[mW] =  10^{\frac{P[dBm]}{10}}</math>
-== The calculation ==
+{{Formula||1|Logarithmic power value to linear power value}}
-First you calculate the dB difference in power.
-<math>35,4 - 35,1 = 0,3\ dB</math>
+<math>P_{net}[W] = P_{fwd}[W] - P_{refl}[W]</math>
-*'''Note:''' the unit is dB not dBm
+{{Formula||2|Net power calculation from forward and reflected power}}
+<math>P[dBW] = 10 * ^{10}log(P[W])</math> or <math>P[dBm] = 10 * ^{10}log(P[mW])</math>
-Calculate the calibrated current to dBmA so we can add the value.
+{{Formula||3|Linear power value to logarithmic power value}}
-<math>20 * log10(137) \approx  42,73441134 \ dBmA</math>
+<math>P[dBm] = P[dBW] + 30</math>
+{{Formula||4|dBW to dBm}}
-So after the addition of the power difference the new value is 43,03441134 dBmA.
+== Example ==
+Let's assume that on a certain frequency (for example: 201,973 MHz), a forward power of 50 dBm is measured, with a reflected power of 30 dBm.
-Calculate this back to mA:
+First the power values should be calculated from dBm values to linear values.
-<math>10^{\frac{43,03441134}{20}} \approx  141,8144768 \ mA</math>
+<math> 50 \ dBm = 10^{\frac{50}{10}} \ mW = 100.000\ mW = 100\ W</math>
+<math> 30 \ dBm = 10^{\frac{30}{10}} \ mW = 1000\ mW = 1\ W</math>
+Then the net power should be calculated by subtracting the linear values
+<math>P_{net} = P_{fwd}[W] - P_{refl}[W] = 100\ W - 1\ W = 99 \ W</math>
+And the linear value should be converted to a dBm value again:
+<math>P[dBW] = 10 * ^{10}log(99 W) \approx  19,95635195 \ dBW \approx  49,95635195 \ dBm</math>
+The [[Net Power]] of 50 dBm forward and 30 dBm reflected power is thus 49,96 dBm.
 [[Category:RadiMation]]
 [[Category:Calculation]]

Net Power: Difference between revisions

Latest revision as of 20:43, 20 January 2009

Example[edit]

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