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# How to convert dB into Magnitude and Angle

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#### narayani

Dear Sir,

I want to convert 18.65 dB into its Magnitude and Angle (Phase). Can you give formula to converting dB into its equivalent magnitude and angle (Phase).

You can never get phase infomation from dB.
You can only get magnitude infomation.

Mag = 10^(dB/20)

narayani

### narayani

Points: 2
Hi,

dB is a value of ratio.

For values like voltage, current the above formula is correct.

For value like power "Mag = 10^(dB/10)" is correct.

Klaus

narayani

### narayani

Points: 2
then how to convert dB into Magnitude and phase. How to get phase values for dB.

I have following definition in Verilog-A code.

define db20_real(x) (pow(10, (x)/20))
define db10_real(x) (pow(10, (x)/10))

then how to convert dB into Magnitude and phase. How to get phase values for dB.
Again, You can never get phase infomation from dB.

narayani

### narayani

Points: 2
Do you read the replies? dBs are like percentages %, a ratio of two numbers. Nothing about phase angles at all!!
Frank

The followings are MATLAB code for dbv()=db20() and dbp()=db10().
Code:
function y=dbv(x)
% dbv(x) = 20*log10(abs(x)); the dB equivalent of the voltage x
y = -Inf*ones(size(x));
if isempty(x)
return
end
nonzero = x~=0;
y(nonzero) = 20*log10(abs(x(nonzero)));
Code:
function y=dbp(x)
% dbp(x) = 10*log10(x): the dB equivalent of the power x
y = -Inf*ones(size(x));
if isempty(x)
return
end
nonzero = x~=0;
y(nonzero) = 10*log10(abs(x(nonzero)));

Again, You can never get phase infomation from dB value, even if you use MATLAB or ANY.

https://en.wikipedia.org/wiki/Decibel

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Hi,
dB is a value of ratio.
For values like voltage, current the above formula is correct.
For value like power "Mag = 10^(dB/10)" is correct.

Not quite. The Bel is always a power ratio, by definition. A deciBel is 1/10 of a Bel, hence the "10" in the well-known formulae.

Since power is proportional to the square of the voltage, expressing voltage ratios in dB introduces an extra "2", hence the "20".

Hi,

Not quite.

The Bel is always a power ratio, by definition. A deciBel is 1/10 of a Bel, hence the "10" in the well-known formulae.

Since power is proportional to the square of the voltage, expressing voltage ratios in dB introduces an extra "2", hence the "20".

Isn´t that what i wrote? At least i wanted to..

Klaus

Hi,

Isn´t that what i wrote? At least i wanted to..

Klaus

The end result is the same, but your explanation implied there was a difference for power and voltage, whereas there is no difference.

Sorry that it is so difficult to follow what we are discussing; by design this website strips out the context, hence the large amount of vertical whitespace between "Hi" and "Isn't".

Hi,

The end result is the same, but your explanation implied there was a difference for power and voltage, whereas there is no difference.

Yes, there is a difference. And you explained it correctely already.

1) for voltage: dB(U) = 20 * log(U_out / U_in)

2) for power: dB(P) = 10 * log(P_out / P_in)

the mathematical calculation is like you explained:

Klaus

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Hi,

Consider original point of this thread.

Decibel definition should be db20() not db10() for this thread point.

I read the original post and can´t find this.

Is "magnitude" always considered to be voltage or current? Can´t it be power?

Klaus

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Hi,

Klaus

Phase(Angle) is refered in this thread, so it is voltage not power.

Again, Decibel definition should be db20() not db10() for this thread point.

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Hi,

Yes, here it is. The OP knows how to hide informations...

Klaus

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