How to convert dB into Magnitude and Angle

[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).

 

[pancho_hideboo]

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

Mag = 10^(dB/20)

 

[KlausST]

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]

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

 

[pancho_hideboo]

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.

 

[chuckey]

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

 

[pancho_hideboo]

The followings are MATLAB code for dbv()=db20() and dbp()=db10().

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)));

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://edadocs.software.keysight.com/display/ads2009/db()+Measurement
https://en.wikipedia.org/wiki/Decibel

 

[tggzzz]

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".

 

[KlausST]

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

 

[tggzzz]

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".

 

[KlausST]

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

 

[pancho_hideboo]

Consider original point of this thread.

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

For example, consider S-parameter of Touchstone format
There are following three styles for complex value.
(1) dB/Angle
(2) Mag/Angle
(3) Real/Imag
Here Mag=10^(dB/20)

https://edadocs.software.keysight.com/display/ads2009/db()+Measurement
https://www.edaboard.com/threads/344348/

 

[KlausST]

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

 

[pancho_hideboo]

Is "magnitude" always considered to be voltage or current?

Yes.

Can´t it be power?

It can not be.
S-Paremeters are defined by Sqrt(complex power value).
This is a reason why db() is defined as db20() in Agilent(Keysight) ADS.
https://edadocs.software.keysight.com/display/ads2009/db()+Measurement

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

 

[KlausST]

Hi,

The OP says nothing about S parameters nor Agilent (Keysight) ADS.

Klaus

 

[pancho_hideboo]

The OP says nothing about S parameters nor Agilent (Keysight) ADS.

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.

 

[KlausST]

Hi,

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

Klaus