dBm, µV, dBµV, mV, dBmV Basics: What Are They & How To Convert Between Them?

‘Note: This is an article written by an RF engineer who has worked in this field for over 40 years. Visit ABOUT to see what you can learn from this blog.’

If you are working with a receiver, then you must clearly understand the basic knowledge mentioned in this article.

You need to know all basics of dBm, µV, dBµV, mV, and dBmV, and how to transfer them between each other without difficulty.

If you already know them well I would suggest you to quickly go through this post to see if there is anything new to you. If you are still struggling with these terms, then you should read this post word-by-word and make sure you really understand them.

Before starting reading this article, you should read these two very helpful posts first:

While discussing these 4 terms, dBm, µV, dBµV, and dBmV, we will focus on very small signal strength for receiver design.

For a typical receiver, the received signal is very weak and the most popular range is between 0.2µV and 10 mV. Therefore, for the sake of convenience, knowing how to use dBm, µV, dBµV, mV and dBmV is a necessity.

dBm is also equally useful in transmitter design and we have discussed this term in a separate article.

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  • dBm (Decibel relative to 1mW power level), one of the most-used terms in RF field.

dBm is simply power measured relative to 1 milliwatt (1mW), therefore, it is an absolute value and has its unit..

‘1 mW is 0 dBm as a reference.’  0 dBm = 1 mW

Visit this post for more information about dBm.

 

  • µV (microvolt), dBµV (dB over 1 microvolt) , mV (millivolt) and dBmV (dB over 1 millivolt).

1 µV = 1.00E-06 V

0 dBµV = 1 µV

1 mV = 1.00E-03 V

0 dBmV= 1 mV

How to convert these units?

These all represent the signal strength sourced from a signal generator or received by the antenna.

dBm (dB over 1 milliwatt) is power and µV is voltage, they are different units so we need to know their relationship before converting them.

We need to know the source or load resistance so we can use this basic equation:

\(P=V^2/R\)

Where P is the power in watts, V is the RMS (root mean square) voltage in volts, and R is the resistance in ohms.

Most RF application (I would say more than 95%) has 50 ohms as resistance for the reason of consistency and convenience.

Since 0 dBm = 1 mW = 0.001 W

\(0.001=V^2/50\text{      and      } V^2=0.001\times 50=0.05\)

\(\text {Therefore,  }V=0.224V=224 mV=2.24\times 10^5 µV\text{,   (0 dBm)}\)

And we can say 0 dBm is equivalent to 0.224 Vrms with 50 ohms of impedance (resistance).

However, o dBm is a very high level and is not a typical received signal  for a receiver.

As we mentioned earlier in this article, the most popular receiver signal is between 0.2µV and 100 mV, so our examples will focus on the conversion in this range.

Examples:

We assume the resistance is 50 ohms in all cases.

1.  If a signal generator output level is 2.24 mV, how many dBm is it equivalent to?

Step 1, we need to know how many watts this signal is:

\(2.24 mV=0.00224V\)

\(\text {So  }P=V^2/50=0.00224^2/50=0.0000001W=0.0001mW\)

\(\text{And  }10log(0.0001mW/1mW)=-40 dBm\)      Ans.

 

2.  If the received signal is -95 dBm, what is the µV, dBµV and dBmV level?

Step 1, we need to know how many milliwatts is -95 dBm:

\(10log(P/1mW)=-95\)

\(P=10^{-95/10}=3.16\times 10^{-10}mW=3.16\times 10^{-13}W=V^2/50\)

\(V=\sqrt{50\times P}=\sqrt{50\times 3.16\times 10^{-13}}=3.97\times 10^{-6}volts=3.97µV\)    Ans.

\(20log(3.97µV/1µV)=12dBµV\)    Ans.

\(\text{And   }20log(3.97µV/1mV)=20log(0.00397)=-48dBmV\)    Ans.

 

Read through these 2 examples and make sure that you really understand each step of them and can convert them without any difficulty.

If you are ready here are 2 more questions for you to practice:

Q1:   How many dBm is 112 µV equivalent to, and how many dBµV is it?

Ans.   -66 dBm & 41 dBµV.

Q2:   How many dBµV is -84 dBm?

Ans.   23 dBµV.

In the 2nd 20 years of my carer, I almost only use dBm as the power reading and basically disregard all other terms mentioned in this article. You will find out this is true for you also, once you get deeply involved in RF.

However, you should know all these terms and can convert them without any difficulty.

If you are still confused with dB, dBm, dBc, etc. these 2 articles can help you out:

 

I hope you will find the table below helpful:

 

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