Continue to Site

# EMC reports dB

#### FreshmanNewbie

I have a question on EMC reports.

When there's a graph, as shown in this link (https://emcfastpass.com/emc-testing-beginners-guide/emissions/), just above CE limits.

Which are the signals that are being compared to arrive at a dB value? As I understand that, dB has no units. Just a number.

So, which are the 2 signals that are being compared to give a dB peak?

Wow, dBuV or dBuV/m are dB relative to 1uV or 1uv / m

so 100uV = 0.1mV = 40 dBuV

so 1000uV = 1mV = 60dBuV

Wow, dBuV or dBuV/m are dB relative to 1uV or 1uv / m

so 100uV = 0.1mV = 40 dBuV

so 1000uV = 1mV = 60dBuV
I was asking like, which 2 signals are in question while measuring?

Suppose, I see a peak at, say 50MHz. Obviously, the peak signal at 50MHz is from the PCB in question. With respect to what signal is this 50MHz being measured and given in dB?

you just don't get it - do you ? - read post #2 again - but very slowly . . . .
--- Updated ---

voltage levels are absolute, and expressed in dBuV

Last edited:

One thing:
In oppostite to your post, the unit is NOT "dB" in this case, it is "dBuV" (or similar).

The other thing:
You are free to do an internet search on your own: "what does dBuV mean" (or similar) .. or ask chatGPT

Klaus

As you said "dB" is the measurement of a quantity of a signal (eg.: power, voltage, electric field intensity, ec.) referred to a second signal, that is a relative measurement.

power dB = 10*Log(P1/P2)
voltage dB = 20*Log(V1/V2)
E field: dB = 20*Log(E1/E2)

In order to have an absolute value, using the log scale of the dB, the seconde (reference) signal P2 or V2 or E2 can be fixed to a standard value. For instance we have the following standard measurement units:

power: dBm = 10*Log(Plinear/1mW)
voltage: dBuV = 20*Log(Vlinear/1uV)
E field: dBuV/m = 20*Log(Elinear/1uV/m)

There are many others