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?

 

[Easy peasy]

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

so 100uV = 0.1mV = 40 dBuV

so 1000uV = 1mV = 60dBuV

 

[FreshmanNewbie]

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?

 

[Easy peasy]

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

--- Updated Jul 17, 2024 ---

voltage levels are absolute, and expressed in dBuV

 

[KlausST]

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

 

[albbg]

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