DBmV and Its Applications

We define 0 dBmV as 1 mV across 75 Q impedance. Note that 75 Q is the standard impedance of CATV, coaxial cable, and TV sets. From Appendix A, the electrical power law, we have

where Pw is the power in watts, E the voltage in volts, and R the impedance, 75 Q. Substituting the values from above, we obtain

Pw = (0.001)2/75 0 dBmV = 0.0133 x 10-6 W or 0.0133 |W

By definition, then, 0.0133 W = +60 dBmV

If0 dBmV = 0.0133 x 10-6 Wand0 dBm = 0.001 W,andgainindB = 10 log(P1 /P2), or, in this case, 10 log[0.001/(0.0133 x 10-6)], then 0 dBm = +48.76 dBmV.

Remember that, when working with dB in the voltage domain, we are working with the E2/R relationship, where R = 75 Q. With this in mind the definition of dBmV is voltage in mV

If a signal level is 1 V at a certain point in a circuit, what is the level in dBmV? dBmV = 20 log (1000/1) = +60 dBmV. If we are given a signal level of +6 dBmV, to what voltage level does this correspond? +6 dBmV = 20 log(XmV/1 mV).

Divide through by 20:

These signal voltages are rms (root mean square) volts. For peak voltage, divide by 0.707. If you are given peak signal voltage and wish the rms value, multiply by 0.707.

Was this article helpful?

0 0

Post a comment