0
\$\begingroup\$

I'd like to ask for help with conversion of measured voltage V=10dBμV to dBm units. Voltage is measured on frequency f=0.33 GHz (measured with spectral analyser). I've found some sheets with bunch of formulas for calculations with Electromagnetic compatibility, but wasn't successful to find out, how to include frequency into that formulas. Thank you very much for help.

\$\endgroup\$
4
  • 1
    \$\begingroup\$ 0dBuV = 1uV, voltage. 0dBm = 1mW, power. So no straight conversion. \$\endgroup\$
    – user76844
    Sep 18, 2018 at 16:21
  • \$\begingroup\$ If you know Z= 50 then you can convert Voltage to power , which I assume you can calc. , but if dBuV is an Rx high impedance input, then you cannot use 50 Ohms. \$\endgroup\$ Sep 18, 2018 at 16:30
  • \$\begingroup\$ To make the conversion, you need to know the impedance of the load on the signal. Spectrum analyzers are usually 50 ohms. From the voltage on the load (in microvolts) you can calculate the power in watts, then from there to dBm is easy. \$\endgroup\$
    – JRE
    Sep 18, 2018 at 16:32
  • \$\begingroup\$ video uses 75 ohms; audio systems use 600 ohm; what is your system impedance? \$\endgroup\$ Sep 18, 2018 at 16:52

1 Answer 1

4
\$\begingroup\$

The "dBm" is a unit of power where 0 dBm = 1 milliwatt. The dB\$\mu\$V is a unit of voltage where 0 dB\$\mu\$V is 1 microvolt. If you know the resistance of the circuit (often called the impedance) you can convert 10 dB\$\mu\$V to 3.162 \$\mu\$V and square it then divide by resistance (often 50 \$\Omega\$) to get power.

So assuming the resistance is 50 \$\Omega\$, 3.162 \$\mu\$V produces a power of 0.2 picowatts and this converts to -97 dBm.

how to include frequency into that formulas.

It isn't included unless you are leaving some important information out of your question.

\$\endgroup\$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.