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Resistive Attenuator Measurement Using DC

Posted: Tue Mar 12, 2019 5:00 pm
by mediatechnology
I needed to quickly check the accuracy of a 60 dB balanced U-pad for the MC preamp.

The source resistance for the test needed to be 3.3Ω making the legs around 1620Ω each.

Rather than use an AC generator at 0 dB or some elevated level and then risk reading error from AC noise I decided to use DC.
I can read DC with more precision and greater measurement confidence.

I applied 10.003V to the pad and read the shunt voltage as 10.2 mV.
That's -59.83 db relative to 10V DC.
The calculated attenuation, with ideal resistors, is -59.849 dB.
Close enough.

A little-known fact is that the dB function on the Fluke 8050A works on the DC scale.
The relative function also works when reading "DC dB."
When read as "DC dB" the attenuation read -59.85 dB.