How is the magnitude in dBm calculated in Moku:Lab’s Frequency Response Analyzer?
Written by Paul Cracknell
Updated at February 5th, 2021
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Moku:Go
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The Frequency Response Analyzer (FRA) provides response plots of magnitude and phase. While the phase is expressed in degrees, the magnitude is expressed in terms of dBm power. This is a log scale of power expressed in dB relative to 1 milliWatt.
How is this magnitude in dBm calculated in Moku:Lab’s FRA?
Let us take a simple example. We will set the swept sine wave output of the FRA to 1 Vpp, configure 50 Ω input and output impedance, and, for this example, a sweep from 10Hz to 1kHz. Then with a coax cable connecting output 1 of the Moku:Lab to input 1, we run a sweep of the FRA. You should see a flat amplitude response at 4.0 dBm.
How is the 4.0 dBm is calculated?
It comes from this formula (valid for sinusoidal signals):
