Frequency Response Analyzer
By default, each channel shows the ratio of the input to the output, In / Out. This is useful for measuring the transfer function of a device under test. The math channel allows you to plot different combinations of Ch 1 and Ch 2. If the output amplitudes of both channels are set to the same value, then viewing the math channel as Ch 1 / Ch 2 will show the ratio In 1 / In 2, since the outputs are the same.
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 1Vpp, 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):