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# How do I include Mismatch Uncertainty into the N5531S Measuring Receiver Absolute Amplitude accuracy?

The N5531S Measuring Receiver System is comprised of a PSA Series Spectrum Analyzer with Option 233 (measuring receiver personality), a P-Series or an EPM Series Power Meter, and an N5532B (or N5532A) Sensor Module.

1. Convert the N5531S Absolute Amp Spec to Linear value.
2. Divide by the coverage factor (K = 2.57) to get 1 sigma.
3. Calculate the Source Mismatch error (1 sigma).
4. RSS the Abs Amp and Mismatch terms.
5. Multiply by the appropriate coverage factor (K).
6. Convert the Linear result to dB.

Source Mismatch Calculation Example
Assume we are measuring a 2 GHz, 0 dBm signal. The N5531S Absolute Amplitude Accuracy is ± 0.190 dB. The Sensor Module VSWR is 1.28:1 (rho = 0.122). Assume the source VSWR is 1.5:1 (rho = .2).

1. Convert Abs Amp to linear (%): 100 x [ 10^(0.190/10) -1] = 4.47%
2. Normalize to 1 Sigma (K= 2.57): 4.47%/2.57 = 1.74%
3. Determine Mismatch error: 100% x (0.2) x (0.122)/Sqrt(2) =1.73%
4. RSS the terms: Sqrt [ (1.74)^2 + (1.73)^2 ] = 2.45%
5. Multiply by the appropriate coverage factor (K): 2.57 x 2.45% = 6.30 %
6. Convert % to dB: dB = 10 x Log[ 1 + (6.30/100)] = ± 0.265 dB