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Design Notes

Amp-Mixer SSB NF and RFI Spectrum Measurements

This project demonstrates the use of SSB NF measurements in VSS as well as the spectrum measurement in RFI.


The system diagram titled Amp Mixer VSS is set up to measure the NF and Spectrum of this system.  In order to obtain the same results from a basic spreadsheet calculation of NF, we illustrate the need for the BPF to reject the image noise.  Many RF system designs are SSB due to concerns for interference in the image band.  DSB NF can easily be simulated in VSS as well.  However, the spreadsheet calculation must be set up to track both the desired and image noise.  If the BPF is disabled, the system will be DSB and the NF will increase by nearly 3 dB.  A proper spreadsheet calculation will show this as well.

Measurements and Results

The Graph titled Amp Mixer NF shows a single data point at 0.23 GHz, the output frequency of the Amp Mixer system.

The Amp Mixer Spectrum graph compares VSS and RFI results.

RFI measurements are found on the "RF Inspector" node under "System" measurements.  Here, we are displaying a power spectrum calculation on the red trace.  Note that if you click/hold the mouse on the VSS (magenta) trace, you get a display of frequency and power.  On the RFI (red) trace, however, a click/hold produces a display of frequency, power, and also information on where the frequency product came from.  Further, if you double-click on the RFI (red) trace, you will get an interactive display that allows you to explore detailed information on exactly where each tone comes from.

System Diagram - Amp Mixer VSS

Graph - Amp Mixer NF

DB(C_NF(TP.Input,TP.Output,1,1,0,0)) (GHz) Amp Mixer VSS Frequency DB(C_NF(TP.Input,TP.Output,1,1,0,0)) Amp Mixer VSS Cascaded Noise Figure, Ideal, Cumulative, dB
0.23 2.75204

Graph - Amp Mixer Spectrum