Find the RF Interference Power and Impact on Receiver Sensitivity

Updated Apr 27, 2023



  • PXI Vector Signal Transceiver
  • PXIe-5841
  • PXI Controller
  • PXI Chassis


  • RFmx
  • RFmx SpecAn
  • RFmx Waveform Creator



Operating System

  • Windows

In wireless system, RF interferences are found any where at any time, the in band RF interference can not be filter out and will cause noise rise to receiver system which will degrade the receiver sensitivity. To accurately test the system capability such as data rate or throughput, it is required and important to find the exact RF interference signal power level and find its impact on receiver sensitivity.
This article discusses the basic Method of Procedure on how to find the RF interference signal power level even if it is lower than the noise floor of the Vector Signal Transceiver (VST). We configure the Vector Signal Generator (VSG) to create a RF signal for emulating RF interference signal, and loop it back to Vector Signal Analyzer (VSA).  Refer to below for block diagram, consider PXIe-5841 as an example:
Picture -1.JPG
The procedure of measuring RF interference signal power level is summarized as below:

  • Record the VSA noise floor with a 50Ω dummy load connected to RF input port

  • Record the displayed total channel power include noise power and interference power

  • Calculate the interference signal power with this formula CPinterf_measured  = 10 x Log (10CPSA_display/ 10) - 10CPSA_noise/ 10) )  

CPinterf_measured is the measured Interference Channel power
CPSA_display is the displayed signal analyzer (SA) Channel power
CPSA_noise is the signal analyzer (SA) Noise floor

The intended audiences are NI-VST users who have good knowledge of RF interference, and familiar with NI tools such as RFmx, RFSA, RFSG.

Measure RF Interference Signal Power

  1. Record the VSA noise floor
To measure the RF interference signal power, we need to measure and record the VSA noise floor before input simulated RF interference signal from VSG to VSA. Best practice is to connect a dummy load at VSA input port. In this article, as an example, the measured VSA noise floor CPSA_noise is -67.34dBm in 98.3MHz bandwidth. Refer to below screen shoot for the measure noise floor:
Noise floor.JPG
  1. Generate the simulated RF interference signal from VSG with below configurations:
  • Center frequency: 3.5GHz
  • Bandwidth: 98.3MHz
  • Power setting at VSG: -70dBm
  • Jumper cable loss: 1dB estimated
  • Power input to VSA: -71dBm
  1. Read the displayed power of -65.81dBm in VSA, shown below:
Noise Displayed.JPG
  1. Calculate the simulated RF interference power level (CPinterf_measured) with the formula discussed in overview section
CPinterf_measured  = 10 x Log (10(-65.81/ 10) - 10(67.34/ 10) )  = -71.08dBm which is very close to the actual input power of -71.00dBm
  1. Calculate more simulated RF interference power levels (CPinterf_measured) for other displayed power values (CPSA_display)
  • Apply the formula shown in overview section and refer to table below for more values of calculated RF interference power
  • Noticed the last row of the table, the displayed power level (CP SA_display) is some 3 dB higher than either the measured interference power level (CP interf_measured) or the SA noise floor (CP SA_noise) because both are around -67.30dBm, two equal power RF signal add up increase the power by 3dB.
Table 1.JPG
You can apply the above described method to find the RF interference signal power for other frequencies and bandwidths. 

RF Interference Impacts On Receiver Sensitivity

  1. RF interference impacts on receive sensitivity is quantified with receiver sensitivity degradation (RSD) is calculated with the formula NR = RSD = 10 x log (1+10(ΔP/10))                                (2)
NR is the noise rise which is equal to RSD
RSD is the sensitivity degradation
ΔP is ratio of noise floor to interference level
Some calculations from formula (2) shown in below table, noticed the last row of the table, where ΔP = 0dB which means the interference equal to the original noise floor, hence the new noise floor rises 3dB.
Table 2.JPG
For wireless system, it is a commonly acceptable that the sensitivity degradation is limited to some 0.4dB which means the interference level should be 10dB lower the receiver sensitivity.