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CAIA 070724A: Induced Noise in Oscilloscope Cabling

Induced Noise in Oscilloscope Cabling

CAIA Technical Report 070724A

Adam Black
July 24, 2007


Several experiments we conducted recently at CAIA involved measuring voltage waveforms using a Digital Storage Oscilloscope and BNC-to-banana plug cables. In this report we will consider whether some BNC-to-banana cables receive more external noise than others.


The experiment was set up using the following equipment:


To test the noise induced in the BNC-to-banana plug leads we picked a cable shown in Figure 2, connected the BNC end into channel four of the oscilloscope and connected the banana plug ends together, hence short-circuiting the cable to the oscilloscope's ground. We then recorded 2500 voltage samples of channel four and stored the values on a PC, for post processing. The measurements were repeated for all six cables. During the experiments the oscilloscope was configured with a vertical resolution of 5 mV/div and timebase of 25 milliseconds.

BNC to banana plug cable

Figure 1 - BNC-to-banana plug cable

Cables used for the experiments

Figure 2 - Comparison of the cables used for the experiments.


Figures 3 and 4 show the range of voltages seen by the oscilloscope when cables one to six were used. The Probability Density Functions and Cumulative Density Functions show the distribution of voltage levels measured on channel four. When evaluating these graphs a large spread of voltages from the origin indicates that lots of noise was being measured, while a small spread of values from the origin indicates a small amount of noise was measured in the system.

We can see from Figure 3 and 4 that cables 1, 3, 4 and 6 appear to introduce the least amount of noise, while cables 2 and 5 introduce the most noise. Referring to Figure 2 and the graphs above, we can conclude that the cables which receive the most external noise have a long unshielded length, and the cables which recieve the least amounts of noise have a shorter unshielded length.


We confirmed that cables with longer unshielded sections receive more external noise than cables with shorter unshielded sections.

Last Updated: Tuesday 31-Jul-2007 10:15:54 AEST | No longer maintained. Pre-2018 was maintained and authorised by Grenville Armitage,