Why is there a difference in the variation of the same graph in Frequency/Time graphs?

Discussion and questions regarding the Radiated Immunity and Conducted Immunity modules of RadiMation.
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incognito
Posts: 235
Joined: 03 Feb 2012, 13:07

Why is there a difference in the variation of the same graph in Frequency/Time graphs?

Post by incognito »

I'm using the Multiband radiated immunity test to perform a test.
Graphs for the 'Electrical Field Substitution method' are available in the graph on the 'Frequency' tab, and also as a graph in the 'Time' Graph.

See the screenshot:
FrequencyTimeGraph.png
FrequencyTimeGraph.png (220.5 KiB) Viewed 2614 times
There is however a difference between the graph in the 'Time' graph compared to the graph in the 'Frequency' graph.
The graph of the 'Electrical Field Substitution method' varies with roughly +- 2 V/m in the time graph, while the same graph varies with less than 1 V/m in the frequency graph.

Why is there a difference in the variation of the graphs?
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joro
Posts: 440
Joined: 24 Aug 2011, 09:55
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Re: Why is there a difference in the variation of the same graph in Frequency/Time graphs?

Post by joro »

It is indeed correct that there could be a difference in the variation in the graph of the same value between the time graph and the frequency graph.

The frequency graph shows the value, based on a frequency index. For every unique frequency there is thus only a single value shown. The value that is shown for each frequency, is the value that is present at the moment that the dwell-time is active. For EMC immunity testing, the value at the moment that the dwell time is active is the value that should be reported.

The time graph shows the value, based on a time index. For every unique time there thus only a single value shown, however as time is running fast, there can be several values within the same second, that are all measured on an unique sub-second time index. The Time graph thus shows all the values that are measured, as they are all measured on their own unique time moment. For a single unique tested frequency, it is thus possible that multiple values (on different times, but on the same frequency) are measured. This for example happens when the power is being regulated to the correct testlevel. As the time graph is showing all the values, it is possible that there is a greater variation in the time graph then there is on the frequency graph.

To conclude: The frequency graph only shows the value as it is measured during the dwelltime. The time graph shows all the measured values also those values that are measured during the power regulation, which are values that are measured outside of the dwelltime period.

If for example a frequency change mode with a 30 dB ramp down is configured, then the time graph of the signal power graph, will show the individual steps during the ramp, and thus will show a 30 dB variation. In the same test, the signal power graph in the frequency graph, will only show the signal power during the dwell time, which is the top of the ramp.
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