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RF Components: Tailored ENR Values

Tailored ENR Values

Broadband Coaxial Noise Sources, with tailored ENR
The optimum ENR of the noise source is dependent on the expected noise figure of the DUT. If the expected noise figure is high, the measured difference of the off and on noise source states will be too hard to discern accurately with the DUT's comparatively large amount of self generated thermal noise. However if the expected noise figure is very low than using a noise source with too high a level of ENR will cause the two measured values to have such disparate amplitudes that non-linear dynamic range issues may compromise accuracy. Depending on how crucial the measurement uncertainty window needs to be, the designer can mathematically calculate the theoretical best ENR. This process can be exhaustive mathematically. Table below indicates a quick rule of thumb for ENR vs. expected noise figure. It should be noted that any path loss between the noise source and DUT must be accounted for. If a 10 dB noise source makes sense for the DUT but there is a 10 dB coupler and 3 dB of insertion loss, than a noise source with a 20 - 25 dB ENR is needed.
Expected Noise Figure Noise Source Nominal ENR
0 to 10 dB 5 dB
10 to 20 dB 10 dB
20 to 35 dB 15 dB

High ENR Noise Sources are perfect for built-in-test situations where there is significant path loss between the output of the noise source and the receiver.
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