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Keysight Instrument Rack E7950A-1.3m E3661B-1.6m E3662B-2.0
Set Up
6.51 dB = x/10 dB Now solve for x:
x = 65.1 dB
Thus, adding 50 dB to 65 dB results in a 0.1 dB increase in noise.
Example 2. What is the maximum estimated noise level of a product I want to
install if the system is currently rated at 65 dB and my limit is 70 dB?
Original equation with variable x. x dB = 70 dB – 65 dB
Divide by 10.
x/10 dB = 70/10 dB – 65/10 dB x/10 dB = 7.0 dB –6.5 dB
x/10 dB = 0.5 dB
Write the equation in powers of 10 (dB units are Log base 10 units). 10
x/10
= 10
0.5
Take the log of both sides of the equation (return to dB units). x/10 dB = log(0.5)
= 6.837 dB
Solve for x. x = 68.37 dB
More than double the noise is required to increase the total noise from 65 dB to
70 dB.
Estimating Total Noise
For a quick estimate of total noise from two sources, see Figure 13 if the two dB
levels are within 16 dB of each other. If the difference is greater than 16 dB, the
effect of the lower noise level is negligible (zero for calculations).
Figure 13
Estimating System Noise
For example, the combination of a 50 dB noise and a 54 dB noise has a
difference of 4 dB. Using Figure 13, 4 dB difference results in adding 1.4 dB to
the higher noise, resulting in an estimated 55.4 dB total noise.