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What is the formula to subtract 2 value of -ve dB?

Question asked by ling on Apr 4, 2010
Latest reply on Apr 14, 2010 by Dr_joel
There is a Trace Functions in the Network Analyzer which allow us to display current measurement data, memory data and also some mathematic application of current linear measurement.

I am having problem on getting the formula for the subtraction of 2 –dB value. The formula below which I get from other website only applied to the +ve value.
For example, adding 2 levels 94+96+98:
L = 10log10(10^9.4+10^9.6  +10^9.8 ) =101.1

If I would like to have a subtraction on -22.699 and -22.406, I could not use the formula above. Anyone know how the subtraction being done on –ve value?  

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