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From: Grant Taylor <gtaylor@tnetconsulting.net>
Newsgroups: sci.electronics.design
Subject: Re: dBs
Date: Sun, 26 May 2024 14:05:43 -0500
Organization: TNet Consulting
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On 5/26/24 12:58, Cursitor Doom wrote:
> I was under the impression that one couldn't simply just add dBs to dBms?

I've had very similar question in the laser power on fiber and was given 
the following understanding:

dB is simply a ratio while
dBm is a ratio referenced against a known thing.

dBm is anchored while dB is floating.

It's sort of like saying someone raised the picture four feet (dB) after 
the picture started two feet off the ground (dBm).

It's been years since I had it explained to me and I may be wrong and / 
or the context it was explained to me is different than the context you 
are asking in.

N.B. the measured aspect of dBm is somewhat of a nomenclature but I 
believe the m references 1 mW of power.

Then there's the logarithmic aspect and decimal aspect making dB / dBm 
somewhat more unintuitive to me.



-- 
Grant. . . .