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grohgreg
Dunno. Ask The Chief

join:2001-07-05
Dawson Springs, KY

reply to joebob42

Re: Minimum cable length

said by joebob42 :

I would be interested if you could point me to an example of this usage.
No problem: see »www.atis.org/tg2k/_dbw.html. Note the definition; "dB referenced to one watt". So when you say "dB", I see an all-encompassing term. Generic, if you will. True, "dB" expresses a "ratio", but relative to what? It could be dBA, dBC, dBV, dBm, dBi, dB0, dBW et cetera.

To see what I'm talking about - the difference between a simple "dB", and the specific "dBm" - see »www.isa.org/Content/ContentGroup···_dBm.htm. dBm is specific to miliwatts. When you're talking negative power levels (-5 to -35 for example), it's absolutely imperative to keep the discussion in dBm.

//greg//
--
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joebob42

@66.36.x.x

said by grohgreg :
Note the definition; "dB referenced to one watt".
This is the definition for dBW. dB is always a ratio. Nothing here says that "dB" can be assumed to be dBW. If you're talking about the gain of a device, it's gain in dB is derived from the ratio of its output power to its input power, at its normal operating point.

Your second reference states quite clearly: Use dB when expressing the ratio between two power values. Use dBm when expressing an absolute value of power. My usage is consistant with that. So, I still don't see why you assume when I write dB, I really mean dBW.

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