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| reply to grohgreg
Re: Minimum cable length said by grohgreg :
When an unqualified "dB" is used, it's usually assumed dBW.
I'm sorry, I'll have to disagree with you here. In 25 years of satellite engineering, I've never seen this assumption. If it's "dB", then it's either gain/loss, or a ratio (like C/N). Otherwise, a 10 dB attenuator would reduce the signal by 10 Watts, which doesn't make sense... I would be interested if you could point me to an example of this usage. And I certanly know the difference between dBm and dBW (it's 30 dB  )
said by grohgreg :
Nor do you seem to have a real good handle on the difference between voltage and current.
I've got a very clear handle on this; though I did blur the destinction in my response. Sorry for that.
The key is that the voltage is not used to control the TRIA in any way. | |
 grohgregDunno. Ask The Chief
join:2001-07-05
Dawson Springs, KY | 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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| 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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