[BAWUG] dBM and dBi
Tim Pozar pozar@lns.com
Thu Mar 7 15:39:00 2002
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On Thu, Mar 07, 2002 at 06:06:59PM -0500, Stefan Schueller wrote:
> How do I convert dBM to dBi or watt and what is the legal limit? 36dBi or
> dBM?
Both answers can be found from my paper "Demystifying the FCC's
Part 15 Rules and Regulations on ISM power limits" at:
http://www.lns.com/papers/part15/
--
At the end of the paper...
--
1.deciBels - dB
dB, or one tenth of a Bel, is a unit of mesurment that looks
at the ratio of one value to another. Gain or loss can be
measured in dB. The dB scale is an exponential scale using
the formula log(ratio)*10. This means that 3 dB is about
twice the power, 10 dB is 10 times the power, 13 dB is about
20 times the power and 20 dB is 100 times the power.
2.dBm
dBm is deciBels referenced to a value of 1 miliWatt of
power. Power over or under 1mW would be plus or minus dBm
respectively. If you have a transmitter that produces 1
watt of power that would be 1000 times more than 1 mW so
that converts to 30 dBm.
3.dBW
dBW is deciBels referenced to a value of 1 Watt of power.
Power over or under 1 Watt would be plus or minus dBW
respectively.
4.Effective Isotropic Radiated Power - EIRP
Effective Isotropic Radiated Power defines the gain of an
antenna over an "isotropic antenna" that would radiate
equally in all directions.
If you have an antenna that radiates better in one direction
than another, it would have gain in this direction. The
amount of gain would be shown as "dBi" or dB gain (or loss)
over an "isotropic antenna".
--
Snail: Tim Pozar / LNS / 1978 45th Ave / San Francisco CA 94116 / USA
POTS: +1 415 665 3790 Radio: KC6GNJ / KAE6247
"It's a damn poor mind that can only think of one way to spell a word."
- Andrew Jackson
"What is wanted is not the will to believe, but the will to find out,
which is the exact opposite." - Bertrand Russell, "Skeptical_Essays"
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