|reply to american express |
Re: [general] dBm vs. milliwatt confusion
If you have a 24 dBi gain antenna and you drive it with 24 dBm of transmit power and there are no losses in the system your EIRP will be 48 dB EIRP.
Since 36 dBm ~= 4 Watts
and since every three dB of gain equates to about twice as much power....
36 + 3 dBm ~= 8 Watts of ISOTROPICALLY RADIATED Power
39 + 3 dBm ~= 16 Watts of ISOTROPICALLY RADIATED Power
42 + 3 dBm ~= 32 Watts of ISOTROPICALLY RADIATED Power
45 + 3 dBm ~= 64 Watts of ISOTROPICALLY RADIATED Power
So NO your EIRP would be about 64 Watts rather than 10 Watts. What we need to understand here is that EIRP stands for Effective Isotropically Radiated Power or Equivalent Isotropically Radiated Power. It does not mean that you are actually transmitting that much power. It means that it LOOKS LIKE YOU ARE TRANSMITTING WITH THAT MUCH POWER BUT ONLY IN THE FAVORED DIRECTION.
The truly cool thing happening here which is so often overlooked it the idea that a good antenna can make a 250 mw transmitter LOOK LIKE a 64 Watt transmitter in the favored direction. That is a whale of a lot more interesting than power tweaks on custom Linksys firmware, don't you think?
The Sveasoft distribution model has been ruled compliant with the GPL by the FSF. Nobody else has a right or requirement to rule on it.
Santa Rosa, CA
The best analogy is a flashlight. A bare bulb (dipole antenna) radiates in all directions and lights up everything a little bit. But put that reflector on it and you can see many times further....but only within a small cone of light.
Putting a flat mirror behind a bare bulb would double the light in front of it (3dB). Putting it in within a parabolic reflector gives you a huge increase, but only in one very-narrow direction.