Power Levels and Amount of Radiation
fake....@stonyx.com
is bad for you or not, and without metioning the fact that we're
exposed to it from a lot of other sources .... I was wondering if
someone could help me with a quick question.
Wireless routers and cards seem to mention two items when it comes to
their signal power levels. The signal power in dBm (usually around
15dBm) and an antenna measurement in dBi (around 5-10dBi). My question
is, if two different routers both mention 15dBm as their transmitting
power, but one has a 5dBi anetanna, the other a 10dBi antenna, are they
producing the same strength/amount of radiation or is the one with the
10dBi antenna producing twice the strength/amount of radiation?
Thanks,
Harry
Jeff Liebermann
>Without getting into any debates about wether electromagnetic radiation
>is bad for you or not, and without metioning the fact that we're
>exposed to it from a lot of other sources .... I was wondering if
>someone could help me with a quick question.
Sigh. You're no fun...
>Wireless routers and cards seem to mention two items when it comes to
>their signal power levels. The signal power in dBm (usually around
>15dBm) and an antenna measurement in dBi (around 5-10dBi). My question
>is, if two different routers both mention 15dBm as their transmitting
>power, but one has a 5dBi anetanna, the other a 10dBi antenna, are they
>producing the same strength/amount of radiation or is the one with the
>10dBi antenna producing twice the strength/amount of radiation?
It's the sum of the power output and antenna gains (in decibels).
In your example, the router 1 radiates:
+15dBm + 5dBi gain = +20dBm
while router 2 radiates:
+15dBm + 10dBi gain = +25dBm
The radiated power is 5dB more for router 2 than router 1.
However, that doesn't directly give you field strength and exposure.
Field strength is in milliwatts per square centimeter, while exposure
is a complex mess involving SAR (specific absorption rate) which
include frequency and near-far field effects.
Simple calculator:
| http://n5xu.ae.utexas.edu/rfsafety/
FCC exposure guilelines:
| http://www.fcc.gov/Bureaus/Engineering_Technology/Documents/bulletins/oet65/oet65.pdf
Broadcast Suppliment:
| http://www.fcc.gov/Bureaus/Engineering_Technology/Documents/bulletins/oet65/oet65a.pdf
Ham Radio Suppliment:
| http://www.fcc.gov/Bureaus/Engineering_Technology/Documents/bulletins/oet65/oet65b.pdf
Cellular Suppliment:
| http://www.fcc.gov/Bureaus/Engineering_Technology/Documents/bulletins/oet65/oet65c.pdf
--
Jeff Liebermann je...@comix.santa-cruz.ca.us
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558
Moe Trin
<1145760553....@z34g2000cwc.googlegroups.com>,
fake....@stonyx.com wrote:
>Without getting into any debates about wether electromagnetic radiation
>is bad for you or not, and without metioning the fact that we're
>exposed to it from a lot of other sources .... I was wondering
I'll agree with Jeff - you're no fun
>Wireless routers and cards seem to mention two items when it comes to
>their signal power levels. The signal power in dBm (usually around
>15dBm)
Things to think about - that signal power in dBm (dB = deciBels - a ratio
and m = milliwatt - the reference level) can be likened to the size of
a light bulb - lets say 100 watts for hand waving.
>and an antenna measurement in dBi (around 5-10dBi).
the gain of the antenna measured in decibels referenced to an isotropic
radiator. That light bulb is more or less an isotropic radiator, as it
radiates (more or less) equally in all directions. Now, antenna gain
is obtained in a similar mode to those lightbulbs, using reflectors and
lenses - to _concentrate_ the radiation in a desired direction. Think
of the difference between a bare incandescent lamp and a flood light and
a spot light - all with (example) 100 watts. Which one is brighter?
Well, the spot is going to be brighter in one direction compared to
the flood or bare bulb, but the bare bulb will light up in all directions
not just one.
>My question is, if two different routers both mention 15dBm as their
>transmitting power, but one has a 5dBi anetanna, the other a 10dBi antenna,
>are they producing the same strength/amount of radiation or is the one with
>the 10dBi antenna producing twice the strength/amount of radiation?
That depends on how are you measuring the power. If you sum up all of
the power radiated in all the directions because you are four inches
from the antenna, then both may be more or less equal. If you are looking
at the peak power in the ideal direction, then the 10 dBi antenna is
producing 5 dB (or 3.16 times - decibels are logarithmic) more signal
strength. And if you are not in the direct line of fire (think about
that spot light again), then "it depends".
Then, as Jeff notes, there are all kinds of other dependencies. Bottom
line - there is no simple answer without making some assumptions.
Old guy