[993] in resnet
Re: 802.11b signal ranges
daemon@ATHENA.MIT.EDU (Jim Warner)
Sat Mar 16 11:41:36 2002
Message-ID: <200203161641.IAA21799@sasha.UCSC.EDU>
Date: Sat, 16 Mar 2002 08:41:58 -0800
Reply-To: Resnet Forum <RESNET-L@listserv.nd.edu>
From: Jim Warner <warner@CATS.UCSC.EDU>
To: RESNET-L@listserv.nd.edu
> I keep seeing 15dBm is that the same as 15mW?
No. 0 dBm is 1 milliWatt.
To figure the power, divide dBm by 10. Raise 10 to
that power. Multiply by 1 mW. So:
0 dBm = 1 mW
10 dBm = 10 mW
15 dBm = 30 mW
20 dBm = 100 mW
My understanding is that the effective radiated power
in the 2.4 GHz band must be below 1 Watt in the U.S.
The limit is on the product of the power and the antenna
gain. The rules say that it is the manufacturer's
responsibility to make sure that users can't hook high gain
antennas up to their radios and achieve a greater-than-legal
power -- hence the hard to find and confusing array of
antenna connectors that appear to be designed to thwart
interchangability.
Power limits in some other countries are different.
If you get equipment that was intended for use in a
low power country, something will have been done to
reduce it's output power. Typically what is done is
an internal firmware setting. While it might be possible
to reprogram a radio to a different country's power limit,
that would likely be illegal.
Note that even if someone made a 1 watt transmitter in a
PCMCIA package, it's effect on you laptop's battery life
would not make you happy. And it would likely generate
more heat than the PCMCIA package could handle.
-jim warner
UC Santa Cruz
___________________________________________________
You are subscribed to the ResNet-L mailing list.
To subscribe, unsubscribe or search the archives,
go to http://LISTSERV.ND.EDU/archives/resnet-l.html
___________________________________________________
