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I recently ran across some WIFI adapters on Amazon that claim to have 2000mW of power. However, to the best of my research, there is an FCC limit of 1000mW on omnidirectional antennas. Are these devices only for use outside the USA?

Edit: I understand most people here are not lawyers so I probably shouldn't have asked for exact legal advice. Rnxrx has however provided some very useful information regarding how wifi signals are measured which should be useful outside of legal and locality spaces. I suppose the question would be better geared towards how the power advertised by a manufacturer can differ from the radio transmitter's actual power.

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Please read the FAQ. Not only is this too localised but it has absolutely nothing to do with system administration. If you want to find out whether or not something is legal in your particular spot on the planet get proper legal advise. –  John Gardeniers Jun 15 '12 at 0:45
    
@JohnGardeniers, I did, the FAQ specifically mentions "Network routing, switches, and firewalls", I would think Wifi would fall in that category. If the whole USA is too localized, I apologize for my question. –  XHR Jun 15 '12 at 0:54
    
@XHR - "localised" is very very broad. If it's only applicable in one country, no matter how big the country is, or if the country is at the center of the universe, too bad. Additionally, we can't answer this because we're not lawyers. –  Mark Henderson Jun 15 '12 at 1:01
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So if someone asks for technical advice about a problem with a T1 is it still too localized because it's a standard essentially limited to North America? How about SONET vs SDH? UPS designs for different frequencies and voltages? The question asked isn't inherently solely a regulatory question (i.e. how do I comply with x electrical code) but rather speaks to a more fundamental question of how network design in wireless networks is accomplished by IT professionals. –  rnxrx Jun 15 '12 at 1:10
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OK - then it follows that questions about how best to accomplish terminating WAN services from the UK to terminate in Australia should be shut down as well? Actual useful and practical network questions may have to deal with the realities of how to design / acquire / terminate services in many (localized) places. –  rnxrx Jun 15 '12 at 13:19
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closed as off topic by Zypher Jun 15 '12 at 21:15

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2 Answers

up vote 5 down vote accepted

1W is the limit at the transmitter, but higher EIRP amounts are allowed for certain kinds of antennae. A 6 dBi multipoint antenna connected to a 30dBm (1W) source yields 4W EIRP - which is within the legal limit. Much higher limits are specified for point-to-point setups. The question isn't so much the claim of 2W but rather where- and how- that 2W is measured.

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A "5dbi" antenna is probably exactly NOT omnidirectional.

http://www.squidoo.com/are-super-long-range-wifi-antennas-legal-

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cisco.com/en/US/docs/wireless/antenna/installation/guide/… - 5dBi Omnidirectional antenna –  rnxrx Jun 15 '12 at 0:33
    
If an antenna has gain, it is not omnidirectional unless it incorporates an active amplifier, which would be equivalent to driving an omnidirectional antenna from a transmitter above legal power. Except if the amplifier only provides RX gain, which would probably worsen your problem by making your reach asymmetric even if it had a low enough noise figure not to worsen the problem anyway. The description "omnidirectional" in the marketing literature probably means "prefers sideways transmission to earth- and skywards", which is not omnidirectional in a radio technical sense. –  rackandboneman Jun 15 '12 at 0:51
    
Huh? Maybe I'm missing something but there are literally hundreds of omnidirectional antennae on the market, virtually all of which are completely passive. In the more general sense there are also definitions of omnidirectionality (en.wikipedia.org/wiki/Omnidirectional_antenna) that also seem to refute the above. Apologies if I'm missing something obvious. –  rnxrx Jun 15 '12 at 1:00
    
Hmm then the question is whether the FCC limit is really on omnidirectional or on isotropic.. I might indeed have mixed up the two, but radio power limits usually apply to isotropic antennas... –  rackandboneman Jun 15 '12 at 9:19
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-1 Omnidirection broadcast on a 2D plane (or try, hence the gain). Isotropic "antenna" would broadcast in every direction (semi-equally) and have no appreciable gain. Also, please do not post just a link, especially to a transient site like squidoo. At least transcribe the important parts of the page so we have them should the linked site no longer be available. –  Chris S Jun 15 '12 at 13:46
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