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Safety and Power Emissions

What's safe and what's not? If your question is not here, try looking through all of the questions which are listed on TheEvolvingFAQ.

I fell off the roof of my home after installing an antenna, and I need someone to sue. Who runs this group, and who insures it?

We are (almost certainly) not liable, but if you feel we are contact the Committee.


Is 2.4Ghz radiation safe? I've heard it uses the same radiation as my microwave oven? Are you killing me and my chances to reproduce?


2.4Ghz signals used for 802.11b/g are limited by law to a maximum total output of 4W EIRP this is far lower then a microwave oven by over three orders of magnitude. Even high output cards only put out 200mw (milli-watts) of power, and thus need an antenna to hit the legal limit.

The WirelessHealth page is a collection of links aimed at promoting a better understanding of Radio Frequency Electro Magnetic Radiation (RF and EMR) and the known health risks.


Someone mentioned 4w is the max power output allowed. I want \"more power\" and I'm willing to spend some serious money to boost my signal (and to microwave my neighbours, the people who live in a 10km radius and the surrounding wildlife).

You will be breaking Australian comunications law and will be liable for a very large fine.
We have links over 50KM that are legal, and we can say from experience that latency at distances above 50km causes serious problems. Even if you could push the radio signal for 500KM, the link would be unusable.


How do I do this? Whats the deal with EIRP?

Well, EIRP stands for Emission of Isotropic Radiated Power. The limit for 802.11b compliance in America, and also in Australia, is 4W EIRP. In terms of signal output power, that's 36dBm.

The output power for a Lucent/Orinoco/Agere/Avaya 802.11b PC card is 15 dBm. If there is no external antenna then that's the answer. 15dbm. This is also labelled as 30mw power output. There are some devices with 100mw and 200mw output, but there is no benefit to performance unless youre trying to achieve massive distances in a crowded area with poor antennae.

If you're trying to overcome a problem with a long-distance link, first get bigger antennae, check the link for obstructions and faults with equipment, experiment with warping space/time, or move to a different radio spectrum/channel, before you think about upgrading to a more powerful device.

If you attach a 2.4ghz amplifier, you need to be careful that the rated output power does not go over the 36dBm limit once you attach an antenna and a low-loss cable to the amplifier. See the next question for details on how to check this.

'NB' adding an amplifier to an 802.11b card will almost certainly be illegal, as it contravenes the class license on the device.


How do I work out my EIRP then?


Example: we have a PC Card with a 14 dBi external antenna (a modded galaxy antenna) and 50 ft (12.7 Metres) of LMR400. we make the assumptions that the total loss for a pigtail adapter is 0.5 dB and the loss for each connector on LMR400 is 0.5 dB.

using a quick formula, here's how we work out the EIRP:

PC card - pigtail adapter - connector - 50 ft (12m) of LMR400 - connector + 14 dBi antenna = ? dB of Total output power

15 dBm - 0.5 dB - 0.5dB - 3.3 dB - 0.5 dB + 14 dBi = 24.7 dBm

The maximum is 36dBm, which makes 4W EIRP.

the resulting signal is roughly 10x stronger than what comes out of the wireless card, and within the safe limits of the EIRP restriction, which is 120x the output power of the card.

For more information on working with decibels (dB), and some lookup tables, check out PowerAndGainToDecibels



Can't find the answers to your questions?
Try looking through all of the questions listed on TheEvolvingFAQ. If you still can't find answers, ask your questions here.


Version 10 (current) modified Tue, 03 Jul 2007 23:12:20 +1000 by tyson
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