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My question is simple. I know that the FCC regulates RF output at the IR (intentional radiator) but do they also regulate the EIRP output, and if so, with what device is this measured with?

Indirectly, they do. They specify IR output power and then qualify the antenna gain that may be used along with the IR. I wouldn't really expect them to come around measuring EIRP with a spectrum analyzer. When enforcement is an issue, I suspect that the burden of proof would be on the operator to demonstrate compliance, based on mfg. specs and other documentation showing loss/gain. Perhaps I am wrong.

http://ecfr.gpoaccess.gov/cgi/t/text/text-idx?c=ecfr&sid=69a96955263d1e3955820446af9100ff&rgn=div5&view=text&node=47:1.0.1.1.14&idno=47#47:1.0.1.1.14.3.242.31

Many thanks.

The FCC does specify max EIRP. I don't have the different 5 GHz bands memorized but I do in 2.4 GHz. 2.4 GHz is 36 dBm (4 Watts) for point to multi-point. In point to point, you can actually go over 36 dBm using the 3:1 rule. The 3:1 rule works as follows: Starting at 30 dBm of IR and 6 dBi of antenna gain, you must reduce the IR by 1 dB for every 3 dBi gain you get on the antenna. So, a simple chart would look like this.

IR......|.....Antenna Gain....|...EIRP

30....................6.....................36
29....................9.....................38
28...................12....................40
27...................15....................42
26...................18....................44
25...................21....................46

With that last calculation you are pushing 40 Watts of power... legally!

GT

Mario,

In answer to part of your original question, the FCC uses spectrum analysers and RF power meters, etc. All the testing is done inside full or semi-anechoic RF chambers.

They also put the WLAN device into a particular test mode. Consumers can't get to these test modes, as they usually involve special firmware, or at least special hooks to enable them.

The IEEE, on the other hand, has other methods that are defined in the 802.11 spec for measuring power. These are the numbers advertised by manufacturers, and can be used for comparing output power between units. The Japanese are big on comparing Occupied Band Width (OBW).

If everything is done right, you will meet both specs. Note that violating the FCC limits are the ones that will get you into legal trouble. They are especially keen on the high and low band edges where you could run into other (eg non-WLAN) devices.

The problem with relying on a manufacturers claims, is that some or all of their (power and sensitivity) claims may be suspect. For example, how many manufacturers quote their numbers by channel? The answer is not very many. In addition, transmit signal quality is also very important, but few advertise it and may not measure it correctly if they do. The IEEE has their own spec for measuring 802.11b EVM, and some manufacturers use a more traditional, and incorrect, RMS measurement. Yeah both are measurements, but designing to the IEEE spec is a more demanding task, and makes for better radios and cleaner signals.

Several companies make equipment that will take all these measurements. I prefer the Anritsu MT8860x's.