bi241@scn.org hath wroth:

>easy mate, interpreting the FCC, the IRS and the US Constitution
>shouldn't be that difficult

True. It shouldn't, but it is. I've been dealing with the FCC on and
off since about 1968. These days, rules-n-regs are scribbled by
attorneys, not engineers. I'll spare you my list of horror stories
over the years.

>you see, a standard industrial spectrum analyzer, with proper input
>attennuator settings, hooked up directly to the RF transmitter at the
>connector will show exactly the TX power of the device. Simple as that!

Nope. Quiz time:

You have a spectrum analyzer that shows an 802.11g spread spectrum
signal that is approximately 25Mhz wide. Peak power on the scale is
0dBm to make the calculations easy. The spectrum analyzer IF
bandwidth is 500KHz. What is the "real" power (ignoring duty cycle)?

I'll supply the answer tomorrow. Note that this is not a trick
question and the numbers are quite real.

>now, suppose the measure of TX power is at the transmitting antenna,
>then of course there's another setup and calculation for the spectrum
>analyzer to do just that, but it begs the questions

What question? The FCC is usually very clear where to measure things.
They missed this time. However, I've learned from bitter experience
to NEVER ask the FCC for clarification, because I've always gotten the
answer I least expect, and often with unpredictable side effects.

>1) how far away from the transmitter should the spectrum analyzer be
>positioned? 0 feet? 1 feet? 3 feet? 10 feet? 10 miles?

You're measuring power output, not field strength. If you want to
measure RF field strength, there are some rather simple guidelines
intended to keep your spectrum analyzer out of the near field and only
pickup the far field. The only time the distance needs to be
specified for the test is when measuring incidentally radiation. For
field strength, anything resembling a calibrated antenna will work to
calculate the field strength.

>2) what is the standard for the field-probing antenna? loop? yagi?
>omni? what about its sensitivity?

The type certification, they're rather specific in what may be used.
Go to the FCC ID web pile and pick any likely FCC ID number for a
wireless device. The applicants are required to supply photographs of
their test setup, which includes the test antennas.

>3) if the probing antenna is to be right at the transmitting antenna,

It's not.

>then what part of the transmitting antenna should it touches? the head?
>the tail? the middle? the center? the rim? at what angle?

None. Look at the photos on the FCC ID web pile. They have to be far
enough from the unit under test to not be considered within the near
field.

>sounds like the things only a clown would do in a circus, eh?

Ummm.... I'm one of those clown. Thanks for sharing. Bye.

>oh and why not buy at Fry's?..... like, the things you buy from the
>store would fry themselves... or what?
>just kidding
--
Jeff Liebermann jeffl@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