On 22 Jan 2007 12:14:21 -0800, miso@sushi.com wrote:

>I don't know if there are RF spectrum
>analyzers with such intelligence, but I don't see why not.

There are plenty that have enough intelligence to grind out true
power. I can't afford any of these. I can't even afford one with
obsolete IEEE488 bus.

>In datacom (again, back to voice band communications), some modems used
>guard tones to indicate the line contained data, not voice. The CCITT
>specification is based on energy, so making such measurements (energy
>in a bandwidth) is a desirable feature. That is, the tone had to be a
>certain value relative to the data energy, which was spread out.

Sorta. *ALL* modems 1200 baud and up include a scrambler. What the
scrambler does is evenly distribute the energy across the entire
bandwidth, thus reducing the peak power, and thus making it easier to
transmit. The required dynamic range is also reduced. OFDM and DMT
DSL modems do the same thing by splitting the data up into many
discrete carriers. The total energy in the bandpass is the same
whether scrambled or de-scrambled, but the peak power is quite
different.

However, this has nothing to do with what I was mumbling about. I was
questioning the original comment that one could just read the tx power
from a spectrum analyzer. With spread spectrum, it's not that easy.

--
# Jeff Liebermann 150 Felker St #D Santa Cruz CA 95060
# 831-336-2558 jeffl@comix.santa-cruz.ca.us
# http://802.11junk.com jeffl@cruzio.com
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