[Amps] Measuring RF Power

[Harold B. Mandel]

Dear Gary,

You're acquainted with 3-phase electricity, yes?

Imagine looking down the edge of the wire and seeing 
waveforms, infinitely thin, popping out at 0, 120 and 270
degrees. Kind of vector-ish, not really quantifiable, just 
an image.

In cellular radio, look down that same wire and see
128 waves popping in and out, but this time, they 
wobble, sometimes at their peaks, sometimes while
going up or coming back down.

The NTSC television system has a "vectorscope" 
for lining up the correct color bursts when setting up
a multi-camera shoot, so that everybody's Cyan, etc.
is Cyan, etc. It's kind of the same picture: rotational angles,
magnitudes.

In GSM cellular radio, the display that's supposed to be
"textbook" looks like my three year old grandson was
given a pencil and told to scribble inside a circle. 

However, each of the vectors is precise, and what makes
us field people crazy is that a 5% phase angle error, 
(that CAN be caused by a poor coaxial fitting), can lead to
a 10% desensitization of the corresponding receive channel.

The Agilent power meters are now a steal at $14 thousand
apiece. They're five across, three up and about ten down,
and have all sorts of internal software to come up with 
an "average" power display.  I saw one technician use a 
Bird 43 and measure 22dB, then use an Agilent and came up
with 68dB. Needless to say, all Bird 43's are toast in GSM.

Hal