Basic wireless info: FHSS

Keep in mind these can be plus or minus 20db, given conditions, but here's some good basic quick estimate numbers.

From: Kent Britain [mailto:WA5VJB@FLASH.NET]
Sent: Wednesday, October 15, 2003 8:45 PM
Subject: Steve, I'll let you pass this along to the group

It has been asked that we pass along our testing methods and
performance predictions for 2.4 GHz Products.   RDI, and it's
spin off companies Corecam and Xanboo make about 10,000 TV
cameras a month, most of which are wireless.  Power levels and
bandwidths are similar to many wireless products.
We also make wireless home security systems and do contract
manufacturing of many wireless products.
I recognize and least one of our customers in this working group.

2.4 GHz Path loss

feet        dB
2000        96
1000        90
 500        84
 400        82
 300        79
 200        76
 100        70
  75        67
  50        64

Our measurements show an average 4 dB loss for an interior wall.
Wood 2x4 or Metal equivalents didn't change this number.

For Exterior walls we've measured an average 14 dB loss.
Again construction of the wall made little difference.
Using a high gain NARDA horn antenna, I effectively
imaged the walls.  This showed that the majority of the signal
was refracting off the top edge of the wall, not actually passing
through them.
Sometimes the windows were a hot spot depending on
the construction of the window, reflecting film, metalization,
and fiberglas vs wire screens.

We take a set of video units out on the antenna range, or the
road in front of the lab and measure their typical range.
The road or test range needs to be fairly flat, the surface has
little effect.  Dirt, Grass, concrete, asphalt, etc. are all well
beyond Brewester's angle after 50 ft or so.  Thus the surface
appears reflective.  Moisture content would vary the Brewester's
angle point slightly, but would not change far field levels.

Example 1
Video unit goes 400 ft and the customer wants to run
the signal through an exterior wall.
82 dB - 14 dB = 68 dB
68 dB is about 80 ft for the expected range.

The Video unit again goes 400 ft and the signal
will pass though 2 interior walls.
82 dB - 8 dB = 74 dB
74 dB is a bit over 150 ft expected range.
Advertising dept uses the 400 ft of course, but these
are the typical range examples we put in our consumer

Example 3
Imagine you are standing along the shore of a
clear mountain lake.  The air and water are
perfectly still.
You look down are your feet and see the little
minnows swimming around.
You look out across the lake and see the pines
mirrored on the water.
WAIT, is water transparent or Reflective???
That point about 50 ft away where the water
turns reflective is Brewester's Angle for water.
Same holds true for Concrete, Asphalt, etc at
2.4 GHz.

When I get a little time, I'll explain how we
deal with multi-path.

Kent Britain
Sr RF and Compliance Engineer