Radio Path v2.0					www.gbppr.org
---------------                                 -------------

A Perl script to graphically show the radio path profile between two points.  
It will plot the 0.6 Fresnel zone and the true radio path for a given
value of K (the effective Earth radius factor).  This is all displayed in
reference to the path's elevation data taken at intervals along the link
path.  You can also place obstructions or trees along the way to let you know
if you actually have a clear radio line-of-sight path.

Still (somewhat) experimental.



Needed programs
---------------

* Perl
* GNUplot
* GhostView



Quick start using the example data
----------------------------------

0.)  Type: ./radio_path.pl

1.)  For the operating frequency enter : 2.4

2.)  For latitude of Site A enter : 44.5292

3.)  For longitude of Site A enter : -88.04036

4.)  For latitude of Site B enter : 44.50858 

5.)  For longitude of Site B enter : -88.03237

6.)  For path step size distance enter : 0.25

7.)  For the effective Earth radius factor enter : 1.33

8.)  For the Nth Fresnel zone enter : 2

9.)  For Site A antenna height enter : 25

A.)  For Site B antenna height enter : 50

B.)  Wait a second...

C.)  GhostView should pop up showing your radio path profile.

D.)  The default output is a PostScript file named 'output.ps'.

E.)  The default Fresnel output is a file named 'output1.ps'.



Using your own data
-------------------

To use your own data, you'll first need to *hand* edit the 'Elevation' 
file.  Yeah, I know, it sucks.  Oh well.

Example Elevation file
~~~~~~~~~~~~~~~~~~~~~~

# Path step (miles)   Ground elevation (feet)   Obstruction height (feet)

0 (must be zero!)     590                        0 (at Site A)
0.25                  590                       30 (tree)
0.50                  590                       20 (small house)
0.75                  600                       25 (tree)
1                     590                       20 (tree)
1.25                  600                        0 (open field)
1.50                  600                        0 (at Site B)


You'll want to break the total path distance up into steps, say 1/4 mile, and
find the ground elevation and obstruction height at that specific location.

Do this for each point along your radio path, starting with zero, the first
antenna site (Site A).  End with the total path distance, say 1.5 miles, and the
elevation data for the second antenna site (Site B).



K Factor
--------

The effective Earth radius, K, is 1.33 in temperate climates.  Under typical
conditions K will vary from 1.2 to 1.6 depending on location, weather, 
seasons and time-of-day.

Typical Values of K
~~~~~~~~~~~~~~~~~~~
                                        Summer  Winter
Dry mountains (above 1500 meters)       1.20    1.20
Mountains (to 1500 meters)              1.25    1.25
Midwest and Northeast                   1.50    1.30
South and West Coast                    1.55    1.35
Southern Coast                          1.60    1.50



Nth Fresnel Zone
----------------

From SoftWright:

Even Fresnel Zone Reflection Points
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Another important use of Fresnel zone information is to check paths
(particularly microwave paths) for possible reflection points. The Fresnel 
zone formula shown above is the set of points where the distance from the 
transmitter to the Fresnel zone, then to the receiver, is longer than the 
direct path from the transmitter to the receiver.  For even numbered Fresnel
zones (N=2, 4, etc.), the difference between the direct path and the indirect 
path defined by the Fresnel zone distance, is a multiple of one-half wavelength.
If the geometry of the path is such that an even numbered Fresnel zone happens 
to be tangential to a good reflecting surface (a lake, a highway, a smooth 
desert area, depending on what wavelength is involved), signal cancellation 
will occur due to interference between the direct and indirect (reflected) 
signal paths.

You can set the Fresnel zone to even numbered values when plotting a profile 
to see if any potential areas of destructive signal reflection are present on 
the path.



Notes
-----

* Smaller step sizes for the elevation data are better.

* Elevation step sizes don't have to be equal.

* Use high quality, 7.5-minute topo maps or DEM data to get your elevation data.

* You could even use a GPS receiver and walk along the path plotting points.

* Text based 0.6 Fresnel clearance data is in the file '0.6_Fresnel_Step'.

* Refer to http://www.gbonline.com/~multiplx/wireless/page06.html for 
  more information on Fresnel zone obstructions.

* Refer to http://www.gbonline.com/~multiplx/wireless/environmental.main.cgi
  for a interactive environmental factor calculator.  This will allow you
  to accurately predict the K factor.

