Notes N9SSA's Miles Per Watt Calculator
Popularized by my friends at:
QST, January 2014 issue?
QRP Amateur Radio Club International
QST, June 2000 issue, Page 31
The Grid Locator and Field Hunting newsgroup
Enter the longitude and latitude of two points in the standard +-
format. For example: Chicago is Latitude: 41.880833, Longitude:
-87.62785. Optionally, you can enter the gridsquare (2, 4 or 6
characters) and the calculator will automatically convert to Latitude
Values for South and West are to be negative. Enter your power out in
watts, and press the button!
You may also click Yes to have the calculator remember your FROM qth for the next time you visit.
If you want to see a map of your two points, press the Show Map button.
You can get coordinates for any site on earth through maps.google.com
or coordinates of a callsign via BuckMaster.
These, and other useful links are in the Tools section of the
calculator. For ease of use with the calculator, I suggest you open
tools with a RIGHT mouse-click, and "Open in New window", that way you
can copy and paste back to the calculator window.
Notes on Great Circle Distances -
The problem of determining the great circle distance on a sphere has
been around for hundreds of years, as have both the Law of Cosines
solution (not recommended) and the Haversine Formula:
Haversine Formula (from R.W. Sinnott, "Virtues of the Haversine",
Sky and Telescope, vol. 68, no. 2, 1984, p. 159):
R = 6367000
dlon = lon2 - lon1
dlat = lat2 - lat1
a = (sin(dlat/2))^2 + cos(lat1) * cos(lat2) * (sin(dlon/2))^2
c = 2 * atan2( sqrt(a), sqrt(1-a) )
d = R * c
Where R is the radius of the earth. I used earthradius=6367000 meters. The earth
actually varies from 6336 km to 6399 km.
This will give mathematically and computationally exact results. The
intermediate result c is the great circle distance in radians. The
great circle distance d will be in meters.
I based my distance calculator on the above formula. While not exact, it should give
you results that will be within a couple of miles.
For further discussion, refer to http://www.movable-type.co.uk/scripts/gis-faq-5.1.html.
Notes on Gridsquare Conversion -This program will break
down a gridsquare entry and convert it to Latitude and Longtitude. You
can enter 2, 4 or 6 characters, and the calculator will select the
center point of the grid (two chars), subgrid (4 chars), or sub-sub
grid (6 characters).
Note that this program will takes lat/lon input literally. That is
52 degrees, 20 minutes is 52.3334. 52.3333 will resolve a different
gridsquare than 52.3334. (No biggie). To experment, try 52.3333lat by
5lon and 52.3334lat by 5lon. Note how they come up with J022mh and
For further information on this, check out:
In January of 2014 I rewrote the Mapping function to draw the signal path using a geodesic line utilizing Google Maps mapping API v3, based on the following code:
While the maps are nice, it may not reflect the actual path traveled by your signal. Holland, Michigan to Perth Australia, for example. Did your signal travel west? Maybe it went east!
Version History -
2.5 - Disabled broken Cookies. Added to To-do List!
2.4 - Fixed Mapping to draw using Google maps APIv3. Fixed broken links. Fixed cookies.
2.3 - Added Creative Commons license.
2.2 - Repaired mapgen.php
2.1 - Added Cookie to save home QTH location for repeat visitors
2.0 - Wrote companion program, mapgen.php, to display short path on Google Map with the
Google Maps EZ interface to
1.5 - Moved hosting from qsl.net to hoffswell.com
1.3 - Fixed remote broken links, including parc.xerox.com mapping
1.2 - Added input error checking, clean up code.
1.1 - Added tool bar. Added Lat/Long to gridsquare converstion.
1.0 - Original release, including gridsquare to lat/lon conversion, MPW calculation, and map button.
A special note of thanks...
Thanks to all my ham buddies that helped out with ideas, code, comments, suggestions and testing:
Darrell Kindred of Indio,
W2IOL, N0IT, WB0JNR, W8EL, N4EUK, W9IP, N1BWT and NT7S.
Please direct comments to firstname.lastname@example.org.
Last update 01.Jan.14
N9SSA MPW Calculator by Pete Hoffswell is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License.