Maidenhead Grid Squares

This script from the Houston AMSAT Net was written by AMSAT Area Coordinator Bruce Paige, KK5DO. Authorization is given for the use of this information over any ham band. Please give credit for the script where credit is due.

Tonights topic is Maidenhead Grid Squares, What they are and where do they come from.

Have you ever worked a satellite or sideband contact and the operator says "I'm in EL29hk"? I know where Houston is and I know where New York is. But where is EL29hk?

Where do those funny letter and number combinations come from? At a conference in Maidenhead, England in 1980, an international group decided this type of coordinate system would be used because the older QRA locator system could have a duplicate location outside Europe.

Maidenhead grid squares or simply grid squares represent a position on the earth based on latitude and longitude. The world is first divided into 324 large areas. These areas cover 10 degrees of latitude by 20 degrees of longitude and are called fields. Each field is divided into 100 squares. This is where the name grid squares come from. Each of these 100 squares represent 1 degree by 2 degrees. This gets us the EL29 which is what most people will exchange and also what is used for awards such as the VHF UHF Century Club award.

The two letters that follow a grid square further define your location within that square by dividing each square into a sub-square. These sub-squares are 5 minutes by 2.5 minutes. If I remember my high school math, 1 minute of latitude is equal to 1 nautical mile. It is more difficult to calculate longitude, since 1 minute of longitude at the equator is equal to 1 nautical mile it decreases as it goes towards the poles. Therefore, each sub square, such as EL29hk is equal to 5 nautical miles by 2.5 nautical miles. And, the grid square, EL29 is equal to roughly 120 nautical miles by 60 nautical miles.

So as you can see, one grid square covers a large area. In fact, you will almost find everyone in New Jersey that you work is in FN20. It seems that is one of the most densely populated areas of the country for Hams that operate satellite.

So, now that you know where these numbers come from, how do you find out what yours is? I live about 2 miles from an airport. I called the FAA and asked them for the latitude, longitude and elevation of the airport. They looked it up in a book and gave me those numbers. Then, I loaded the values into my InstantTrack program under station information. InstantTrack did some calculation and showed me on the screen my grid locator. Today, you can get it even easier by using a GPS and setting it to Maidenhead Coordinates instead of Lat/Long. You can also plug in your address in any of the on-line map programs and get the Lat/Long and then convert them to Maidenhead.

Instant Track needed this information so that it could tell me what direction to point my antennas so I could work a satellite. It also tells me when that satellite will rise and set at my location.

But, what if you have just worked a station, got the QSL card and there is no mention of a grid square. You worked him and you have earned credit for that grid square. There are several programs that you can get from packet or a bbs. They are GRID.COM, GRID.ZIP, GRIDLOC.ZIP and GRIDX.BAS. All of these programs do basically the same thing, the authors just have different whistles and bells. They allow you to input a latitude and longitude and out comes the magical grid square. You can also go the other way, input the grid square and out comes the latitude and longitude.

So, your next question is simple. Where do I get the latitude and longitude of the station I worked. That is not too difficult in the U.S. I use a program called Street Atlas by Delorme. You can also use AUTOMAP by Automap. When you enter the name of the particular city, the latitude and longitude is displayed for you. You can locate any place in the U.S. in no time at all.

For foreign stations, you will have to look in an atlas and figure it out. And finally, the ARRL publishes a World Grid Locator Atlas. This is great if you know a major city near where the station says he lives. Sometimes you get a city that is tiny and will not appear on all maps. Of course, the best thing is to get into the practice of saying "I'm located in EL29, what is your grid square?" Almost everyone on satellite knows theirs. I say almost everyone, because I have worked some people that never bothered to look at the InstantTrack screen and no one ever asked them for their grid square before.

So, there you have it. My grid square is EL29hk. I have worked stations in 427 different grid squares that I have confirmed so far. As you work more stations on satellite, keep track of your grid squares and in no time at all, you will have your first 100 and earn your VUCC award.

Other information:

ARRL information

Wikipedia Reference

US grid squares map from ICOM

Each 4-digit, 1 degree in latitude X 2 degrees in longitude, maidenhead grid division is divided into 24 X 24 = 576 6-digit subgrids. The last two digits designated as subgrids start with "aa" at the southwest corner of each 4-digit grid and finish in the far northeast corner with "xx". The subgrids along the southern-most edge of each grid go from "aa" to "xa", and the subgrids along the western-most edge of each grid go from "aa" to "ax" (see diagram, below). Each subgrid is 2.5 minutes in latitude X 5 minutes in longitude. Whereas the distances represented by these lat-lon divisions are fairly constant for the latitude dimension, the longitude distances vary with latitude. As an example, the southern edge of EL16 (26 deg N lat) is 124.4 miles (200.2 km) across, while the northern edge of EN18 (49 deg N lat) is 90.9 miles (146.3 km). This affects the diagonal distances, of course, as well. The table below shows the variation in grid and subgrid width as well as in the diagonal distances across each.

To download an exellent program to convert between lat-lon and maidenhead grids, and to calculate bearing (including reverse) and distance in miles or kilometers, go to the W4SM site; scroll down to and select "New Improved" WinGrid Ver4.1 (wingrid.exe).

The table below shows the width and diagonal distances for grids and subgrids and how they vary with latitude. These distances were calculated using WinGrid v4.1.

Calculations are NOT +/- 1%, but they are close; the distances showing two digits after the decimal point should most likely be rounded off, e.g. call "5.18" 5.2, "5.14" 5.1, etc.