The Maidenhead Locator System

Locator systems were developed in Europe primarily to permit Amateur Radio operators to measure the distance they were able to communicate on VHF frequencies. Prior to this they were using standard Geodetics (longitude and latitudes) but all those numbers were difficult to transmit and receive on both voice and CW.

Numerous articles have been written describing the evolution of our present system, The Maidenhead Locator, so I won't go into a lot of detail. I have included links at the end of this article for those interested in reading more about the evolution.

By the mid-seventies there was sufficient interest world wide to develop a system that could be used in all regions and at one time there were more than 20 systems being considered. Finally, in 1980 in Maidenhead, near London, at a VHF working-group meeting, it was decided to adopt a single system that could be used world wide and this system became known as the Maidenhead System or simply "the locator".

The Locator represents a position on the Earth based on latitude and longitude. The system deliberately limits the precision so that a minimum number of characters are needed to describe a position using voice or Morse code. The following table illustrates the difference:

Geodetic Position	The Locator
long:122.2844W lat:38.2977N	CM88uh

While it is obvious that the data provided by The Locator would be much easier to transmit (and receive) what might not be obvious is the fact that most of downtown Napa is also located in square CM88uh while the position described by the geodetic coordinates describes a very small area. For our purposes, that's just fine.

Some interesting details

Unlike our conventional system of Latitude/Longitude (Geodetics), the Locator System begins at the South Pole at the Prime Meridian (180^o or the International Dateline), and builds Northward and Eastward ending back at the Prime Meridian at the North Pole, but on the East (opposite) side of the dateline.

I know, at the Poles there is no East or West.

The first grid square is AA00aa (probably not many stations there) and the last grid square is RR99xx (also sparsely populated)

By definition each "Field" which is represented by the first two letters is 20 degrees wide by 10 degrees high. At the equator, therefore, each Field, is about 1,380 miles wide. Since there are 18 of them they are identified as A through R. At our latitude, each Field is closer to 1000 miles wide and up at latitude 49 (the Canadian border) they are about 990 miles wide. Nearing the Poles, the Fields are triangular, being approximately 250 miles wide along the 80th parallel and tapering to a point at the exact center of the Pole. The Fields are all approximately the same "height" (distance from South to North) about 690 miles.

The first alpha character represents the longitude and the second alpha character represents the latitude. For example, we are in Field CM. "C" begins West of us at 140^oW and changes to "D" just 2^o East of us at 120^o, just West of Reno. "M" is our latitude. Every Field between 30^o and 40^o N will have "M" as the second Alpha designator.

Each of the 324 Fields which cover the surface of the earth are subdivided into 100 squares, each of which is 1^o of Latitude and 2^o degrees of Longitude. These squares are numbered 00 through 99 using the same pattern as the Field, i.e. the lower left corner upward and to the right. Here is the layout of the numbering of the squares within any Field:

09	19	28	39	49	59	69	79	89	99
08	18	28	38	48	58	68	78	88	98
07	17	27	37	47	57	67	77	87	97
06	16	26	36	46	56	66	76	86	96
05	15	25	35	45	55	65	75	85	95
04	14	24	34	44	54	64	74	84	94
03	13	23	33	43	53	63	73	83	93
02	12	22	32	42	52	62	72	82	92
01	11	21	31	41	51	61	71	81	91
00	10	20	30	40	50	60	70	80	90

Since the Fields at our Latitude are nearly 1,000 miles wide, each square is about 100 miles wide

For additional precision, each of the above Squares is divided into "Sub-squares" using identifiers aa through xx. In the US and UK, These identifiers are shown in lower case although you will see many examples using upper case. Here is a portion of a Square, divided into Sub-squares. Only the lower left corner is shown for brevity.

ad	bd	cd	dd
ac	bc	cc	dc
ab	bb	cb	db
aa	ba	ca	da

Each Square is divided into 576 Sub squares (24x24) each of which is 2.5 minutes longitude and 5 minutes latitude. At our latitude this equates to about 4.2 miles wide. The entire system is devised so that no sub square is more than 12 km or 7.2 miles from one corner to the other diagonally. Grid squares are used extensively in microwave communication and measurements are made using the center of the square or sub-square.

If additional precision is required, the sub-squares can also be divided and then those sub-sub-squares can also be divided. The protocol requires using alternating pairs of Alpha-numerics. For the purposes of Amateur Radio however, 3 pairs of characters work quite well. To add more precision one might be better off just using Geodetics.

Links

This one is really cool. It uses Google maps and lets you find the grid square of any point on the globe by clicking on the map. It has some limitations, and the Geodetics are off a bit due to rounding but it's a useful tool. F6FVY Grid locator

ARRL Web: Grid Locators and Grid Squares

ARRL Web: A converter. Input your lat/long, find your square

From one of the original developers: By Folke Rosvall, SM5AGM

AMSAT: By Bruce Paige KK5DO, AMSAT coordinator

And the best of all: The DX Atlas This is a really neat program that has lots of goodies such as beam headings, prefix lookups, Grayline maps, and much more. As you move the cursor over the map, the coordinates tool bar updates with lots of data such as grid squares, beam headings, long path distances and more. 30 day free trial and well worth the money to buy if you DX.

This months trivia question: In 1984 the now Governor of California starred in a movie with Linda Hamilton. The name of the movie is a very important term to Amateurs who operate HF. What is the term and why is it important? email your answer to the editor

09	19	28	39	49	59	69	79	89	99
08	18	28	38	48	58	68	78	88	98
07	17	27	37	47	57	67	77	87	97
06	16	26	36	46	56	66	76	86	96
05	15	25	35	45	55	65	75	85	95
04	14	24	34	44	54	64	74	84	94
03	13	23	33	43	53	63	73	83	93
02	12	22	32	42	52	62	72	82	92
01	11	21	31	41	51	61	71	81	91
00	10	20	30	40	50	60	70	80	90

09	19	28	39	49	59	69	79	89	99
08	18	28	38	48	58	68	78	88	98
07	17	27	37	47	57	67	77	87	97
06	16	26	36	46	56	66	76	86	96
05	15	25	35	45	55	65	75	85	95
04	14	24	34	44	54	64	74	84	94
03	13	23	33	43	53	63	73	83	93
02	12	22	32	42	52	62	72	82	92
01	11	21	31	41	51	61	71	81	91
00	10	20	30	40	50	60	70	80	90

09	19	28	39	49	59	69	79	89	99
08	18	28	38	48	58	68	78	88	98
07	17	27	37	47	57	67	77	87	97
06	16	26	36	46	56	66	76	86	96
05	15	25	35	45	55	65	75	85	95
04	14	24	34	44	54	64	74	84	94
03	13	23	33	43	53	63	73	83	93
02	12	22	32	42	52	62	72	82	92
01	11	21	31	41	51	61	71	81	91
00	10	20	30	40	50	60	70	80	90