David,

? lon = (gps.location.lng() * 100000) + 18000000L;

? lat = (gps.location.lat() * 100000) + ?9000000L;

is taking a longitude as a decimal number from -180.000000 to +180.000000 (or something very close to that) and turning it into a positive integer
by scaling it up, by multiplying by 100000, and then adding 18000000.? So now the range of longitudes goes from 000000000 to 36000000.

(Multiplying by 100000 is equivalent to shifting the decimal point five positions to the right and so it "preserves" the first five values to the right of the decimal point, in the original number, in the scaled integer representation.)

It then does a similar calculation for latitude which starts out with a range of -90.00000 to +90.00000 and transforms it to a range of 0000000 to +18000000

Next what it's going to do is divide those scaled positive integer lat/lon in order to generate the codes for the grid/subgrids.

The first step is to calculate the first two values of the locator code by dividing the longitude into 20 degree sections and the latitude into 10 degree sections.? In our scaled representation, 20 degrees is represented as 2000000 and 10 degrees is represented as 1000000.? The longitude values get mapped to character (letter) values from 'A' to 'R' (the first 18 letters of the alphabet).? Since longitude is represented as a range of 0 to 36000000, if we divide that by 2000000, that's equivalent to dividing 360 by 20 = 18.? So you are getting 18 possible values based on which 20 degree section of longitude you location is in.

In case you don't know, the "+=" operation in C means "take the value on the right and add it to the value on the left and store the result back in the variable on the left.? So in the line:

MH[0] += ?lon / 2000000;

It's going to look up the zeroth entry in the MH array, which is an ascii number representing the letter 'A' and add to it a value from 0 to 17 based one which section of longitude falls into.? The result will be that MH[0] will hold an ASCII code for a single latter in the range from 'A' to 'R' depending on the longitude value of the location.

The does the a similar operation in the next line of code:?

?

void loc8calc() // Calculates full locator from GPS

{

?

? lon = (gps.location.lng() * 100000) + 18000000L;

? lat = (gps.location.lat() * 100000) + ?9000000L;

?

? char MH[8] = {'A', 'A', '0', '0', 'A', 'A', '0', '0'}; // Full locator characters

?

? MH[0] += ?lon / 2000000;

? MH[1] += ?lat / 1000000;

? MH[2] += (lon % 2000000) / 200000;

? MH[3] += (lat % 1000000) / 100000;

? MH[4] += ((lon % 200000) / 8333);

? MH[5] += ((lat % 100000) / 4166);

? MH[6] += ((lon % 200000) % 8333) / 833;

? MH[7] += ((lat % 100000) % 4166) / 416;

The resonator should be bigger. Or the PCB footprint smaller. I came up with the BOM, see below:

Thanks for this thread, I working the same path, and this helps a lot !