Radio Distance V2.0

This is a trivial program which calculates the distance and the bearing between two points. Points are either entered as geogr. data (Latitude/Longitude) or as qth-locator in the Maidenhead format (6 or 8 digits), as used in ham radio.

Output is in degrees [°] for bearings, in Kilometer [km], US statute miles [mi] or nautical miles [nm] for distance.

Version 2.0 - (09. July 2000)

Version 1.4 - (20. May 2000)

RadioDistance is freeware, designed for Windows95/98 only and in english. If you like it i would appreciate an email to ep (at), also for suggestions for improvements, bugs etc...

Somewhen my harddisk crashed, for real. And I had no backup... I was able to recover most of the sources for my programs from other sources, but not for this program -RadioDist. So changes and further improvements are unlikely to happen unless I write it again from scratch.
Let this be a warning to you - make backups!



Just delete radiodist.exe.

If you really want to clean up, delete the registry key:


Be careful when editing manually your registry...


After starting the program, select the setup screen:

rdset2.jpg - 56216 Bytes

Select the unit for distances (km, mi or nm), select whether locators shall be calculated with 6 or 8 digits; select whether the resulting geogr. coordinates should be centered to the square or not.

GPS Setup

If you want to use a GPS device, select the GPS tab.

rdgps2.jpg - 72407 Bytes

Here you can select the serial port (COM) where the GPS device is attached (COM 1 to 4) and the speed (baudrate), 1200, 2400, 4800 or 9600. Most GPS I have seen use 4800 Bd. The GPS device must output standard NMEA messages, only the NMEA message "$GPGLL" is required, all other are ignored.

During GPS use, the last 4 received messages are shown on this page in the NMEA monitor.

Select whether the GPS position should be used as starting position, ending position or off. Using it as start could be useful if you are moving in a car or boat and want to know the bearing to a fixed target all the time. Used as destination position could be useful when tracking a moving target, assuming that the NMEA data is coming via some link, maybe APRS.

During GPS use, the received data is entered in the various fields on pages "Lat/Lon" and "QTH Locator". Only the other position, which is not provided by GPS, can be edited. Calculation happens automatically whenever a new GPS message is received. If the GPS data is invalid, the last received position is shown.


In manual mode (non GPS) enter the two positions either in Lat/Lon format or Maidenhead QTH locator format, then hit enter or click on the "Calculate" button. The results (distance, bearing) are shown in the various fields.
During GPS mode, only one position can be entered manually, the other is provided by the GPS data. Calculation happens automatically whenever a new, valid GPS message is received. The position (start or destination) which is provided by the GPS is marked with GPS.

rdlalo2.jpg - 68981 Bytes rdloc2.jpg - 59156 Bytes


The Maidenhead locator system was invented to facilitate the exchange of position between two radio amateurs. Under the requirements that the system should be a) useable worldwide and b) the data to be exchanged as short as possible, some sacrifices to precision had to be made. Usually we use the 6-digit locator (i.e. JN49kw subsquare). Be aware that this "position" is highly inaccurate! A subsquare is 5' wide and 2'30" high. That amounts to an area of roughly 6km by 4km (at 47N, even larger when closer to the equator). For this reason i have included the possible error in the resulting geogr. positions on page "QTH Locator".

To get better precision, you need more data. That's the reason for 8-digit locators (i.e. JN49kw17 sub-sub-square), mostly used for UHF/SHF applications. Here the precision is tenfold, i.e. the sub-sub-square is only 630m x 430m.
If you need real good precision, use geographical Lat/Lon data, if available.

Many thanks to Robert, DK7NT who helped with his suggestions at improving this program.

Download the zipped file (280 KB)