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IO91pm download for Windows

Free download IO91pm Windows app to run online win Wine in Ubuntu online, Fedora online or Debian online

This is the Windows app named IO91pm whose latest release can be downloaded as io91pm-20230404.tgz. It can be run online in the free hosting provider OnWorks for workstations.

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Keywords: Hamradio, Radio-amateurs, Maidenhead-, QTH-, (QRA-), Locator, Distance and Bearing Calculator, GNU/Linux command-line, LaTeX,- UTF-8-, ASCII-output, GPLv3; based on GM4ANB's book.

"IO91pm is the Maidenhead-Locator for Maidenhead"

* For another little project, I wanted a QTH-Locator calculator for the UNIX (GNU/Linux, bash) command-line.
* There are many, some very good, online QTH resources, but I wanted something that would work off-line.
* There are also several GUI- (Windows-, X11-, etc.-) based calculators, but I wanted something for the command-line, something that could also be used in (bash-)scripts.
* The repository for my GNU/Linux distro has only one such a QTH-calculator.
--- This program has a few issues
--- Made worse by the adaption for Ubuntu, that removed half of its functionality
So, I had to roll my own. (Which I enjoyed anyhow.)
Perhaps also useful for others


  • Proper support for 2, 4, 6, 8 or 10 character locators. A 10 character locator specifies a cell of more-or-less the size of a house.
  • The program accepts "dirty" locator strings that might be produced by databases, such as "Berlin JO62" or "IO91iq84po near Oxford"
  • Calculations from cell-center (instead of south-west corner, as some programs do). This is especially better when computing between locators of different resolutions (locators with different number of characters).
  • Distance calculation based on the best of GM4ANB's algorithms (instead of the simplest, as some programs do). The simplest algorithm can introduce an error of up-to a hundred meters within a relatively small, flat and low-lying, mid-latitude area such as the Netherlands. The best of GM4ANB's algorithms computes distances that fit, within a few meter, to the Dutch national grid reference system, the "Rijksdriehoekscoördinaten" system.
  • This program reports an error estimate.
  • When renaming the program (or creating a (soft-) link to it) with as new name a valid QTH locator, then distance calculations will be done from that locator.
  • The program can produce LaTeX output.
  • For further details, see: http://pe1aqp.krom.eu/software/IO91pm
  • And, lastly, the code uses τ (tau) instead of π (math pi).


End Users/Desktop

User interface


Programming Language



TeX/LaTeX, Ham Radio

This is an application that can also be fetched from https://sourceforge.net/projects/io91pm/. It has been hosted in OnWorks in order to be run online in an easiest way from one of our free Operative Systems.

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