SMP range page update

Following an enquiry from one of our colleagues in the US, the range page has been updated with some new functionality.

In addition to the standard option of finding summits within a closed circle, the page now offers the possibility to find summits within an open ring area, defined by inner and outer radii.

This will apparently be of some use to the US SOTA microwave activists, or to those on VHF/UHF with low power.

Users will need to force a refresh (Ctrl+F5 or similar) in their browsers to load the new code.


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Great stuff. Thanks very much Rob.
Best wishes

Thanks Rob for a really quick implementation of this functionality. For those who want to analyze path losses and a line-of-sight terrain analysis, see SPLAT! A Terrestrial RF Path Analysis Application For Linux/Unix

“SPLAT! is an RF Signal Propagation, Loss, And Terrain analysis tool for the electromagnetic spectrum between 20 MHz and 20 GHz.” You can calculate the probability of your comm path, especially helpful for the SOTA microwave enthusiasts.

Thanks again Rob!


I have found what I consider to be a more user friendly web-based calculator for line-of-sight distances between two points.

See . Lots of great information here plus it uses google earth as the underlying engine for terrain vertical analysis.

IMO, much more user-friendly than the SPLAT recommendation with more information. Ideal for SOTA VHF and microwave enthusiasts.

A perfect adjunct to Rob’s SMP Range tools.


Is there any stopping this Guy? Well done again Rob

  • as well as VHF/UHF/SHF usage, I have a HF use for this feature.
    If I know the current skip distance on a band I can put that in and see how far away from the summit I need to be before I might hear the activator! So often I see spots for DL and OE stations, hear chasers working them at 5-9 but I hear nothing because I’m too close!

73 Ed.

Another addition, not only to the range page, but also the main page: a fun tool to quickly measure S2S distances on the map.

To use the tool, first find your summits, and then activate the small “tape measure” control at the bottom left of the map area.

Mark the summits, the distance between which you wish to measure, by:

  • left clicking the first,
  • right-clicking the second

With any luck :smiley: the result should be displayed in the table next to the “tape measure” control. As always, a forced refresh of the browser will probably be necessary to load the new code.


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Hi Rob,
I’m guessing the distance is the mapping distance, not “great circle” distance? Not an issue with S2S within Europe but S2S EU <> VK would be a little off I guess and I expect it would have to be the short path distance, not the long path one?


Hi Ed,

By “mapping distance”, do you mean the distance on the flat? - i.e. some kind of distance computed from the flat representation of the mapped area as “stretched out” onto the 2D plane? Then the answer is no.

There are a number of options I could have used, and in fact I’m using the simplest of all for this fun tool, which is a great-circle distance on a spherical model earth, where the radius is set at 6378137 meters. With just a little more effort, I could - in addition to spherical great-circle - give the user the option of using one of the following calculation methods:

  • Haversine
  • Cosine Law
  • Vincenty (most accurate)

However, I thought I’d go with the easiest at this stage. Now I see I’ll have to provide these options for the more discerning of my users :wink:

I’m also rounding off distances to the nearest 10 meters - this should probably be set to the nearest millimeter for those requiring more accuracy. Or do I mean precision?


Hi Rob,

Yes I meant the flat earth measurement - Great Circle even based on a spherical earth will give a pretty accurate representation even on DX S2S range calculations.

Nearest 10 metres - you’re kidding right? Nearest KM is probably OK!

If we assume the earth is a perfect sphere rather than being roughly pear shaped, we could approximate long path distance by - workiing out short path and then subtracting that from the circumference of the spherical world to give the long path distance.

73 Ed.

Ed, I hadn’t even considered short/long path, since for me in this particular context it holds no interest. I’m indebted to you, however, for giving me a clue as to how this might be calculated.

It has to be said, however, that the SMP and its’ maps, like ham radio itself, is a toy,

a flim-flam, and does not represent the real world.

And, I’m not a little amazed that anyone would even imagine a flat earth distance calculation to be considered for such an application, let alone implemented.


Same algorithm the database uses for S2S distances. I used the WGS84 value for the Earth’s radius of 6371km. I don’t even both rounding the doubles when converting to ints, I just truncate them with the answer displayed in kms