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   Solarbird :flag_cascadia: (moira@mastodon.murkworks.net)'s status on Sunday, 12-Apr-2026 09:33:38 JST Solarbird :flag_cascadia:

   okay so let's think this out

   I have a UHF antenna at a not well known height pinging a location gmaps says is 1084 meters away (line of sight).

   We'll call the altitude of that location 0m to simplify maths. Openmaps has it on the low side of a 20m line. That matters to get actual altitude at the end; at most, it's another 2-3m down probably?

   At 850m (straight-line) from my 0m location, a signal clears a +70m hill on its way to either end.

   So start at 0m and create a right triangle with the signal path, and 70/850 should be the tan() of the angle from the 0m point. Therefore 70/850 = X/1084, and doing the maths gets you X = 90m.

   90+20=110m, ish.

   But my best direct estimate from the same topo maps is 93-95m.

   #gmrs #AmateurRadio

   • Doughnut Lollipop 【記録係】:blobfoxgooglymlem: likes this.
   • Embed this notice
     Solarbird :flag_cascadia: (moira@mastodon.murkworks.net)'s status on Sunday, 12-Apr-2026 09:34:57 JST Solarbird :flag_cascadia:

     in reply to

     • AN/CRM-114

     @flyingsaceur That's (part of) the thing that causes picket fencing, innit? Or am I conflating things that I shouldn't be conflating?

     anyway that diagramme is helpful thanks, it's a bigger angle add than i expected!

     Doughnut Lollipop 【記録係】:blobfoxgooglymlem: likes this.
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     AN/CRM-114 (flyingsaceur@ioc.exchange)'s status on Sunday, 12-Apr-2026 09:34:58 JST AN/CRM-114

     in reply to

     @moira ACHIEVEMENT UNLOCKED: knife-edge diffraction

     https://www.raymaps.com/index.php/knife-edge-diffraction-model/

   • Embed this notice
     Solarbird :flag_cascadia: (moira@mastodon.murkworks.net)'s status on Sunday, 12-Apr-2026 09:34:59 JST Solarbird :flag_cascadia:

     in reply to

     Being at +93ishm _does_ clear the +70m hill (90m actual) but not at an angle that should let me see the 0m points - but I do.

     So.

     Bouncy signals? Bad maths? Weird RF-over-angle behaviours? (Same kind of thing gets you picket fencing)

     I dunno.

     hm

     I don't think I'm fucking up my maths but am I?

     Or is this "don't mix google maps and open maps it only leads to pain"?

     #gmrs #AmateurRadio