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# Thread: Horizon line of sight

1. ## Horizon line of sight

My ground level elevation is about 1400 ft above sea level. I have a 180 degree view of all the land to the north of my location. The avg elevation of the land to the north is approx. 950 ft above sea level. As you can imagine I have one heck of a view to the north.

My question is, how can I determine the line of sight distance to the horizon?

2. Some mathematics is involved, especially since the earth is a sphere !

THIS is the quick graph -- looks like 20 miles to north.
http://en.wikipedia.org/wiki/File:Ho...he_horizon.png

Distance to horizon
http://en.wikipedia.org/wiki/Horizon

Line of sight propogation
http://en.wikipedia.org/wiki/Line-of-sight_propagation
Last edited by W9GB; 08-10-2012 at 01:02 AM.

3. LOS applies to your eyes and maybe binoculars or a telescope, but doesn't apply well to radio frequency work.

Are you trying to determine what you can "work" on VHF-UHF-SHF-EHF? Or just how far you can see?

4. Ham Member
Join Date
Jan 2000
Posts
33,432
For r.f., the "line of sight" is right at 33.333-percent beyond the visual "line of sight". Of course, in the "real world", there are all sorts of terrain features, and other things, that do limit the actual r.f. and visual "line of sight".

Glen, K9STH

5. For VHF/UHF propagation, there's a neat tool out there online called SPLAT!. You sign up and provide your coordinates, then SPLAT! uses that information to plot your coverage based on terrain. I've found that it's remarkably accurate, showing distant hilltops where people can work me direct on simplex. We've also plotted our local repeaters that way, and SPLAT! does a great job of showing shaded areas and holes in the coverage. You can also map the SPLAT! results on Google Earth maps, making it even more interesting.

6. Originally Posted by WB2WIK
LOS applies to your eyes and maybe binoculars or a telescope, but doesn't apply well to radio frequency work.

Are you trying to determine what you can "work" on VHF-UHF-SHF-EHF? Or just how far you can see?
I once had a 100ft tower at my location and my vhf/uhf coverage was fantastic. Almost to good as I had to reduce power so that I wouldn't interfere with Hams talking local up in Ohio (well over 100 miles away) even at 5 watts on my homemade 7 element beam.

I am just starting to gain interest in amateur radio after being non active for about 5 years. I no longer have the 100 ft tower and plan on only running a ground plane mounted on the roof. I am interested in trying to figure out what type of coverage I can expect with just the ground plane. I understand there are many other things that can and do affect radio range.

7. Originally Posted by K0RGR
For VHF/UHF propagation, there's a neat tool out there online called SPLAT!. You sign up and provide your coordinates, then SPLAT! uses that information to plot your coverage based on terrain. I've found that it's remarkably accurate, showing distant hilltops where people can work me direct on simplex. We've also plotted our local repeaters that way, and SPLAT! does a great job of showing shaded areas and holes in the coverage. You can also map the SPLAT! results on Google Earth maps, making it even more interesting.
Thanks for the tip on SPLAT!. I had heard of it but also had forgot about it until your reply. I will most definitely give it a try.
Thanks

8. Here is a link that might help you. Waaaaaaaaaaaaaaay back in the boy scouts, we did something like this. Close enough for government work.

http://www.wikihow.com/Calculate-the...to-the-Horizon

9. Ham Member
Join Date
Mar 2011
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Silicon Valley
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Here's an easy to use path profiler.

http://www.heywhatsthat.com/profiler.html

10. Ham Member
Join Date
Jan 2000
Posts
1,853
Originally Posted by W6RZ
Here's an easy to use path profiler.

http://www.heywhatsthat.com/profiler.html
Yes it is easy. It isn't measuring elevation of the land. It's measuring elevation of everything. I can see that it is measuring to the tree tops on my property. It shows a terrain difference of 75 ft across my driveway when the elevation of the land changes about 10 to 15 ft. That's because there are some tall thick trees at one end of the driveway. Maybe that's what it is supposed to do?

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