Can someone point us to an online site that can determine if two locations are line of sight to each other, taking the terrain in between them into account?
Thanks!
Orv
W6BI
Thanks!
Orv
W6BI
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Andre, K6AH
Orv W6BI
https://airlink.ubnt.com/#/
Here down south we have lots of very tall pine trees that cause attenuation (maybe due to reflections and scattering of the signal?) So, we think these tools are a bit optimistic. Maybe they work well in some areas, like out west where there isn't as much vegetation and what's there is very dry.
So, I'm wondering if anyone has compared actual results maybe in terms of actual received signal strengths in dbm compared to predicted? I plan on taking a portable node to a tailgate gathering this weekend to see if the AirLink prediction is anywhere near reality. The tool says I have an unobstructed 12 mile path to the site and should see -74.6 dbm on each end at 2.4 GHz. I plan to compare that to the value observed on the node status screen if I am able to make the link.
73,
Ron N4RT
Bromley, AL
Radio Mobile can be modified to give more realistic results on 2.5 and 5.8 GHz see my post under:
http://www.aredn.org/content/question-about-radio-mobile-link
One party reported that at 3.4 GHz the attenuation of trees is about 20x's what RMW predicts (as in 40 dB instead of 2).
If you put in the numbers suggested by the CCIR 236-2 model, you end up with a RadioMobile coverage map that looks very much like a line-of-sight map.
Or, if you do a point-to-point link, you see the signal drop off dramatically as the path gets into the (modeled) trees and other "clutter" while you adjust the antenna heights.
The ITU have done a lot of measurements:
https://www.itu.int/dms_pubrec/itu-r/rec/p/R-REC-P.833-8-201309-I!!PDF-E.pdf
The kind of attenuation they show for any significant penetration of vegetation exceeds the allowable loss margins for the kind of equipment AREDN uses (something we already know).
In round numbers you might consider 1-2 dB/m at 2.4 GHz and 2-3 dB/m at 5 GHz, but the attenuation varies quite a bit with the species of tree and density of vegetation.
In addition to attenuation of the signal magnitude, there are other deleterious effects like loss of polarization and loss of phase coherence. This is because one of the mechanisms of propagation through trees is forward-scattering, Leaves and twigs that are about 1/2 wavelength have the biggest impacts in that regard.
I use
heywhatsthat.com
It does not consider trees, but you can inspect the route in detail and find trees and other non-terrain objects that may be in the way.
Save the URL of your map and you can use it again and again as needed or share it with other people.
Another interesting observation, though, was that the sun was on almost the exact same azimuth and when it rose above the tree tops (at about 0900) it completely killed the link. I got no SNR and the screen showed N/A. I played with the azimuth of the NSM2 antenna to see if I could get the -90 dbm signal back with no luck. So, the noise floor must have increased to the point where it masked the weak signal from the home QTH node due to looking right into the sun! Has anyone else observed this? It kind of surprised me that the noise from the sun would have that much effect but I know these nodes are not designed for weak signal work.
A fellow ham had used Radio Mobile which apparently does take into account some attenuation due to vegetation and it predicted about -90 dbm signal... which was right on the money in this particular case. We will continue to test and see how the real world here compares to predictions using these tools. I'm sure the results will somewhat depend on the area and amount/type of vegetation involved.
73,
Ron N4RT
I used to use the sun to peak up my EME antenna (which had about 27 dB of gain, similar ot some BBHN antennas).
Of course that was at 432 MHz not 2400.
But I note that they use the sun's radio noise at 2800 MHz for solar flux measurements. The so-called 10.7 cm solar flux average is a good proxy for the number of sunspots (using some conversion formula).
The flux is measured in SFU which is 10^-22 W/m.sq-Hz (look it up).
If I did the math right, 100 sfu at 20 MHz BW roughly works out to -117 dBm/m.sq
A two or three foot dish could easily receive this, if the receiver had typical noise figure that you see at weak-signal stations.
But to get the signal up to where a Rocket M5 could see it, I think you would need a bigger dish ;-)
Below left is an airlink.ubnt.com simulation using 2.4GHz at 5MH width total distance 11km (7 miles). I think the Access Point will be a 20dBi AIRGRID M2 AG-HP-2G20 and the station is a 11dBi NANOSTATION M2.
To the right is the station looking down toward the access point. The signal should be above the heavy tree line just over the roof down the hill. There should be no other trees in the way up to very near the access point on the other side. Well maybe some trees at the 2.25km from the left hill? This area has many rolling hills with trees as tall as 100 feet high.
Does anybody want to put any input if they think this will or will not work out?
Hopefully this will be testing in the coming weeks and I will post the results.
-Bob in NNJ
1) if this is a new deployment of AREDN, you may want to check the other bands to see if they will show better signals. (ie. 3Ghz, 5Ghz)
2) you want a more accurate model, try RadioMobile. (airlink is a decent 1st pass, but, RM is better as it will take the treeline into consideration.
Before I heard about "airlink.ubnt.com" I attempted to use "RadioMobile". Found it at: "http://www.cplus.org/rmw/download/download.html". I tried to install it using their directions. You have to create directories and unzip files to certain assumed locations. Directions are not as clear as I would like them. I am a very detailed oriented person and much in the directory structure and setup (editing Map_Link.txt files) is not totally clear. I tried for hours to get RadioMobile to work. They should just create an install exe file to extract and set all this up for you. Should not be that difficult to create a setup exe file if one knows where everything goes.
So I could not get "RadioMobile" to show a map and gave up after I was told about "airlink.ubnt.com". I originally was using "HeyWhatsThatPath". "airlink.ubnt.com" looks good enough for now and is an easy tool to use.
I would like to use the more powerful analysts of "RadioMobile" but will have to try to decode the instructions again.
BTW: The instructions on how to download, install, and setup an Ubiquiti devices for AREDN done by WU2S is very comprehensive and a job well done with screen shots! Took under an hour to do my 1st one with those instructions.
-Bob
Keith
Thanks, I'll have to look into that.
I also found a self installer at: "http://www.g3tvu.co.uk/Quick_Start.htm" 1/4 way down the page 'Radio_Mobile_Setup.zip".
I'll have to try this out.
I have used Google Earth to visually see the line of site from one location to another. The elevation of the antennas from ground has to be the same at both sides the way I do this. This only does line of site. You will need to mentally put in the fresnel zone.
1. Download "Google Earth" and run it.
2. Turn off all "Layers" at lower left for now. You may want the "Roads" enables to figure out were you are?
3. Find location #1 by zooming in. You can use controls on the top right or a mouse with wheel.
4. Once zoomed in make sure you have a straight up view by using the upper up/down/left/right control and press down until the view is straight down.
You may need to reposition using lower up/down/left/right control. If so you will need to use the top control down to review looking straight down again.
5. With the #1 location zoomed in while looking straight down select on the tool bar the 3rd tool "Add Path" then using mouse select the point of location #1.
The "Google Earth - New Path" popup will come up and you can move it if it is in your way. You will use this popup later.
Now you CAN NOT use the mouse to manipulate the view as it will then add more path points. You can use the mouse wheel only to zoom in and out.
6. Use the controls on the right to get to your #2 location.
7. Once at you destination location #2 again use the top U/D/L/R control Down to have the view looking straight down and click the location with the mouse.
NO MORE CLICKING on the map as this will add more path location which you do not want.
8. Now go to the "Google Earth - New Path" popup and go to "Altitude".
9. In "Altitude" where is says "Clamp to ground" select "Relative to Ground", then add the "Altitude" in meters that the antennas are at.
You can only pick one altitude. It would be great if at each location different altitudes could be picked as the line of site to be drawn.
10. I like to use a bit thicker of a line and better color. Go to "Style, Color" and select "Color:" bright bellow and "width" 2.0.
11. Select "OK" and you will have a bright yellow line from location #1 to #2.
12. Now you can use your mouse to manipulate the view. Zoom out with the wheel and move the view around with a left button drag.
13. Now the 3D stuff. On "Layers" at the left menu enable "3D Buildings. You can turn off "Roads" if you like.
14. Where the bright yellow line disappears is in the way of the line of site. Remember you will need additional room for the fresnel zone.
15. By pressing down the "shift" key and dragging on the view the reference point of the view can be changed to a lower angle.
16. Now you can look and see what is in the line of site way of the signal. You can even get views from street view looking up at the line of site.
Note that sometimes Google Earth can get confused at what you are trying to view and may put you at ground level and other strange view. Before manipulating the view you may want to save your work.
Have Fun Looking Around your RF path!
Example with trees in the way. The road may also be in the fresnel zone.
How cool would it be to add the connection paths that are made with AREDN nodes to the ARDEN "Google Earth" KML files?
Then people could review the know good paths against what they are trying to connect with.
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There is a 3D fresnel zone "Google Earth" KML file creator at: https://www.loxcel.com/3d-fresnel-zone
Cost is $10 for 4 in 4 days or $100 for 100 within 12 months