Very long distance LoRa reception normally relies on line of sight communications.
The difference between the distance you can get between two LoRa devices at ground level in an urban area and line of sight, ground to high altitude balloon for instance, is in the region of 1000:1. At a height of 30km a high altitude balloon has line of sight over a very large area, at 30km height the radio horizon is 714km.
Ocaisionally there can be atmospheric conditions that break the normal rules, so whilst you may normally only get 10km or so in these rare conditions reception could stretch to hundreads of kilometres.
We recommend using SF7. This provides us with a map of “worst case” coverage. Due to the 1% duty cycle limit on transmissions, using the fastest spreading factor will maximize the number of measurements taken.
From experimentation it has been seen that slower spreading factors (like SF12) does not perform well when the device is mobile. This is likely due to path fading from obstacles in the radio path, causing bursts of interference (erasures) which the forward error correction can not deal with. When you are doing measurements while standing still higher spreading factors (SF9-SF12) will work, but when mobile it’s better to use SF7.
So, the SF9 you used at the point below is not strictly forbidden, but not using SF7 might be confusing when others are using the map to evaluate gateway coverage? And I even see SF11 and SF12 for other points on your map?
Yes, @arjanvanb makes a good point above that SF7 normally works better for mapping coverage. But it’s not a problem using slower SFs.
I don’t see anything obviously wrong with the data. A good next step would be to draw an elevation profile for those long links and see if it is possible taking line-of-sight and knife-edging into account. The other option is that you were lucky and experienced tropospheric ducting. Or maybe reflection off of aeroplanes, but that is highly unlikely with the time-on-air of SF9 and up.
My feeling is that there might be some reflections that helps this radio path to work. Any chance you can try this experiment again?
Looking at the timestamps of the measurements around the city of Melk it seems like you were driving very slowly. That definitely helped the slower SFs to work.
My point was merely that not using SF7 is confusing for others, who might not expect people to use worse data rates for mapping. But I guess I’m the only one worried about that.
thanks to all of you – very interesting discussion and good recommendations – i agree with the elevation profile that it cant be possible in straigth line on sight — but — maybe reflections ? … i am not sure about the traffic arround Melk - maybe there was a traffic-jam but its 5 month ago …
The most important one is that the free space loss should be compared with MAPL (Maximum Allowed Path Loss) as a result of the linkbudget. For example: If the antenna gain is having a higher gain than you account for, you have a discrepancy.
Sporadic-E has never been accomplished higher than 250MHz. Over meteor scatter even on 432MHz it is almost impossbile to work anything without having a few hundred watts and a >20dBi antenna setup on both sides. The same for Airplane scatter. I do work with this mode as a HAM on 70cm and 23cm but with huge Yagis (>19Ele). I cannot imagine how this little LoRa Power should reach anything with this little undirected power.
But I guess something: Tropo. Why? There was a quite rare january report of a duct around that date:
hi @elidee thank you for your additions to my previous post. I got carried away in my enthusiasm for these phenomena’s that I lost eye on the mandatory requirement of having enough headroom in the link budget.
I’ll try to give a different approach from a physics perspective, it might be the reason?
Light can bend, it always travels through the “shortest” path, the speed of propagation is temperature dependent therefore weird temperature inversions and stuff like that can make light do weird trajectories. Radio waves are of course light. Therefore mirages can happen. We all know the movie mirage thing in a desert (hot sand --> hot air in surface), there is also an effect called “fata morgana” which usually is related to bodies of water and temeprature inversions (cold air on the surface of water).
Here in Barcelona we have a beautiful effect. Sometimes, Mallorca island can be seen from Mount Tibidabo yet it is not in line of sight. But, every once in a while, this “fata morgana” effect happens and the island can actually be seen yet not being there (it is further, but the image elevates itself).
Now I wonder, if there was a gateway in Mallorca. Could I connect to it during this fata morgana effect from the top of mount Tibidabo? Maybe that’s the reason a certain beautiful girl was crying in the foothills of mount Tibidabo, just outside Barcelona. She recieved a message from Mallorca
My point was merely that not using SF7 is confusing for others, who might not expect people to use worse data rates for mapping. But I guess I’m the only one worried about that.
