I am thinking about a solar powered offgrid solution with a LoPy as a single channel gateway. Thus the lighting protection would simply be a pole (higher than the antenna) and that pole is mounted on my metal balcony guard railing.
Due to the WLAN connection to my network, there is also no connection to anything. That should be save enough. If anyhow the lighting hits the antenna, it should go to the pole and that is shorted to the balcony guard railing.
If I put the antenna below the railing, the railing it self is the highest point that gets hit first.
I think, that should work. A proper dimensioned solar module is another issue (I start with a 20W module and a 2500mAh LiPo)
And the SMA cable solution is a different option without an offgrid scenario.
The most important part of lightning protection is grounding. Then comes grounding. And then comes grounding. Grounding however means: running a dedicated, large gauge (16mm² cross section and up) copper wire from the lightning protection to several grounding rods in the ground around your home. If you can't do this, forget about lightning protection altogether.
Why DC grounded antennas are no good for lightning protection, even though (mostly Chinese) manufacturers make that claim, is that they shunt the EM lightning energy away to the common ground, damaging or destroying everything that shares a connection to this ground. Your gateway for sure, maybe even your home appliances (through the earthing pin) or your router (thorough the ethernet cable). If they shunt altogether, because the DC grounding circuit is just a small resonant circuit that will never survive a lightning strike and possibly not even a nearby strike.
If you are unable to provide the large gauge dedicated grounding wire, then forget all about lightning protection. Any other measures will just give a false sense of safety.
But like @BoRRoZ says, you shouldn't lie awake from an unprotected LoRaWAN antenna either. In Europe you have on average 2 to 4 lightning strikes per km² per year. Most of them hit ground directly. The chance of one hitting your antenna is incredibly low, especially if there are other structures in the vicinity.
A completely off-grid gateway is the best lightning protection there is. Putting other poles in the vicinity and connecting them to other metal structures is a very bad idea and will negate the lightning safety of your off-grid solution. You should actually even increase the insulation between your gateway and your building, e.g. by putting it on a rubber mat. This will make your gateway 'invisible' for lightning.
In general, it is always a bad idea to put lightning rods in the vicinity of antennas. The near field effect will negatively affect the performance of the antenna.
Found some other cheap antennas on Alibaba, maybe we should start a buying group. If you order 5, they only cost 10 dollar a piece! (they don’t ship a single one even though the page says so, I contacted them).
I’m in if some others want to buy one for cheap :).
very cheap indeed, but I think it's easier buying together within the same community / city, another possibility is that you contact the supplier again and ask him for a special TTN discount and that he can use this topic to promote his antenna for a special TTN user price
If we do group ordering, than we'd better order decent antenna's from reliable brands. I have yet to see an Aliexpress/Alibaba antenna that actually has some gain at all, despite being advertised as one million dBi .
indoor antenna's close to double glazing, or in low energy buildings, can be a problem (losing 10-20 db) there is not much info to find on the net .. so try it yourself.. place the indoor antenna a few meters away from the window