So I need to build a decent wireless setup covering 5 buildings on a small island.. Ancient RB in third party outdoor housing gave up after 10+ years and it never gave reasonable signal inside buildings (log cabins) so time to build something that's 2020-worthy.

Situation:
- Small island (250x100m) full of pine trees and junipers
- LTE 30-80Mbps "uplink" in "main" building
- 5 buildings all built from thick round pine logs (excellent for signal attenuation...)
- 20-30 Mbps bandwidth from buildings would already be enough
- Distance from "main" building with LTE (=link distance) is very small, 40-150m each but with pine trees blocking LoS in most cases
- All spectrum available on both 2.4 and 5GHz with ZERO congestion, next Wifi AP is 600 meters away and does not even show up on phones etc. Zero microwave ovens in 1km radius.

Current plan:
- Use 2.4GHz for backbone because of pine trees, 40MHz channel?
- Upgrade Teltonika LTE router (horrible FW!) to SXT LTE6
- 1x omnidirectional AP in main building (Groove / Metal) on 2.4GHz on top of short tv antenna pole (~7m AGL)
- Feed SXT LTE6 with 48V PoE and omni AP off SXT LTE6 second PoE out port
- For 2 buildings with windows facing main building, WAP (ac) with 2.4GHz radio in client mode and 5GHz in AP
- For 2 buildings without windows toward main bld, SXTsq Lite2 (cheap) outside + another cheap AP inside

Do these products and setup make sense? Can I save money somewhere? Anything I should take into consideration when setting this up?

Thanks for any tips / experience!

If there is no line of sight, 2,4Ghz will never be stable. It will/can work - but it will be unstable. There is nothing you can do to fix this, but you can do it a bit "less worse" by not using omni in the middle, but using point to points to each cabin and then small APs to distribute in each cabin. (the WAP in a window is also not a good idea, try measuring link quality with and without window - glass window DO disturb signal.)
..:And btw, 40MHz is a No-go with no line of sight. The smaller the bandwidth the higher quality link you can expect. (I would've tried with 10MHz on PtP's).
Its much better with 10Mbit stable then 30Mbit with high packet loss.

But, as you can see I do not give you much hope to get a stable working network - for a stable working network you need to either use cables (preferably fiber) to each cabin, or cut trees to make proper Line of sight for Point to Point links.

u can see I do not give you much hope to get a stable working network - for a stable working network you need to either use cables (preferably fiber) to each cabin, or cut trees to make proper Line of sight for Point to Point links.

I appreciate your comments very much. Unfortunately running cables is very difficult as there are stretches of bare bedrock and even where we have soil (for the pines hehe) it is not deep at all. Mains electrical wiring is armored inside steel tubing when passing over these spots and there is no space in the tubes. We have issues with rabbits & squirrels eating through any exposed cabling.

I have now ordered a few directional antennas and will do tests with lower bandwidth channels.

Go with Mimo%# PTMP
PD: I don't want to get banned

Good luck :)
If cutting trees is not an option I would explore the option to get antennas OVER the trees.
Or find something licensed in lower bands than 2,4Ghz - there is 900MHz options out there.

Start with the LTE and see if you can even get a good speed from it.

We have provided service for some islands before. The main problem has been to get the internet there and to optimize the bandwidth, but you didn't mention that so I assume we are OK on that matter.

Since the area you have to cover is small I will consider 2 options:

1) A mesh: Changing to a mesh topology will increase your bandwidth and it will solve your trees problem
2) Fiber: If you are going to change the equipment anyway, is there a way to install a couple fiber cables to get to the main building? Then you can install PtP antennas to each building. This will reduce complexity and it will increase your bandwidth

So after doing some tests I did end up with
- Metal52ac using bundled antenna on main building running 2.4GHz
- SXTsq Lite 2 on each building
- SXT LTE6 for uplink

We get 50-80Mbps on the LTE on 2CA (800+1800MHz) which is fine.

Amazingly, the PtMP with Metal + SXTs works quite ok through all those pine trees. There was rate flapping and data loss on the links so now I'm allowing only MCS0 - MCS4 and they are very stable, giving 34Mbps per link on simple BTest, even in pouring rain.

So far so good.

Here is my worst link today with dry weather and sunshine.. and there are at least 4 pines in the way.