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Dragony
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Searching a 60 GHz passive repeater for 70° angle

Fri Jul 08, 2022 8:44 pm

Hello.

I want to connect two buildings with 60 GHz. Unfortunately there is no line of sight, so I have to go around a 70° corner. the total distance is around 800 meters. Also there is no power present on that point, so a passive solution would be great.

I have read about using two dishes and just connecting them with a cable might work. Is that true?

Another solution would be a low-energy active repeater, but I haven't found anything from Mikrotik. Does something like that exist?

The obvious solution, just to install two fully independent dishes with packet forwarding and connect them isn't favoured, because the power requirements with 20 Watts would need either big batteries or an additional solar installation.

Thanks for helping.
 
lambert
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Re: Searching a 60 GHz passive repeater for 70° angle

Sun Aug 21, 2022 12:33 pm

Perfectly flat sheet of (shiny?) metal mounted perpendicular to the bisection of the angle. Align both radios to center of the metal. Pretend you are shooting pool. I've not tried to set it up myself. I suspect it is complicated. You might use a laser pointer mounted where center of the radio's antenna will be from one end and adjust until the reflection hits the mount point of the receiver antenna's center. Then move the pointer to the other end.

There are several microwave reflectors on the mountains near me. The signal bounces off a series of the reflectors to get through the valleys to where it needs to go. The reflectors are about 7m by 5m.
 
r00t
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Re: Searching a 60 GHz passive repeater for 70° angle

Tue Aug 23, 2022 3:42 pm

Connecting two dishes is pretty much out of the question at these frequencies. That would be possible if it was 5GHz, but at 60GHz, the attenuation of any type of feed + cable + feed or even just waveguide is too much for this to work.

So flat metal piece is only way how to possibly do this on 60GHz. Some experimentation will be needed on how big this reflector needs to be.
There is plenty of information for passive repeaters for lower bands (see linked PDF "Passive Repeater Engineering, Microflect, Co. Inc, 1989" on https://en.wikipedia.org/wiki/Passive_repeater page for example for all the calculations) - but not much for 60GHz. Found this paper with some 60GHz results, but still only theoretical numbers: https://arxiv.org/pdf/1905.04794.pdf

If you are going to try it, make sure the reflector is perfectly smooth, like a mirror. Something like 2m x 2m size would be my guess on where to start and do some testing, first at shorter distances (maybe 100m around the corner of the building) to see if it's even doable or not.

Please let us know if you get any results, this is interesting topic...
 
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mkx
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Re: Searching a 60 GHz passive repeater for 70° angle

Tue Aug 23, 2022 10:44 pm

The most important part in radio link between two antennae is Fresnel Zone. If it's (partially) obstructed at any point, signal gets attenuated more than free atmosphere attenuates it. Now, when talking about passive repeater (reflector), the idea is to have reflector covering most (if not all) of Fresnel Zone to reflect most (if not all) energy in new direction.

I've found an on-line Fresnel Zone calculator and according to it, the maximum width of Fresnel Zone of a 800 m long 60GHz link is slightly less than 1 meter. And that's at half of the link, it gets narrower at each end. So it should be fine to have reflector with width of about 1.22m and height of 1m (width should be wider than 1m because it's placed at angle of 70°/2 towards radio beam, hence beam becomes ellipse). And then the reflector should be exactly centered as @lambert described to cover all (or as much as possible) of Fresnel Zone.

In theory you could use a fine mesh instead of solid metal plate. However the granularity of the mesh should be less than wavelength, at 60GHz that's 5 mm and to make sure best performance I'd go with finer mesh (e.g. 2 mm). So it's probalby easier to go with solid plate with solid support.
 
sinisa
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Re: Searching a 60 GHz passive repeater for 70° angle

Thu Mar 14, 2024 5:08 pm

Old thread, but someday someone might find it useful:
I had two buildings connected with 60Ghz Wireless Wire Dishes. Distance about 650m. Everything working perfectly, even in rain and snow.
At some moment, a high building "appeared" in the middle of that path. First signal started fading, then disappeared completely. Only when I got to the roof I saw the new building.
While on roof, I looked around and saw a flat wall, without windows or anything, of a mall, so I directed both WWDs at approximately same angle to that wall (I was lucky it is close to the LoS, so both locations see it at an angle of about 45 degrees). Checked with Google Maps to find the best spot to aim antennae to, and now I have my 1Gbps link up again. Distance is now reported as 750m. Link goes down in very heavy rain, but that never lasts more than a few minutes here and doesn't happen more that once or twice in a year.
"Repeater" as passive as it can be :)
 
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Re: Searching a 60 GHz passive repeater for 70° angle

Thu Mar 14, 2024 5:13 pm

"Repeater" as passive as it can be :)
Improvise, adapt, overcome. :lol:
 
lambert
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Re: Searching a 60 GHz passive repeater for 70° angle

Thu Mar 14, 2024 6:23 pm

I'm curious what the material and finish of the Mall wall is. Is it metal or stone/stucco? Is it smooth or textured? It's great that you found a working solution.

I wonder if you could play with the channel for the link to find a couple of extra percentage in the link quality and reduce your rain fade. You've probably already thought of and done that.
 
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sirbryan
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Re: Searching a 60 GHz passive repeater for 70° angle

Thu Mar 14, 2024 6:57 pm

I ran into this when trying to install a customer's connection. It was at 5GHz, not 60GHz, but concept was the same. I was trying to align it down my side of the street, straight towards the AP, but it was going through a couple of trees. I was watching my phone while turning the radio and noticed that it was getting better way off-axis. After a couple of sweeps back and forth, I left it there, looked up, and realized I was bouncing it off the façade of a building across the street, approximately halfway down. It was much more stable than trying to go through the trees, so I left it.
 
sinisa
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Re: Searching a 60 GHz passive repeater for 70° angle

Fri Mar 15, 2024 11:28 am

I'm curious what the material and finish of the Mall wall is. Is it metal or stone/stucco? Is it smooth or textured? It's great that you found a working solution.
I am not sure, but I think it is some "fast building" material, with insulation and couple layers of paint over it. Smooth as a wall :)
I wonder if you could play with the channel for the link to find a couple of extra percentage in the link quality and reduce your rain fade. You've probably already thought of and done that.
Actually did that, SNR is a bit better with higher frequencies.

5GHz "backup" connection with a pair of DiscLite5ac also works, but with many link downs (signal -80/-82dBm, SNR 24dB) and the speed is not great, but enough to get me connectivity in case the main link should fail, to be able to check the equipment on the other side.

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