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Possible to bounce 5.8ghz Rf off (tree, building) because no LOS.
Posted by
Dehv
on 30 Mar, 2022 03:02
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Trying to build a long distance wifi bridge 10km away with no line of sight.
There is a very high tree nearby that would likely have line of sight; 200 m from base.
1) assuming no wind sway, is it possible to install a surface/ grid - to bounce a high gain dish antenna off of, or
2) what about 2 yagis passively coupled, one aimed at long target, one at near target. Would there be too many cable losses to be purely passive, or would I have to run a solar panel powered repeater type thing?
Thoughts appreciated.
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#1 Reply
Posted by
richard.cs
on 30 Mar, 2022 10:04
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I suspect a pair of yagis would be easier to aim than grid reflector, and the gain should also be beneficial. I would expect it to work OK passively, but it is easily calculable as you just do the path loss equation for both hops, sum them, and add in your cable loss. If you're mounting the yagis in the tree don't go overboard on the gain or the wind sway will cause problems.
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#2 Reply
Posted by
tggzzz
on 30 Mar, 2022 10:09
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The regulations are written so that if you increase the directionality of the transmit antenna by, say, 20dB, then you must reduce the transmit power by 20dB. That is to prevent you screwing up other users of the band.
You can increase the directionalty of a receive antenna.
You should take into account the effect of the fresnel zone
https://en.wikipedia.org/wiki/Fresnel_zoneFor your usage, is it wise to ignore the effects of wind sway?
How much sway would be too much?
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#3 Reply
Posted by
richard.cs
on 30 Mar, 2022 10:24
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The regulations are written so that if you increase the directionality of the transmit antenna by, say, 20dB, then you must reduce the transmit power by 20dB. That is to prevent you screwing up other users of the band.
In this case however I see no regulatory problem with high gain antennas on both sides of a
passive repeater because:
- It won't meet the definition of a transmitter, it's just some bits of metal hanging in the breeze.
- The ERP of (whichever side is currently) the transmitting side, being limited by the received power the other side, will be microscopic.
High gain antennas at the endpoints may be more problematic, but I am not familiar with Canadian rules. Assuming similar to here, for a bidirectional link you put high gain antennas both ends, but also wind down the TX power both ends by the gain of one antenna as tggzzz says, you therefore gain half as much as you might as hoped, i.e. 20 dB each end only gains you 20 dB total not 40 dB.
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#4 Reply
Posted by
Gyro
on 30 Mar, 2022 10:42
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Deciduous or evergreen? Presumably you'd be mounting to the trunk rather than an outlying branch, you might need to account for a seasonally variable attenuator.
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#5 Reply
Posted by
Marco
on 30 Mar, 2022 10:54
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The regulations are written so that if you increase the directionality of the transmit antenna by, say, 20dB, then you must reduce the transmit power by 20dB. That is to prevent you screwing up other users of the band.
That's EU. US allows increased EIRP for higher gain antennas, dunno about Canada.
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#6 Reply
Posted by
Dehv
on 30 Mar, 2022 11:23
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Very interesting info, thanks to all. With signal limited to whatever default power is - half or quarter watt? I had no idea the gain would need to be reduced.
Regarding fresnel zone, with such a small wavelength of 5.8ghz in open air I wonder how that would even be an issue with medium to high directional ant? Other than potential destructive phase reflections with low gain ant.
I recall vaguely there were a couple 5.8 bands that allowed higher power (4?) Watt, rather than the usual quarter or half W norm.
Maybe that would be worth a tree climb for the passive yagis,
With a 3ft sat dish parabola from the long shot (9km), and nanostation type medium gain grid array at the near side.
The tree is an over 100 year old spruce that my grandfather limbed up to the crown, about 4 foot diameter at the base. No limbs up to maybe 50 or 60ft.
Thanks again for all the advice so far!
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#7 Reply
Posted by
cdev
on 30 Mar, 2022 12:06
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Yes, there would be a quite substantial loss involved, ( 60-80-90 db? or more ) but not so much that it would not work, probably. Especially if you could place a active repeater at that location. (with power)
Perhaps you could try a dual periscope design with two 45 degree reflectors so you could place an access point with two high gain antennas at the base for easier maintenance.
wind loading and tree growth might be substantial problems over time. Its a bit like EME..
I dont have any experience doing this.
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#8 Reply
Posted by
tggzzz
on 30 Mar, 2022 14:22
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Regarding fresnel zone, with such a small wavelength of 5.8ghz in open air I wonder how that would even be an issue with medium to high directional ant? Other than potential destructive phase reflections with low gain ant.
I believe I saw that across an open field, but as I wasn't doing the installation I didn't investigate it.
Given how much propagation varies from minute to minute and season to season, I suspect the other problems are more significant. But if you fix those, fresnel might cause problems.
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#9 Reply
Posted by
Dehv
on 30 Mar, 2022 19:26
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Dual periscope... hmm interesting. Maybe with such a short cable length internally losses could be minimized. For active, really dont want to be climbing the tree every time it needs a power cycle though... hahaha
Regarding wind, I'd be happy if it worked half the time, for bulk downloads. There is not much wind around here, in a patch of boreal forest.
Which problems other than fresnel?
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#10 Reply
Posted by
Dehv
on 30 Mar, 2022 19:28
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Which other problems come to mind?
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#11 Reply
Posted by
Ian.M
on 30 Mar, 2022 20:39
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Critters!
Make sure your repeater antennae don't have any open cavities the critters can stuff full of (pine) nuts, nest in or otherwise trash. Also unprotected cables can get chewed!
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#12 Reply
Posted by
Dehv
on 30 Mar, 2022 21:38
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And wasps! And bears!
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#13 Reply
Posted by
tggzzz
on 30 Mar, 2022 21:49
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Which problems other than fresnel?
The standard RF propagation issues, as mentioned by others in this thread.
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#14 Reply
Posted by
m3vuv
on 31 Mar, 2022 10:44
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Dont know if it helps but once used an old sky dish to receive 2.4 ghx wifi,just cut down a 2.4ghz yaggi and nounted the dipole part in place of the lnb,it worked well,that was running 1 watt.
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#15 Reply
Posted by
cdev
on 01 Apr, 2022 23:00
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Reminds me of a buch of web pages in the early days of wifi describing the conversion of old offset feed satellite dishes for wifi, it was a quite popular mod for the dish network style dishes. They end up with around 24 db gain and people have used them to make 20 mile plus wifi links. Google "Trevor Marshall"
Note, these web pages are all very old.. The key part of the mod is the feed assembly/creation of a dipole with balun.. which is the difficult part to get right.
The best performance actually I think uses a biquad at the focus of the shallow offset feed (not prime focus) dish. Biquad feed is a quick 2.4 GHz antenna to make and 6-8 db gain, bidirectional.. In San Francisco one in the window of my old apartment was able to let me go as far as two cafes located in the middle of the next block, maybe 500-600 meters away, with a strong two way wifi signal. This was as good as a commercial 12 element yagi that I had and still have, my best commercial wifi antenna. The pattern is pretty wide too. enough to make this basic biquad with C shaped metal reflector a very useful easy to build antenna.
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#16 Reply
Posted by
El Rubio
on 05 Apr, 2022 00:40
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Just curious, but what kind of performance are you hoping to get? I don’t have long range wifi experience, but have worked with microwave and wireless data. A couple of things come to mind. Is there just the one tree in all of the 10km path? How high are you mounting your antennas? Anything blocking or partially blocking true line of sight will affect it. The passive repeater will not likely make the 9.8km hop. Then there is latency. Assuming everything is working perfectly, there is a lag because of the path distance that will slow it down. I recall a 5-6GHz single hop over a swamp (6 miles). We used 2-3ft dish antennas on each end about 60 feet high on each end. Bottom line is you can overcome your obstacles, but it could end up being a major project. Good lick and post your progress. I’d love to see what you do and what works for you.
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#17 Reply
Posted by
LaserSteve
on 05 Apr, 2022 12:29
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