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Short distance PtP suggestions

Hi everyone,

 

I am in need of connecting two buildings that are just over 4000 ft (1.2 km) from each other. The line of sight is NOT perfectly clear. There do not appear to be any major obstructions, i.e no tall building etc, just mostly some trees and a few roof peaks. The connection is not likely to need heavy bandwidth. Mostly to tie into active directory login and general file sharing. No video or minimal video on occasion.

 

My thoughts are that I should use one of the units capaple of 900 mhz to cut through the clutter. I'd like to try avoid having to put up raised antenna mast if possible. Both buildings are already 2 1/2 story in height. The RocketM and NanoStationM both appear to be possibilities, but I have never used either up to date. Am I headed in the right direction? Can anyone suggest for or against a specific setup?

 

I've looked at a few other similar posts in the forum, but most seem to have extremely short distances- so I can't exactly find a comparable situation at the moment.

 

Thank you in advance!

Senior Member
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Re: Short distance PtP suggestions

Any chance you have a picture of the path? That would help.

 

900 may work, but you will have minimal speed. 

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Re: Short distance PtP suggestions

I'm going to try take a pic once the weather breaks. Thanks

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Re: Short distance PtP suggestions

For the price I'd give a pair of powerbeam m2 400's a try.

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Re: Short distance PtP suggestions

[ Edited ]

first ot all, 4000 ft  is not exactly a "short distance", I just installed 100ft PtP link Man Happy

 

my rule: no clear line of sight, no link

 

trees are the worst, even if they look like the least problem - they move from the wind and they contains water

 

finally - lower frequencies penetrate obstacles better, but lower frequencies also have bigger Fresnel zone, actually I don't know which one is more important

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Re: Short distance PtP suggestions

Thanks for the thoughts so far. Short distance is obviously relative. I understand your statements, but if I was talking about 100 ft I would just use a regular access point. When I see the specs on some of the units being rated for 15 to 20 km, my 4000 ft is just over 1 km- hence my assessment as short distance.

 

So far it looks like I may be able to attain a direct line of sight if I elevate one end approximately 15 feet. While I was hoping to avoid raising a pole mount on either end- I think a 15 to 20 ft rise to achieve direct LOS is better value than attempting to power through a few obstructions. I'm hoping to have some exact measurements tomorrow.

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Re: Short distance PtP suggestions

Yep, LOS always wins. Free-space path loss attenuation is a fraction of the attenuation of a tree or building.  Use a smaller gain (or grid style) antenna at your elevated end to reduce wind load and make up the gain with a larger antenna at the other end.

 

 

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Re: Short distance PtP suggestions

[ Edited ]

@dszumwrote:

When I see the specs on some of the units being rated for 15 to 20 km


Even ubiquiti employees on this forum often write this is not real life achieved distance. Why? Because that distance in specs means you can create link on that distance (maybe), but it will be lowest possible speed on the world, but yes - link will be established. To achieve usable tens or hundrets megabites speed, distance need to be much lower.

 

If you want to choose correct radio/antenna models, this is best for you, as it can calculate real speed with your distance and radio/antenna model link.ubnt.com or the old version airlink.ubnt.com

 

I like the old version, because you can select different radio models and then see achievable speed.

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Re: Short distance PtP suggestions

to say airlink is optimistic is a huge understatement

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Re: Short distance PtP suggestions

There are things airLink doesn't know about your link, so I refer to it as a prediction for that reason rather than a guarantee.
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Re: Short distance PtP suggestions

[ Edited ]

@scrachawrote:

to say airlink is optimistic is a huge understatement


simply because that maps knows only terrain, not buildings, trees etc

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Re: Short distance PtP suggestions

I finally made it to the roof this weekend, and sadly I can say- even with a 20 foot rise over roofline- I cannot clear enough trees.

 

I do have a smokestack on a neighborhood school in clear view from both facilities, but no clear line to each building so far.

 

Unless the school may be willing to let me mount two antenna or dished on that stack, I may be stuck using a wired VPN, which will limit me drastically.

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Re: Short distance PtP suggestions

That is unfortunate. How many of them can you clear? Is it partially clear or totally blocked?
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Re: Short distance PtP suggestions

If it's only one or two trees I'd still give it a go with a pair of 2.4GHz radios.  

 

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Re: Short distance PtP suggestions

I definitely would not. Trees are moved by wind, they containt water, depending where you are they can be covered by snow (what is more water). At least ask the school so you know your options.

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Re: Short distance PtP suggestions

I've probably got at least 3 to 4 good sized trees in the way. Winter they are bare except for possible snow load. Summer they will be pretty full. I'm going to see if the local school can work with me or not. I have a local private tower nearby as well that may be an option, but I'm trying to avoid any major or recurring costs.

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Re: Short distance PtP suggestions

My concern about setting this up to shoot through four trees, although we don't know the type or size of these trees, would be your recurring costs growing throughout the year as the foliage returns and various weather conditions impact your performance.
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Re: Short distance PtP suggestions

hi,

 

if you think outside the box then the smoke stack maybe your saviour.

 

If you used 5GHz narrow beam kit like the 400 or larger dishes then point each end at the smoke stack.

 

If it is a reasonable diameter you should be able to get enough reflected signal to make a working link.

 

If you have a bulding both ends can see that is in the same plane (so both aerials would point the same way to it) then even better. If it is metal clad even better still Man Happy

 

It will all be down to angles and EiRP limits etc..

 

This works better with flat walls but we have customers bouncing signals off a wall to get around trees on a similar length path and it works fine.

 

Bill Lewis
Kijoma Broadband
UK 5 GHz WISP - ISPA UK, RIPE Member
Senior Design Eng , RF / Network Eng.
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