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Bluebottle
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Equivalent setup for SXT units

Sun Jul 22, 2012 12:34 am

My customer has remote exploration sites in the Arctic. We typically use Cisco equipment to create wireless bridges, but are looking for a more cost-effective solution.

We have tried the SXTG5HnD units and they worked quite well. However, we’re concerned about the environmental specifications – especially given that the unit is an all-in-one integrated device. Temperatures frequently drop below -60 in the winter at these sites, and we can’t have the equipment failing.

Normally we put the electronics portion of the bridge indoors, and have only the antenna outside. I was wondering about creating a similar setup using Mikrotik components.

I was thinking that the equivalent to the internal electronics of the SXT G unit would be the routerboard RB711G-5HnD – is that correct?

I just can’t work out the proper arrangement of antenna(s) and connectors to take full advantage of the performance offered by this hardware. It’s a dual chain setup, so does that mean 2 antennas? Or a special dual polarity antenna?

We’re typically looking at relatively short (a few hundred meters max) bridge distances. So what kind of antenna would be suitable to achieve the same kind of setups with the SXT G units?
 
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nickshore
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Re: Equivalent setup for SXT units

Mon Jul 23, 2012 4:16 pm

Use something like the Dual polarized panel antenna from IT Elite:
http://linitx.com/product/13348
 
n21roadie
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Re: Equivalent setup for SXT units

Mon Jul 23, 2012 6:11 pm

Use something like the Dual polarized panel antenna from IT Elite:
http://linitx.com/product/13348
That has on its spec
Min temperature: -40degC / -40degF which is incorrect
Max temperature: 80degC / 176degF

Maybe another suggestion is to have the SXT inside a plastic box which has its sides + top/bottom and rear insulated, you may lose a few db of signal but it should give you the operating temperature of -60C, could you test in a cold room at the lowest temperature it will go down to.
 
Bluebottle
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Re: Equivalent setup for SXT units

Mon Jul 23, 2012 8:15 pm

Thanks for the suggestions. I had thought about insulating or even putting a small DC powered ceramic heater in the box, powered off the POE. The trick is for cold installations - if the equipment will not start up from completely frozen, there needs to be a delay for the heater to do its work before applying power to the electronics. Insulation would do no good, either, if the unit is completely cold - as would happen in the event of an extended power outage.

I'm not AS concerned with the temp. rating of the antenna as with the electronics. An antenna can be swapped out by anyone on site with a ladder and a little instruction. Swapping out a routerboard would be much more involved and would most likely involve an unscheduled site visit by a tech (very expensive).

However, if anyone is aware of a better antenna, please speak up. Preferably one from a North American supplier :)

And -40F is the same as -40C, n21roadie :D
 
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BrinkNetworks
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Re: Equivalent setup for SXT units

Thu Aug 02, 2012 6:19 pm

There are several ways to go about the setup you're looking for - for a brief overview....

You only need one Dual Polarity Antenna per side.
The 7115HnD should work great.
You'll run LMR 400 or a similar cabling from the antenna to the radio.
Most of the antennas designed for this purpose come with either RP-SMA connectors or N-Male connectors
If you want to order pre-made cables - The most common end type will be N-Male or N-Fem .
Assuming you get an N-Male/N-Fem cable - you'll attach the N-Male to the antenna and then order a an N-Male to MMCX adapter to make the connection to the 7115HnD: http://www.balticnetworks.com/laird-n-m ... ail-8.html

To take it a step further - Most folks will buy an enclosure to house the radio - Something like this:

http://www.balticnetworks.com/mikrotik- ... proof.html

In the bottom of that enclosure - there are "BulkHead" connector knockouts for these cables:

http://www.balticnetworks.com/mikrotik- ... 36-cm.html

In that setup you'll have an N-Male to N-Male cable. If you don't want excess cabling and want to order the exact length premade - http://www.tessco.com can help you there.

Regarding the antennas - The larger you go the more gain. Given you're so close I can't imagine you'd need anything bigger than a 24db antenna - but that really depends on the length of the LMR you'll be running.

Hope that helps - don't hesitate to ask if you have any more questions!
 
Bluebottle
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Re: Equivalent setup for SXT units

Thu Aug 02, 2012 6:41 pm

Thanks, Brink! That's a lot of helpful info. With regards to cable, I'm an old hand at making cable for these purposes - including LMR. So I just order bulk and fabricate onsite to the exact specs needed.

The housing you show looks really good. ALthough in the environment this setup will be going in, the best housing in the world isn't going to help if the temperature of the electronics drops too low. I've been looking for some kind of heater setup that can preheat the box before turning on the electronics. Failing that, I'll just tend to situate the box indoors nearest the point where the antenna will go. Often this results in an antenna cable length of less than 3m. Given the shorter distances I'm working with, this should be fine.

A few questions maybe you can help with, though.

Am I over-engineering this with dual polarity antennas for what amounts to short hops? I'm assuming there's an increase in performance. Maybe I'm wrong, and the benefit of dual chain is more on the reliability side?

Also, if I wanted to do something similar to the Omnitik/SXT setup, how would I do a dual-polarity omnidirectional antenna? I'm thinking of a central radio as a hub to link up 3-5 remote radios to various buildings across the site. None of them would be more than 1-1.5 km away, and most 300-400 m.

Down the road, I may be looking at linking up two of the sites, which are about 40km apart. But one thing at a time!
 
Bluebottle
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Re: Equivalent setup for SXT units

Thu Aug 02, 2012 6:44 pm

re: my question about the omni dual polarity setup. I didn't realize they made dual polarity omnis - found them on the site you linked to (http://www.balticnetworks.com/ubiquiti- ... tenna.html). I couldn't find anything like that on other places I've checked.

Thanks again for the help!

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